Methemoglobinemia is associated with oxidation of the iron in heme. Congenital hemoglobinemia is associated with a hereditary cause.
Chromosome: 22q13
Gene affected: CYB5R3
Protein affected: NADH-cytochrome b5 reductase
Types:
(1) type I: lack of cytochrome reductase activity limited to erythrocytes
(2) type II: lack of cytochrome reductase activity in all tissues
Type II may also be referred to as hemoglobin M.
Family members may be affected as well, usually with a recessive pattern of inheritance.
Clinical presentation:
(1) episodes of unexplained cyanosis (when methemoglobin level > 10%), which can occur in the neonatal period
(2) CNS (seizures, other) and/or cardiovascular symptoms (when methemoglobin level > 30%)
Differential diagnosis:
(1) acquired/toxic methemoglobinemia
