Hemoglobin M Iwate is caused by a C----T transition in codon 87 of the human alpha 1-globin gene.

DNA restriction, molecular cloning, and sequencing methods have been used to characterize the mutation leading to the methemoglobinemia HbM Iwate. It could be demonstrated that the HbM Iwate defect is caused by a point mutation involving a transition from C to T in the first position of codon 87 of the alpha 1-globin gene. Furthermore, the HbM Iwate mutation can directly be identified upon RsaI digestion. This direct detection of the mutation on the gene level is of significant advantage for differential diagnostic purposes.