A quite broad phenotypic spectrum was observed in MTO1 mutant patients: from severe, rapidly progressive, ultimately fatal presentation in two compound heterozygous children for Arg620Lysfs*8 and Ala428Thr mutations [Ghezzi et al., 2012], to fulminant postnatal phenotype, or severe, but long-lasting, encephalo-cardiomyopathy in the two families with a homozygous p.Thr411Ile mutation (this work), to benign, compensated hypertrophic cardiomyopathy with modest neurological abnormalities in patients [Pt1 in this work; Pt3 in Ghezzi at al., 2012], bearing two missense mutations. This evidence concerns the gene MTO1 and hypertrophic cardiomyopathy.