Hereditary methaemoglobinaemia (Q39674)

Hereditary methemoglobinemia (HM) is a rare red cell disorder classified principally into two clinical phenotypes: autosomal recessive congenital (or hereditary) methemoglobinemia types I and II (RCM/RHM type 1; RCM/RHM type 2). In RCM type 1, well-tolerated cyanosis from birth is the only symptom. RCM type 2, with global loss of Cb5R function, is much more severe; the cyanosis is accompanied by neurological dysfunction (with intellectual deficit, microcephaly, growth retardation, opisthotonus, strabismus and hypertonia), which usually becomes evident during the first four months of life.