Ornithine decarboxylase (ODC) is a rate-limiting enzyme in the biosynthesis of polyamines (putrescine, spermidine, spermine), which orchestrate essential physiological and pathologic processes including embryogenesis, organogenesis, and neoplastic cell growth (Bello-Fernandez et al., 1993; Pendeville et al., 2001). We recently described a new autosomal dominant genetic disorder (Bachmann-Bupp syndrome, OMIM #619075) caused by a heterozygous de novo variant in the ODC1 gene in a 3-year-old girl with phenotypic features that included alopecia universalis and global developmental delay (Figure 1; Bupp et al., 2018). The nonsense variant caused premature abrogation of 14-aa residues in the C-terminus of the protein (ODC, p·K448X, Figure 2), leading to enhanced function. Red blood cells from the patient exhibited elevated ODC activity and putrescine levels compared to healthy controls. Four additional patients with similar mutations and phenotypic features of this syndrome have since been reported (Rodan et al., 2018) and at least four more cases have been identified.

Figure 1

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Figure 2

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Remarkably, these patients all represent human phenotypes of a transgenic mouse described in 1996, overexpressing C-terminally deleted ODC in the dermal tissue, leading to higher ODC enzyme activity and increased putrescine biosynthesis (Soler et al., 1996). The phenotypic changes first described in a mouse model included hair loss that was reversible with ODC inhibitor α-difluoromethylornithine (DFMO; common name eflornithine) (Soler et al., 1996). Experiments with the patient’s cultured primary dermal fibroblasts showed eflornithine reduced ODC activity, resulting in putrescine levels comparable to controls without affecting cell morphology or inducing cell death (Schultz et al., 2019).

Based on previously published murine data with eflornithine for gain-of-function variants (Soler et al., 1996), multiple long-term safety studies for clinical use in African sleeping sickness (trypanosomiasis), colorectal cancer, and neuroblastoma (Alirol et al., 2013; Priotto et al., 2009; Saulnier Sholler et al., 2015; Meyskens et al., 2008), and the absense of toxicity in the patient’s primary cell culture inresponse to eflornithine (Schultz et al., 2019), we surmised eflornithine might be a novel therapy for patients with this syndrome.

The novel treatment of this ultra-rare (less than 10 known cases) genetic syndrome presented unique challenges for monitoring efficacy over time. Growth parameters and metabolite levels were monitored easily, whereas others such as cognitive and motor functioning proved challenging, making us dependent on her standardized neurological examination.

Eflornithine improves clinical findings

The patient was born with a full head of silver-blond hair similar to a previously described murine phenotype (Soler et al., 1996), which fell out in early months and she remained hairless other than a few scattered, long hairs on the scalp. One month into treatment, hair growth was noted, with eyebrows appearing first (Figure 1B–C). Two months into treatment, scalp hair began to diffusely appear in the normal pattern of hair distribution increasing to resemble normal growth for age (Figure 1). She had a history of recurring follicular cyst formation and enlargement. Multiple lesions located on the posterior scalp and back that first were small maculopapular pustules slowly increased in size to approximately 6–7 cm in diameter (Figure 1B). These lysed spontaneously, but some would enlarge until painful, requiring surgical removal. Upon initiation of eflornithine, the formation of cysts ceased immediately (Figure 1B).

Prior to therapy, she had delayed development which manifested with no standing, cruising, or sitting, and limited fine motor skills. Her BMI increased during eflornithine treatment from 25th percentile to 90th percentile primarily due to increase in weight. This quantitative change was not accompanied by any change in body habitus but rather an increase in muscle bulk. She gained muscle strength demonstrated by acquisition of her ability to hold up her head without support (Figure 1B). As the video file shows after 4 months of eflornithine therapy, she was able to sit unsupported and maintain posture with the physical therapist providing resistance, use a walker, and feed herself with a spoon with some assistance. Video 1 allows for optimal visualization of this rapid improvement of our patient with this gain-of-function mutation in the ODC1 gene. The drastic external change in hair growth, and visible improvement in coordination, attention, and interaction can be clearly seen.

Video 1

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A neonatal brain MRI showed abnormal cerebral white matter and subependymal cysts (Figure 1D). Repeat MRI done at the end of the 9-month treatment trial with eflornithine demonstrated normalization of the cerebral white matter signal with decrease in volume with white matter loss and resolution of all previously noted cysts. Post-treatment magnetic resonance spectroscopy was also performed showing normalization of the N-acetylaspartate and choline signals relative to creatine Figure 1D.

The introduction of both whole genome and exome sequencing into clinical practice has led to rare diseases being diagnosed at rates never before seen (Turro et al., 2020; Tarailo-Graovac et al., 2016; Splinter et al., 2018). There are over 6000 rare diseases (incidence of greater than 1 in 2000 people) with over 300 million people worldwide affected (Nguengang Wakap et al., 2020). Though collectively common, each rare disease is unique making it challenging to develop specific therapies.

The process of developing treatment options for these rare diseases starts with a description of the genetic abnormality and developing an understanding of the molecular disruptions downstream from the affected protein. Once the biochemical perturbations are identified, then the quest to identify a drug that will return molecular pathways to normal begins. In genetic diseases, the correct mechanism to adopt could be challenging as many options exist such as activating or repressing pathways, enzyme blockade therapy, gene therapy regimens (Mendell et al., 2017), and potentially circumventing or correcting a genetic mutation such as treatments for muscular dystrophy (Iyer et al., 2019). Taking a genetic defect to human trials requires cell cultures, animal studies, and phased trials to determine safety and efficacy of such therapies. For multiple patients, often with unique genetic variants, to see benefit from this process could take the best part of a decade even as identification of successful drugs has been enhanced by the Orphan Drug Act (Augustine et al., 2013; Griggs et al., 2009).

We show a more rapid strategy of matching a patient with an ultra-rare newly identified syndrome to a drug with subsequent treatment being able to safely correct many phenotypic features. Once the whole exome identified the biochemical pathway, we used data from a previously described transgenic mouse model and our published cell culture study to surmise, eflornithine therapy could be of benefit to the patient. Though experimental data suggested that eflornithine could be beneficial, there is a chasm between ex vivo and in vivo studies with difficulties in extrapolating efficacy or safety from a fibroblast study alone (Schultz et al., 2019). We were fortunate that studies existed for eflornithine in a large enough population to suggest dosage and safety (Alirol et al., 2013; Priotto et al., 2009; Saulnier Sholler et al., 2015; Meyskens et al., 2008).

Once therapy was initiated, some neurological improvement in the patient was noted with better posture, weight gain, reduction, elimination of cyst formation, and significant hair growth. Six months into therapy, she had fine motor capability that she previously lacked, such as the capacity to feed herself and sit with some support. Brain imaging also showed changes that are beyond what would be explained merely by the passage of time, suggesting improvement related to eflornithine treatment.

While COVID-19 restrictions interrupted neurological assessments over the treatment period, the improvements noted throughout the relatively short treatment period of 6 months are truly remarkable, especially given the neurological deterioration in the patient prior to eflornithine therapy. This could be especially consequential if we could initiate therapy in a neonate diagnosed early before neurological damage occurs. We are now aware of other patients identified that present with similar gain-of-function ODC variants and polyamine abnormalities such as elevated N-acetylputrescine (Rodan et al., 2018). The therapy outlined here should allow for replication of the findings with a promise for significant improvement in quality of life for these patients. For such patients we recommend continued monitoring of multiple metabolites including N-acetylputrescine and acisoga to ensure that eflornithine dosing and urea/polyamine metabolite levels stay within normal ranges. The advent of global metabolomics presents a unique opportunity not only to develop a complete understanding of the dyshomeostasis prior to therapy but also a way to appreciate the drug’s impact on interconnected metabolic cycles simultaneously and perhaps a means of identifying disruptions early and predicting adverse effects. This may lead to earlier initiation of therapy in future patients, thereby perhaps avoiding some of the neurological delay that has come to characterize the disease in our patient.

Data is provided in Source data 1.

1. 1. Alirol E
   2. Schrumpf D
   3. Amici Heradi J
   4. Riedel A
   5. de Patoul C
   6. Quere M
   7. Chappuis F

   (2013) Nifurtimox-Eflornithine Combination Therapy for Second-Stage Gambiense Human African Trypanosomiasis: Médecins Sans Frontières Experience in the Democratic Republic of the Congo

   Clinical Infectious Diseases 56:195–203.

   https://doi.org/10.1093/cid/cis886

   • Google Scholar
2. 1. Augustine EF
   2. Adams HR
   3. Mink JW

   (2013) Clinical trials in rare disease: challenges and opportunities

   Journal of Child Neurology 28:1142–1150.

   https://doi.org/10.1177/0883073813495959

   • PubMed
   • Google Scholar
3. 1. Bello-Fernandez C
   2. Packham G
   3. Cleveland JL

   (1993) The ornithine decarboxylase gene is a transcriptional target of c-Myc

   PNAS 90:7804–7808.

   https://doi.org/10.1073/pnas.90.16.7804

   • Google Scholar
4. 1. Bupp CP
   2. Schultz CR
   3. Uhl KL
   4. Rajasekaran S
   5. Bachmann AS

   (2018) Novel de novo pathogenic variant in the ODC1 gene in a girl with developmental delay, alopecia, and dysmorphic features

   American Journal of Medical Genetics Part A 176:2548–2553.

   https://doi.org/10.1002/ajmg.a.40523

   • Google Scholar
5. 1. Griggs RC
   2. Batshaw M
   3. Dunkle M
   4. Gopal-Srivastava R
   5. Kaye E
   6. Krischer J
   7. Nguyen T
   8. Paulus K
   9. Merkel PA

   (2009) Clinical research for rare disease: Opportunities, challenges, and solutions

   Molecular Genetics and Metabolism 96:20–26.

   https://doi.org/10.1016/j.ymgme.2008.10.003

   • Google Scholar
6. 1. Iyer S
   2. Suresh S
   3. Guo D
   4. Daman K
   5. Chen JCJ
   6. Liu P
   7. Zieger M
   8. Luk K
   9. Roscoe BP
   10. Mueller C
   11. King OD
   12. Emerson CP
   13. Wolfe SA

   (2019) Precise therapeutic gene correction by a simple nuclease-induced double-stranded break

   Nature 568:561–565.

   https://doi.org/10.1038/s41586-019-1076-8

   • Google Scholar
7. 1. Mendell JR
   2. Al-Zaidy S
   3. Shell R
   4. Arnold WD
   5. Rodino-Klapac LR
   6. Prior TW
   7. Lowes L
   8. Alfano L
   9. Berry K
   10. Church K
   11. Kissel JT
   12. Nagendran S
   13. L’Italien J
   14. Sproule DM
   15. Wells C
   16. Cardenas JA
   17. Heitzer MD
   18. Kaspar A
   19. Corcoran S
   20. Braun L
   21. Likhite S
   22. Miranda C
   23. Meyer K
   24. Foust KD
   25. Burghes AHM
   26. Kaspar BK

   (2017) Single-Dose Gene-Replacement Therapy for Spinal Muscular Atrophy

   New England Journal of Medicine 377:1713–1722.

   https://doi.org/10.1056/NEJMoa1706198

   • Google Scholar
8. 1. Meyskens FL
   2. McLaren CE
   3. Pelot D
   4. Fujikawa-Brooks S
   5. Carpenter PM
   6. Hawk E
   7. Kelloff G
   8. Lawson MJ
   9. Kidao J
   10. McCracken J
   11. Albers CG
   12. Ahnen DJ
   13. Turgeon DK
   14. Goldschmid S
   15. Lance P
   16. Hagedorn CH
   17. Gillen DL
   18. Gerner EW
   19. Jr, McLaren FL
   20. Pelot CE
   21. Hawk PM
   22. Lawson G

   (2008) Difluoromethylornithine plus sulindac for the prevention of sporadic colorectal adenomas: a randomized placebo-controlled, double-blind trial

   Cancer Prevention Research 1:32–38.

   https://doi.org/10.1158/1940-6207.CAPR-08-0042

   • Google Scholar
9. 1. Nguengang Wakap S
   2. Lambert DM
   3. Olry A
   4. Rodwell C
   5. Gueydan C
   6. Lanneau V
   7. Murphy D
   8. Le Cam Y
   9. Rath A

   (2020) Estimating cumulative point prevalence of rare diseases: analysis of the Orphanet database

   European Journal of Human Genetics 28:165–173.

   https://doi.org/10.1038/s41431-019-0508-0

   • Google Scholar
10. 1. Pendeville H
    2. Carpino N
    3. Marine JC
    4. Takahashi Y
    5. Muller M
    6. Martial JA
    7. Cleveland JL

    (2001) The ornithine decarboxylase gene is essential for cell survival during early murine development

    Molecular and Cellular Biology 21:6549–6558.

    https://doi.org/10.1128/MCB.21.19.6549-6558.2001

    • PubMed
    • Google Scholar
11. 1. Priotto G
    2. Kasparian S
    3. Mutombo W
    4. Ngouama D
    5. Ghorashian S
    6. Arnold U
    7. Ghabri S
    8. Baudin E
    9. Buard V
    10. Kazadi-Kyanza S
    11. Ilunga M
    12. Mutangala W
    13. Pohlig G
    14. Schmid C
    15. Karunakara U
    16. Torreele E
    17. Kande V

    (2009) Nifurtimox-eflornithine combination therapy for second-stage African Trypanosoma brucei gambiense trypanosomiasis: a multicentre, randomised, phase III, non-inferiority trial

    The Lancet 374:56–64.

    https://doi.org/10.1016/S0140-6736(09)61117-X

    • Google Scholar
12. 1. Rodan LH
    2. Anyane-Yeboa K
    3. Chong K
    4. Klein Wassink-Ruiter JS
    5. Wilson A
    6. Smith L
    7. Kothare SV
    8. Rajabi F
    9. Blaser S
    10. Ni M
    11. DeBerardinis RJ
    12. Poduri A
    13. Berry GT

    (2018) Gain-of-function variants in the ODC1 gene cause a syndromic neurodevelopmental disorder associated with macrocephaly, alopecia, dysmorphic features, and neuroimaging abnormalities

    American Journal of Medical Genetics Part A 176:2554–2560.

    https://doi.org/10.1002/ajmg.a.60677

    • Google Scholar
13. 1. Saulnier Sholler GL
    2. Gerner EW
    3. Bergendahl G
    4. MacArthur RB
    5. VanderWerff A
    6. Ashikaga T
    7. Bond JP
    8. Ferguson W
    9. Roberts W
    10. Wada RK
    11. Eslin D
    12. Kraveka JM
    13. Kaplan J
    14. Mitchell D
    15. Parikh NS
    16. Neville K
    17. Sender L
    18. Higgins T
    19. Kawakita M
    20. Hiramatsu K
    21. Moriya S-S
    22. Bachmann AS

    (2015) A phase I trial of DFMO targeting polyamine addiction in patients with relapsed/refractory neuroblastoma

    PLOS ONE 10:e0127246.

    https://doi.org/10.1371/journal.pone.0127246

    • Google Scholar
14. 1. Schultz CR
    2. Bupp CP
    3. Rajasekaran S
    4. Bachmann AS

    (2019) Biochemical features of primary cells from a pediatric patient with a gain-of-function ODC1 genetic mutation

    Biochemical Journal 476:2047–2057.

    https://doi.org/10.1042/BCJ20190294

    • Google Scholar
15. 1. Soler AP
    2. Gilliard G
    3. Megosh LC
    4. O'Brien TG

    (1996) Modulation of murine hair follicle function by alterations in ornithine decarboxylase activity

    Journal of Investigative Dermatology 106:1108–1113.

    https://doi.org/10.1111/1523-1747.ep12340155

    • Google Scholar
16. 1. Splinter K
    2. Adams DR
    3. Bacino CA
    4. Bellen HJ
    5. Bernstein JA
    6. Cheatle-Jarvela AM
    7. Eng CM
    8. Esteves C
    9. Gahl WA
    10. Hamid R
    11. Jacob HJ
    12. Kikani B
    13. Koeller DM
    14. Kohane IS
    15. Lee BH
    16. Loscalzo J
    17. Luo X
    18. McCray AT
    19. Metz TO
    20. Mulvihill JJ
    21. Nelson SF
    22. Palmer CGS
    23. Phillips JA
    24. Pick L
    25. Postlethwait JH
    26. Reuter C
    27. Shashi V
    28. Sweetser DA
    29. Tifft CJ
    30. Walley NM
    31. Wangler MF
    32. Westerfield M
    33. Wheeler MT
    34. Wise AL
    35. Worthey EA
    36. Yamamoto S
    37. Ashley EA

    (2018) Effect of genetic diagnosis on patients with previously undiagnosed disease

    New England Journal of Medicine 379:2131–2139.

    https://doi.org/10.1056/NEJMoa1714458

    • Google Scholar
17. 1. Squitti R
    2. Cerchiaro G
    3. Giovannoni I

    (2019) A case of a mild wolfram syndrome with concomitant ATP7B mutation

    CellR4 7:e2735.

    https://doi.org/10.32113/cellr4_20198_2735

    • Google Scholar
18. 1. Tarailo-Graovac M
    2. Shyr C
    3. Ross CJ
    4. Horvath GA
    5. Salvarinova R
    6. Ye XC
    7. Zhang L-H
    8. Bhavsar AP
    9. Lee JJY
    10. Drögemöller BI
    11. Abdelsayed M
    12. Alfadhel M
    13. Armstrong L
    14. Baumgartner MR
    15. Burda P
    16. Connolly MB
    17. Cameron J
    18. Demos M
    19. Dewan T
    20. Dionne J
    21. Evans AM
    22. Friedman JM
    23. Garber I
    24. Lewis S
    25. Ling J
    26. Mandal R
    27. Mattman A
    28. McKinnon M
    29. Michoulas A
    30. Metzger D
    31. Ogunbayo OA
    32. Rakic B
    33. Rozmus J
    34. Ruben P
    35. Sayson B
    36. Santra S
    37. Schultz KR
    38. Selby K
    39. Shekel P
    40. Sirrs S
    41. Skrypnyk C
    42. Superti-Furga A
    43. Turvey SE
    44. Van Allen MI
    45. Wishart D
    46. Wu J
    47. Wu J
    48. Zafeiriou D
    49. Kluijtmans L
    50. Wevers RA
    51. Eydoux P
    52. Lehman AM
    53. Vallance H
    54. Stockler-Ipsiroglu S
    55. Sinclair G
    56. Wasserman WW
    57. van Karnebeek CD

    (2016) Exome sequencing and the management of neurometabolic disorders

    New England Journal of Medicine 374:2246–2255.

    https://doi.org/10.1056/NEJMoa1515792

    • Google Scholar
19. 1. Turro E
    2. Astle WJ
    3. Megy K
    4. Gräf S
    5. Greene D
    6. Shamardina O
    7. Allen HL
    8. Sanchis-Juan A
    9. Frontini M
    10. Thys C
    11. Stephens J
    12. Mapeta R
    13. Burren OS
    14. Downes K
    15. Haimel M
    16. Tuna S
    17. Deevi SVV
    18. Aitman TJ
    19. Bennett DL
    20. Calleja P
    21. Carss K
    22. Caulfield MJ
    23. Chinnery PF
    24. Dixon PH
    25. Gale DP
    26. James R
    27. Koziell A
    28. Laffan MA
    29. Levine AP
    30. Maher ER
    31. Markus HS
    32. Morales J
    33. Morrell NW
    34. Mumford AD
    35. Ormondroyd E
    36. Rankin S
    37. Rendon A
    38. Richardson S
    39. Roberts I
    40. Roy NBA
    41. Saleem MA
    42. Smith KGC
    43. Stark H
    44. Tan RYY
    45. Themistocleous AC
    46. Thrasher AJ
    47. Watkins H
    48. Webster AR
    49. Wilkins MR
    50. Williamson C
    51. Whitworth J
    52. Humphray S
    53. Bentley DR
    54. Abbs S
    55. Abulhoul L
    56. Adlard J
    57. Ahmed M
    58. Aitman TJ
    59. Alachkar H
    60. Allsup DJ
    61. Almeida-King J
    62. Ancliff P
    63. Antrobus R
    64. Armstrong R
    65. Arno G
    66. Ashford S
    67. Astle WJ
    68. Attwood A
    69. Aurora P
    70. Babbs C
    71. Bacchelli C
    72. Bakchoul T
    73. Banka S
    74. Bariana T
    75. Barwell J
    76. Batista J
    77. Baxendale HE
    78. Beales PL
    79. Bennett DL
    80. Bentley DR
    81. Bierzynska A
    82. Biss T
    83. Bitner-Glindzicz MAK
    84. Black GC
    85. Bleda M
    86. Blesneac I
    87. Bockenhauer D
    88. Bogaard H
    89. Bourne CJ
    90. Boyce S
    91. Bradley JR
    92. Bragin E
    93. Breen G
    94. Brennan P
    95. Brewer C
    96. Brown M
    97. Browning AC
    98. Browning MJ
    99. Buchan RJ
    100. Buckland MS
    101. Bueser T
    102. Diz CB
    103. Burn J
    104. Burns SO
    105. Burren OS
    106. Burrows N
    107. Calleja P
    108. Campbell C
    109. Carr-White G
    110. Carss K
    111. Casey R
    112. Caulfield MJ
    113. Chambers J
    114. Chambers J
    115. Chan MMY
    116. Cheah C
    117. Cheng F
    118. Chinnery PF
    119. Chitre M
    120. Christian MT
    121. Church C
    122. Clayton-Smith J
    123. Cleary M
    124. Brod NC
    125. Coghlan G
    126. Colby E
    127. Cole TRP
    128. Collins J
    129. Collins PW
    130. Colombo C
    131. Compton CJ
    132. Condliffe R
    133. Cook S
    134. Cook HT
    135. Cooper N
    136. Corris PA
    137. Furnell A
    138. Cunningham F
    139. Curry NS
    140. Cutler AJ
    141. Daniels MJ
    142. Dattani M
    143. Daugherty LC
    144. Davis J
    145. De Soyza A
    146. Deevi SVV
    147. Dent T
    148. Deshpande C
    149. Dewhurst EF
    150. Dixon PH
    151. Douzgou S
    152. Downes K
    153. Drazyk AM
    154. Drewe E
    155. Duarte D
    156. Dutt T
    157. Edgar JDM
    158. Edwards K
    159. Egner W
    160. Ekani MN
    161. Elliott P
    162. Erber WN
    163. Erwood M
    164. Estiu MC
    165. Evans DG
    166. Evans G
    167. Everington T
    168. Eyries M
    169. Fassihi H
    170. Favier R
    171. Findhammer J
    172. Fletcher D
    173. Flinter FA
    174. Floto RA
    175. Fowler T
    176. Fox J
    177. Frary AJ
    178. French CE
    179. Freson K
    180. Frontini M
    181. Gale DP
    182. Gall H
    183. Ganesan V
    184. Gattens M
    185. Geoghegan C
    186. Gerighty TSA
    187. Gharavi AG
    188. Ghio S
    189. Ghofrani H-A
    190. Gibbs JSR
    191. Gibson K
    192. Gilmour KC
    193. Girerd B
    194. Gleadall NS
    195. Goddard S
    196. Goldstein DB
    197. Gomez K
    198. Gordins P
    199. Gosal D
    200. Gräf S
    201. Graham J
    202. Grassi L
    203. Greene D
    204. Greenhalgh L
    205. Greinacher A
    206. Gresele P
    207. Griffiths P
    208. Grigoriadou S
    209. Grocock RJ
    210. Grozeva D
    211. Gurnell M
    212. Hackett S
    213. Hadinnapola C
    214. Hague WM
    215. Hague R
    216. Haimel M
    217. Hall M
    218. Hanson HL
    219. Haque E
    220. Harkness K
    221. Harper AR
    222. Harris CL
    223. Hart D
    224. Hassan A
    225. Hayman G
    226. Henderson A
    227. Herwadkar A
    228. Hoffman J
    229. Holden S
    230. Horvath R
    231. Houlden H
    232. Houweling AC
    233. Howard LS
    234. Hu F
    235. Hudson G
    236. Hughes J
    237. Huissoon AP
    238. Humbert M
    239. Humphray S
    240. Hunter S
    241. Hurles M
    242. Irving M
    243. Izatt L
    244. James R
    245. Johnson SA
    246. Jolles S
    247. Jolley J
    248. Josifova D
    249. Jurkute N
    250. Karten T
    251. Karten J
    252. Kasanicki MA
    253. Kazkaz H
    254. Kazmi R
    255. Kelleher P
    256. Kelly AM
    257. Kelsall W
    258. Kempster C
    259. Kiely DG
    260. Kingston N
    261. Klima R
    262. Koelling N
    263. Kostadima M
    264. Kovacs G
    265. Koziell A
    266. Kreuzhuber R
    267. Kuijpers TW
    268. Kumar A
    269. Kumararatne D
    270. Kurian MA
    271. Laffan MA
    272. Lalloo F
    273. Lambert M
    274. Allen HL
    275. Lawrie A
    276. Layton DM
    277. Lench N
    278. Lentaigne C
    279. Lester T
    280. Levine AP
    281. Linger R
    282. Longhurst H
    283. Lorenzo LE
    284. Louka E
    285. Lyons PA
    286. Machado RD
    287. MacKenzie Ross RV
    288. Madan B
    289. Maher ER
    290. Maimaris J
    291. Malka S
    292. Mangles S
    293. Mapeta R
    294. Marchbank KJ
    295. Marks S
    296. Markus HS
    297. Marschall H-U
    298. Marshall A
    299. Martin J
    300. Mathias M
    301. Matthews E
    302. Maxwell H
    303. McAlinden P
    304. McCarthy MI
    305. McKinney H
    306. McMahon A
    307. Meacham S
    308. Mead AJ
    309. Castello IM
    310. Megy K
    311. Mehta SG
    312. Michaelides M
    313. Millar C
    314. Mohammed SN
    315. Moledina S
    316. Montani D
    317. Moore AT
    318. Morales J
    319. Morrell NW
    320. Mozere M
    321. Muir KW
    322. Mumford AD
    323. Nemeth AH
    324. Newman WG
    325. Newnham M
    326. Noorani S
    327. Nurden P
    328. O’Sullivan J
    329. Obaji S
    330. Odhams C
    331. Okoli S
    332. Olschewski A
    333. Olschewski H
    334. Ong KR
    335. Oram SH
    336. Ormondroyd E
    337. Ouwehand WH
    338. Palles C
    339. Papadia S
    340. Park S-M
    341. Parry D
    342. Patel S
    343. Paterson J
    344. Peacock A
    345. Pearce SH
    346. Peden J
    347. Peerlinck K
    348. Penkett CJ
    349. Pepke-Zaba J
    350. Petersen R
    351. Pilkington C
    352. Poole KES
    353. Prathalingam R
    354. Psaila B
    355. Pyle A
    356. Quinton R
    357. Rahman S
    358. Rankin S
    359. Rao A
    360. Raymond FL
    361. Rayner-Matthews PJ
    362. Rees C
    363. Rendon A
    364. Renton T
    365. Rhodes CJ
    366. Rice ASC
    367. Richardson S
    368. Richter A
    369. Robert L
    370. Roberts I
    371. Rogers A
    372. Rose SJ
    373. Ross-Russell R
    374. Roughley C
    375. Roy NBA
    376. Ruddy DM
    377. Sadeghi-Alavijeh O
    378. Saleem MA
    379. Samani N
    380. Samarghitean C
    381. Sanchis-Juan A
    382. Sargur RB
    383. Sarkany RN
    384. Satchell S
    385. Savic S
    386. Sayer JA
    387. Sayer G
    388. Scelsi L
    389. Schaefer AM
    390. Schulman S
    391. Scott R
    392. Scully M
    393. Searle C
    394. Seeger W
    395. Sen A
    396. Sewell WAC
    397. Seyres D
    398. Shah N
    399. Shamardina O
    400. Shapiro SE
    401. Shaw AC
    402. Short PJ
    403. Sibson K
    404. Side L
    405. Simeoni I
    406. Simpson MA
    407. Sims MC
    408. Sivapalaratnam S
    409. Smedley D
    410. Smith KR
    411. Smith KGC
    412. Snape K
    413. Soranzo N
    414. Soubrier F
    415. Southgate L
    416. Spasic-Boskovic O
    417. Staines S
    418. Staples E
    419. Stark H
    420. Stephens J
    421. Steward C
    422. Stirrups KE
    423. Stuckey A
    424. Suntharalingam J
    425. Swietlik EM
    426. Syrris P
    427. Tait RC
    428. Talks K
    429. Tan RYY
    430. Tate K
    431. Taylor JM
    432. Taylor JC
    433. Thaventhiran JE
    434. Themistocleous AC
    435. Thomas E
    436. Thomas D
    437. Thomas MJ
    438. Thomas P
    439. Thomson K
    440. Thrasher AJ
    441. Threadgold G
    442. Thys C
    443. Tilly T
    444. Tischkowitz M
    445. Titterton C
    446. Todd JA
    447. Toh C-H
    448. Tolhuis B
    449. Tomlinson IP
    450. Toshner M
    451. Traylor M
    452. Treacy C
    453. Treadaway P
    454. Trembath R
    455. Tuna S
    456. Turek W
    457. Turro E
    458. Twiss P
    459. Vale T
    460. Geet CV
    461. Zuydam Nvan
    462. Vandekuilen M
    463. Vandersteen AM
    464. Vazquez-Lopez M
    465. von Ziegenweidt J
    466. Vonk Noordegraaf A
    467. Wagner A
    468. Waisfisz Q
    469. Walker SM
    470. Walker N
    471. Walter K
    472. Ware JS
    473. Watkins H
    474. Watt C
    475. Webster AR
    476. Wedderburn L
    477. Wei W
    478. Welch SB
    479. Wessels J
    480. Westbury SK
    481. Westwood J-P
    482. Wharton J
    483. Whitehorn D
    484. Whitworth J
    485. Wilkie AOM
    486. Wilkins MR
    487. Williamson C
    488. Wilson BT
    489. Wong EKS
    490. Wood N
    491. Wood Y
    492. Woods CG
    493. Woodward ER
    494. Wort SJ
    495. Worth A
    496. Wright M
    497. Yates K
    498. Yong PFK
    499. Young T
    500. Yu P
    501. Yu-Wai-Man P
    502. Zlamalova E
    503. Kingston N
    504. Walker N
    505. Bradley JR
    506. Ashford S
    507. Penkett CJ
    508. Freson K
    509. Stirrups KE
    510. Raymond FL
    511. Ouwehand WH

    (2020) Whole-genome sequencing of patients with rare diseases in a national health system

    Nature 583:96–102.

    https://doi.org/10.1038/s41586-020-2434-2

    • Google Scholar

Acceptance summary:

The study elegantly demonstrates the use of an FDA-approved drug, Eflornithine, to treat, with considerable success, the neurological and skin manifestations of a child with a gain of function mutation of the ODC1 gene. The authors have addressed all of our concerns/comments and the manuscript in its revised form is now acceptable for publication at eLife.Decision letter after peer review:

Thank you for submitting your article "Repurposing Eflornithine to Treat a Patient with a Rare ODC1 Gain of Function Variant Disease" for consideration by eLife. Your article has been reviewed by 2 peer reviewers, and the evaluation has been overseen by a Reviewing Editor and Mone Zaidi as the Senior Editor. The reviewers have opted to remain anonymous.

The reviewers have discussed their reviews with one another, and the Reviewing Editor has drafted this to help you prepare a revised submission.

Essential revisions:

There was significant interest in the work overall as noted below from comments from both reviewers – the repurposing of FDA approved to treat existing diseases is of great interest to the scientific and medical community. There are however several issues that need to be addressed prior to the acceptance of this manuscript to eLife.

1) Where there side effects associated with administration of the drug and if so those be noted and described in detail with laboratory values/data provided when available

2) While the work is of interest a single case is presented, were additional patients treated and if so what was their outcome?

Reviewer #1:

In the present study, Rajasekaran et al. describe the clinical findings resulting from repurposing Eflornithine (ODC inhibitor), an FDA approved drug, for a metabolic rare disease caused by pathogenic gain-of-function variants in ODC1. Based on their previous case report (PMID: 30239107), the authors observed that the clinical findings of their patient (alopecia, brain and scalp cystic lesions, and a variety of metabolites) improved after Eflornithine treatment. The study provides intriguing new insights into the treatment of this ultra-rare condition, and highlights the success of repurposing drugs for metabolic disease, but is limited by the single patient treated and lack of information about side effects.

1. Eflornithine is an inhibitor of ODC. Were there any side effects observed in the patient during the treatment process, especially during the period of dosage adjustment?

2. Myelosuppression is common in patients taking Eflornithine. Were complete blood cell counts measured before, during, and after the treatment? These should be included in the report.

3. Did the protein level of ODC change before and after treatment?

4. In the Discussion section, the authors mention the possibility of replication of findings in the current study in other patients with ODC1 gain-of-function. There is another report of 4 individuals with ODC1 gain-of-function variants (PMID: 30475435) which highlights the variable expressivity present among patients with this disorder. Replicating their findings in some of these other patients seems necessary before drawing conclusions about the efficacy of Eflornithine for effectively treating the clinical features of ODC1 gain-of-function variants. This is especially important since the authors were unable to perform neurological assessments for their study.

Reviewer #3:

This is an excellent paper which describes a rational and effective treatment for a very rare inherited condition.

The authors explain clearly the reasons for their using the drug selected based on the available literature with a transgenic mouse model and show very encouraging preliminary results that it will be effective.

There are a few corrections/additions which should be made to the manuscript.

1. The sentence starting on line 58 is ambiguous. Are there for additional patients with similar mutations that have been reported and four more cases or is the total number of cases actually known at present.

2. Some details of the low polyamine diet that was co-administered with the drug should be given and some discussion of whether this is likely to be a critical issue in the success of the treatment are needed. Since, as described in the paper, polyamine levels are intricately controlled by regulation of synthesis, degradation and uptake, it seems unlikely that uptake dietary polyamines would be a major issue in this condition which involves high levels that would be expected to suppress uptake.

3. Figure 2C would be very confusing to anyone not familiar with the ODC structure. It needs a longer explanation in either the text or the figure legend explaining that the protein is made up of two identical subunits which form to active sites at their interface. Showing the two subunits in different colors would be helpful. it is also confusing to show the two ends in different formulations without clearly explaining why this is done. The text would better if it referred to the two ODC monomers than two ODC proteins

A reference to the structure is needed eg for human (Almrud, J. J., Oliveira, M. A., Kern, A. D., Grishin, N. V., Phillips, M. A., and Hackert, M. L. (2000) Crystal structure of human ornithine decarboxylase at 2.1 Å resolution: structural insights to antizyme binding. J. Mol. Biol. 295, 7-16 ) or mouse (Kern, A. D., Oliveira, M. A., Coffino, P., and Hackert, M. L. (1999) Structure of mammalian ornithine decarboxylase at 1.6 Å resolution: stereochemical implications of PLP-dependent amino acid decarboxylases. Structure 7, 567-581).

4. A reference to the original work of the very gifted chemists and pharmacologists that lead to the conceptualization and production of DFMO would be appropriate. For example, Metcalf, B. W., Bey, P., Danzin, C., Jung, M. J., Casara, P., and Vevert, J. P. (1978) Catalytic irreversible inhibition of mammalian ornithine decarboxylase (E. C. 4. 1. 1. 17) by substrate and product analogues. J. Am. Chem. Soc. 100, 2551-2553.

Essential revisions:

There was significant interest in the work overall as noted below from comments from both reviewers – the repurposing of FDA approved to treat existing diseases is of great interest to the scientific and medical community. There are however several issues that need to be addressed prior to the acceptance of this manuscript to eLife.

1) Were there side effects associated with administration of the drug and if so those be noted and described in detail with laboratory values/data provided when available

Additional information about the safety screening procedure for this treatment is now included. No abnormalities were noted from any of the laboratory values monitored, and there were no clinically apparent side effects observed throughout this treatment. An updated paragraph detailing this information is now included both in methods section and the patient’s experience in the result section of the manuscript.

Methods section “These draws were performed in conjunction with safety screening that included at baseline, weekly after each dose increase and then twice monthly, which included a complete blood count, liver function test, lactate dehydrogenase, complete metabolic panel, calcium, magnesium, and phosphate. Audiograms were obtained pretreatment and then monthly. Electrocardiograms were done pretreatment, 1 month after first dose, and every 6 months, all based upon guidance from previous pediatric treatment trials with DFMO¹⁰”

In the Results section “All pre-treatment testing results were within normal limits, and through the duration of treatment, no abnormalities were noted in any of the described safety monitoring. This includes no gastrointestinal adverse effects or myelosuppression, previously noted in patients treated with DFMO.”

2) While the work is of interest a single case is presented, were additional patients treated and if so what was their outcome?

No, as with most rare diseases, we have a unique situation but there are new patients being identified with potential for benefit from DFMO treatment. These patients are in other locations receiving healthcare from other Institutions. The process of initiating DFMO needs careful planning and FDA involvement. We hope to continue to understand this condition with the potential for expanded treatment, one day. The publication of this report will go a long way to shed light on this rare disorder and highlight potential for therapy. To the best of our knowledge, there are currently no other patients with this disorder that have been treated with DFMO.

Reviewer #1:

In the present study, Rajasekaran et al. describe the clinical findings resulting from repurposing Eflornithine (ODC inhibitor), an FDA approved drug, for a metabolic rare disease caused by pathogenic gain-of-function variants in ODC1. Based on their previous case report (PMID: 30239107), the authors observed that the clinical findings of their patient (alopecia, brain and scalp cystic lesions, and a variety of metabolites) improved after Eflornithine treatment. The study provides intriguing new insights into the treatment of this ultra-rare condition, and highlights the success of repurposing drugs for metabolic disease, but is limited by the single patient treated and lack of information about side effects.

1. Eflornithine is an inhibitor of ODC. Were there any side effects observed in the patient during the treatment process, especially during the period of dosage adjustment?

We thank reviewer 1 for identifying this shortcoming as did the prior reviewer. Please see our response to as we did not identify any adverse effects to the patient during this treatment. Statements to that are now in both the methods and Results section.

2. Myelosuppression is common in patients taking Eflornithine. Were complete blood cell counts measured before, during, and after the treatment? These should be included in the report.

Complete blood counts were part of the safety monitoring during this treatment, and we did have access to other historical CBC results for this patient. There was no observed difference in counts during treatment, and a specific comment has been added to the manuscript noting this as it is an important matter to comment on.

3. Did the protein level of ODC change before and after treatment?

This is an excellent question and this is a limitation. We had previously measured the ODC levels of this patient in red blood cells and primary dermal skin fibroblasts before treatment and its response to DFMO. The previous publications showed both ODC proteins and enzymatic activity were significantly elevated compared to healthy controls and the levels dropped after DFMO. This is consistent with the hypothesis that the C-terminally deleted ODC leads to accumulated and active ODC protein in the patient (due to failure of the proteasome to clear the protein), resembling a gain-of-function (GOF) mutation. These observations were published prior to this study (Bupp et al., AMJG, 2018; Schultz et al., Biochem J, 2019). The use of western blot to measure protein levels has remained the traditional pathway to detect levels of intermediates before designing therapies for rare diseases. In this case we used the information from the previous study supported with global metabolomics done at different timepoints during therapy to determine that Putrescine was indeed elevated and dropped on therapy. After discussions with the FDA we pursued therapy through the more rapid compassionate use mechanism. Our hope is that this manuscript will highlight this approach as a model for using repurposed drug therapy rapidly with rapid advances in genetic diagnostics and need for rare disease treatments.

A statement is now added to the discussion as a limitation that says: “A limitation of this study is that we did not specifically measure enzymatic levels. In rare diseases, the enzyme activity and the resultant metabolic perturbation are traditionally studied in bench settings by detecting biochemical changes in the patient’s biological samples. This study used global metabolomics to measure polyamine levels serially as the patient underwent therapy.”.

4. In the Discussion section, the authors mention the possibility of replication of findings in the current study in other patients with ODC1 gain-of-function. There is another report of 4 individuals with ODC1 gain-of-function variants (PMID: 30475435) which highlights the variable expressivity present among patients with this disorder. Replicating their findings in some of these other patients seems necessary before drawing conclusions about the efficacy of Eflornithine for effectively treating the clinical features of ODC1 gain-of-function variants. This is especially important since the authors were unable to perform neurological assessments for their study.

Indeed, the phenotype may be variable, and the exact metabolic derangements need careful examination before therapy is initiated. We knew from the cell studies that she exhibited gain of function dyshomeostasis. In addition we utilized global metabolomics to map out the derangements at multiple timepoints. The presence of CAP/CLIA mandates allows the results to be reported in the Electronic Medical Record and allows treating physician to indeed initiate treatments. Our hope is that this initial manuscript highlights an approach that is more clinically practical in laying the groundwork for additional study and serves as a model for other ‘n of 1’ treatments.

One of the main limitations in rare disease research is the recruitment of patients from all over the world even if several have been identified, the challenge becomes how to get patients’ local hospital systems interested in novel trials particularly when these are often non-academic settings and how to balance the costs to families if recruitment is out of network or requires extensive travel. Thus, our hope is that this paper could open the possibility of navigating these challenges. In addition global metabolomics can be used to characterize the dyshomeostasis in each of these patients in the original healthcare institution.

A statement has now been added to the discussion that says “There are challenges in treating patients with rare diseases as the exact phenotype may be quite variable and the exact metabolic profile needs to be first established. Once therapy is indicated then the healthcare institution needs to be willing to navigate the regulatory hurdles to make the specific agent available for a single patient.”

Reviewer #3:

This is an excellent paper which describes a rational and effective treatment for a very rare inherited condition.

The authors explain clearly the reasons for their using the drug selected based on the available literature with a transgenic mouse model and show very encouraging preliminary results that it will be effective.

There are a few corrections/additions which should be made to the manuscript.

1. The sentence starting on line 58 is ambiguous. Are there for additional patients with similar mutations that have been reported and four more cases or is the total number of cases actually known at present.

We agree that this sentence is poorly worded and confusing to the reader. There are four additional patients with similar mutations that were reported by Rodan et al. in 2018 as well as four more cases that have been identified but not yet reported. We will edit the sentence in line 58 to clarify this statement.

It now reads “Four additional patients with similar mutations and phenotypic features of this syndrome have since been reported⁴ with at least four more cases identified in other centers, but not yet reported”.

2. Some details of the low polyamine diet that was co-administered with the drug should be given and some discussion of whether this is likely to be a critical issue in the success of the treatment are needed. Since, as described in the paper, polyamine levels are intricately controlled by regulation of synthesis, degradation and uptake, it seems unlikely that uptake dietary polyamines would be a major issue in this condition which involves high levels that would be expected to suppress uptake.

The consideration of polyamines in diet, its impact with this syndrome, and the potential role during treatment is an excellent point. Considering this suggestion, we reviewed the diet of this patient further with her family. We provided them a list of foods that are high in Polyamines to avoid. The patient reported in this manuscript has significant developmental delay and receives most of her nutrition through formula (Pediasure) given through gastrostomy tube. Her diet remained unchanged during the study.

We added a sentence in the methods and in the discussion on our recommendation to the family to avoid dietary items that have a high Polyamine content. “The family was provided a list of high polyamine containing food to avoid and therapy with DFMO initiated”.

3. Figure 2C would be very confusing to anyone not familiar with the ODC structure. It needs a longer explanation in either the text or the figure legend explaining that the protein is made up of two identical subunits which form to active sites at their interface. Showing the two subunits in different colors would be helpful. it is also confusing to show the two ends in different formulations without clearly explaining why this is done. The text would better if it referred to the two ODC monomers than two ODC proteins

Thank You reviewer 3, This is now done. We have changed the text to refer to monomer units, changed one of the monomers to green, and added the following sentence to clarify the structure model interpretation, “The protein in figure 2C shows one of the monomers as a surface plot in gray and the second monomer in secondary structure in green, with the region of the patient removed colored in red.” We wish to point out to the reviewers that neither of the structures mentioned contain the C-terminal amino acids, and thus we did not use either of these structures alone. To get this model we utilized a nonbiased multi model homology strategy that filled in the end regions with loop samples. We have added into the methods the following sentence: “Protein model of ODC dimer was generated using a merge of PDB files 1D7K, 2OO0, and 2ON3 with samplings of other PDB files to fill in the C-terminal region, followed by relaxation of bonds with the YASARA2 force field in a water shell using YASARA tools (www.yasara.org/).”

A reference to the structure is needed eg for human (Almrud, J. J., Oliveira, M. A., Kern, A. D., Grishin, N. V., Phillips, M. A., and Hackert, M. L. (2000) Crystal structure of human ornithine decarboxylase at 2.1 Å resolution: structural insights to antizyme binding. J. Mol. Biol. 295, 7-16 ) or mouse (Kern, A. D., Oliveira, M. A., Coffino, P., and Hackert, M. L. (1999) Structure of mammalian ornithine decarboxylase at 1.6 Å resolution: stereochemical implications of PLP-dependent amino acid decarboxylases. Structure 7, 567-581).

Please see above, Thanks.

4. A reference to the original work of the very gifted chemists and pharmacologists that lead to the conceptualization and production of DFMO would be appropriate. For example, Metcalf, B. W., Bey, P., Danzin, C., Jung, M. J., Casara, P., and Vevert, J. P. (1978) Catalytic irreversible inhibition of mammalian ornithine decarboxylase (E. C. 4. 1. 1. 17) by substrate and product analogues. J. Am. Chem. Soc. 100, 2551-2553.

The reviewer makes an excellent point that the addition of a reference to recognize the research of those who worked to make treatment with DFMO possible in the first place would add great value to the manuscript. This is now ref 6 and a sentence recognizing this work and a new citation have been added. The sentence in the introduction reads as “Eflornithine is the result of work done on developing inhibitors that lead to irreversible enzymatic inactivation of ODC from nearly forty years ago.⁶”

Author details

1. Surender Rajasekaran

   1. Pediatric Critical Care Medicine, Helen DeVos Children’s Hospital, Grand Rapids, United States
   2. Spectrum Health Office of Research and Education, Grand Rapids, United States
   3. Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, United States

   Contribution

   Conceptualization, Investigation, Project administration

   Contributed equally with

   Caleb P Bupp

   For correspondence

   surender.rajasekaran@helendevoschildrens.org

   Competing interests

   Inventor on a pending US patent (US-2020215010-A1), methods for treating or preventing developmental disorders associated with mutations in the OCD1 gene.

   "This ORCID iD identifies the author of this article:" 0000-0002-4430-006X

2. Caleb P Bupp

   1. Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, United States
   2. Medical Genetics, Spectrum Health and Helen DeVos Children’s Hospital, Grand Rapids, United States

   Contribution

   Conceptualization, Investigation

   Contributed equally with

   Surender Rajasekaran

   Competing interests

   Inventor on a pending US patent (US-2020215010-A1), methods for treating or preventing developmental disorders associated with mutations in the OCD1 gene.

3. Mara Leimanis-Laurens

   1. Pediatric Critical Care Medicine, Helen DeVos Children’s Hospital, Grand Rapids, United States
   2. Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, United States

   Contribution

   Investigation, Methodology

   Competing interests

   No competing interests declared

4. Ankit Shukla

   Department of Pharmacy, Helen DeVos Children’s Hospital, Grand Rapids, United States

   Contribution

   Methodology

   Competing interests

   No competing interests declared

5. Christopher Russell

   Spectrum Health Office of Research and Education, Grand Rapids, United States

   Contribution

   Resources, Supervision

   Competing interests

   No competing interests declared

6. Joseph Junewick

   Department of Diagnostic Radiology, Spectrum Health and Helen DeVos Children's Hospital, Grand Rapids, United States

   Contribution

   Writing - review and editing

   Competing interests

   No competing interests declared

7. Emily Gleason

   Spectrum Health Office of Research and Education, Grand Rapids, United States

   Contribution

   Resources

   Competing interests

   No competing interests declared

8. Elizabeth A VanSickle

   Medical Genetics, Spectrum Health and Helen DeVos Children’s Hospital, Grand Rapids, United States

   Contribution

   Writing - review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0001-5504-9248

9. Yvonne Edgerly

   Spectrum Health Office of Research and Education, Grand Rapids, United States

   Contribution

   Supervision

   Competing interests

   No competing interests declared

10. Bryan M Wittmann

    Metabolon, Morrisville, United States

    Contribution

    Formal analysis, Methodology

    Competing interests

    No competing interests declared

11. Jeremy W Prokop

    1. Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, United States
    2. Department of Pharmacology and Toxicology, College of Human Medicine, Michigan State University, East Lansing, United States

    Contribution

    Data curation, Investigation, Visualization

    Competing interests

    No competing interests declared

12. André S Bachmann

    Department of Pediatrics and Human Development, College of Human Medicine, Michigan State University, Grand Rapids, United States

    Contribution

    Conceptualization, Methodology, Writing - original draft, Writing - review and editing

    For correspondence

    bachma26@msu.edu

    Competing interests

    Inventor on a pending US patent (US-2020215010-A1), methods for treating or preventing developmental disorders associated with mutations in the OCD1 gene.

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