MT-CYB and histiocytoid cardiomyopathy: In 2000, Andreu et al. (2000) first identified a G to A point mutation, which was associated with a Gly to Asp substitution, at residue 15498 (OMIM516020) of the mitochondrial gene encoding cytochrome b (MTCYB) in a patient with histiocytoid cardiomyopathy.