CYCS-related thrombocytopenia in three Japanese families with a novel variant in one family.

CYCS encodes somatic cytochrome c, which plays a central role in the electron transport chain and oxidative phosphorylation. We report nine cases of autosomal dominant, non-syndromic CYCS-related thrombocytopenia in three Japanese families. Patients showed no or mild bleeding tendency, with preserved platelet size and morphology, and without other abnormalities in blood cell lineages. Using targeted gene sequencing for congenital thrombocytopenia, we identified pathogenic missense variants in CYCS, shared by all affected individuals in each family. Two were previously reported: c.274A > G,p.(Arg92Gly) and c.309C > T,p.(Thr103Ile); one was novel: c.212A > C,p.(Asn71Thr). Genetic testing should be considered in unexplained familial thrombocytopenia.