Adult case of 17β-hydroxysteroid dehydrogenase type 10 (HSD10) deficiency due to the p. Arg130Cys mutation of the

Background: HSD10 mitochondrial disease (HSD10MD) is a rare X-linked disorder caused by pathogenic variants in the Case Description: We describe a 49-year-old French male presenting with hypertrophic cardiomyopathy, intellectual disability, psychomotor delay, stereotypies, and epilepsy. Developmental delay was noted after 18 months, and the first seizure occurred at age 14 years, followed by a prolonged coma. Cardiac evaluation revealed left ventricular hypertrophy, dilation, and left ventricular ejection fraction of 45%. Neurodevelopmental features included behavioral disturbances, echolalia, and inability to acquire literacy. Genetic testing initially identified no abnormalities, but exome sequencing revealed a pathogenic Conclusions: This case underscores the clinical variability of HSD10MD and highlights the diagnostic importance of genetic testing, particularly in adults with atypical or milder phenotypes. The association of hypertrophic cardiomyopathy with HSD10MD, as demonstrated here, suggests that cardiac involvement can dominate the clinical picture in some cases. The role of somatic mosaicism in moderating disease severity warrants further exploration. This report contributes to the limited literature on adult presentations of HSD10MD and expands the phenotype associated with the p. Arg130Cys mutation.