Methemoglobinemia type II
OMIM number: 250800
Comments closing date: 27/11/2026
Methemoglobinemia type II is a very rare autosomal recessive hematologic disorder due to NADH-cytochrome b5 reductase deficiency. The enzyme normally helps maintain haemoglobin in a form capable of carrying oxygen. Affected individuals therefore have increased levels of methemoglobin and develop cyanosis (a blue/grey appearance of the skin and lips). There are two main types (type I and II). Type II is the severe form and is the type relevant to this application. People with type II have cyanosis as well as severe neurological problems. In type II, the enzyme deficiency affects the whole body,including the brain and nervous system. Patients can have severe developmental delay, intellectual disability, microcephaly, abnormal muscle tone, movement disorders and significant problems with speech and motor development. People with Methemoglobinemia type II often do not survive past early adulthood.
