For instance, in cases with autosomal recessive methylmalonic aciduria and homocystinuria, cobalamin C type (MAHCC; OMIM: #277400), after the identification of a genetic mutation, an epimutation at the MMACHC locus consisting of hypermethylated CpG sites, including promoter and first exon, was found secondary to splicing variants in PRDX1. The gene discussed is PRDX1; the disease is homocystinuria.