Abstract
The glutamate pyruvate transaminase 2 (GPT2) gene produces a nuclear-encoded mitochondrial enzyme that catalyzes the reversible transfer of an amino group from glutamate to pyruvate, generating alanine and alpha-ketoglutarate. Recessive mutations in GPT2 have been recently identified in a new syndrome involving intellectual and developmental disability (IDD), postnatal microcephaly, and spastic paraplegia. We have identified additional families with recessive GPT2 mutations and expanded the phenotype to include small stature. GPT2 loss-of-function mutations were identified in four families, nine patients total, including: a homozygous mutation in one child [c.775T>C (p.C259R)]; compound heterozygous mutations in two siblings [c.812A>C (p.N271T)/c.1432_1433delGT (p.V478Rfs*73)]; a novel homozygous, putative splicing mutation [c.1035C>T (p.G345=)]; and finally, a recurrent mutation, previously identified in a distinct family [c.1210C>T (p.R404*)]. All patients were diagnosed with IDD. A majority of patients had remarkably small stature throughout development, many < 1st percentile for height and weight. Given the potential biological function of GPT2 in cellular growth, this phenotype is strongly suggestive of a newly identified clinical susceptibility. Further, homozygous GPT2 mutations manifested in at least 2 of 176 families with IDD (approximately 1.1%) in a Pakistani cohort, thereby representing a relatively common cause of recessive IDD in this population, with recurrence of the p.R404* mutation in this population. Based on variants in the ExAC database, we estimated that approximately 1 in 248 individuals are carriers of moderately or severely deleterious variants in GPT2.
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Acknowledgements
The authors would like to thank the families for their participation in the current study.
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Research reported in this publication was supported in part by the following: National Institute of Mental Health grant numbers R01MH102418 and R01MH105442 and the Hassenfeld Child Health Innovation Institute at Brown University (EMM); Canadian Institutes of Health Research grant numbers MOP-102758 and PJT-156402 (JBV); and a Carney Institute for Brain Science and Suna Kıraç Fellowship Graduate Award in Brain Science (OB).
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Ouyang, Q., Kavanaugh, B.C., Joesch-Cohen, L. et al. GPT2 mutations in autosomal recessive developmental disability: extending the clinical phenotype and population prevalence estimates. Hum Genet 138, 1183–1200 (2019). https://doi.org/10.1007/s00439-019-02057-x
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DOI: https://doi.org/10.1007/s00439-019-02057-x