A case of methemoglobinemia type II due to NADH-cytochrome b5 reductase deficiency: determination of the molecular basis.

Clinical, biochemical and molecular findings in a patient with methemoglobinemia type II are described. Furthermore, a comparison between methemoglobinemia type I and type II, both caused by a deficiency of NADH-cytochrome b5 reductase (b5R), is made. Although the clinical pictures of type I and II are strikingly different, mutations in the diaphorase (DIA1) gene located on chromosome 22 have been described in both types. In the present patient, two newly identified mutations, both leading to a stop codon in exon 4 (Gln77Ter) and in exon 6 (Arg160Ter), were found. Identification of different mutations at different positions in the DIA1 gene might shed light on the clinical and biochemical differences between methemoglobinemia type I and type II.