Hemoglobins M: Five different mutations of hemoglobin (Hb) are
known to produce congenital methemoglobinemia: Hb MBoston, Hb
MIwate, Hb MSaskatoon, Hb MHyde Park, and Hb MMilwaukee.
Congenital Deficit in NADH-Cytochrome b5 Reductase: Two types: type I in which the deficit is limited to the red blood cells,
and type II in which the deficit is generalized (brain, liver, muscle,
etc.). In red blood cells, the enzyme is present in its soluble form and is
responsible for reversing the spontaneous oxidation of hemoglobin to
methemoglobin. In other cells, it is located in the membrane of many
organelles (Golgi system, microsomes, mitochondria) and is involved in the
recycling of vitamin E and in the synthesis of cholesterol and cerebral
lipids.