A SPLICING MUTATION IN THE CYTOCHROME B(5) GENE FROM A PATIENT WITH CONGENITAL METHEMOGLOBINEMIA AND PSEUDOHERMAPHRODISM

We have analyzed reticulocyte and leukocyte mRNAs isolated from a pati ent with congenital methemoglobinemia and pseudohermaphrodism. The cyt ochrome b(5), cDNA sequences were amplified using specific oligonucleo tide primers and the polymerase chain reaction (PCR). DNA sequencing i ndicated that there was a 16-bp deletion in the cDNA leading to a new, in-frame stop signal and resulting in a truncated protein of 45 amino acids. Genomic DNA was analyzed, and the molecular lesion was shown t o be an AG-->GG alteration in the 3' splicing junction of intron 1. Th e splice site alteration leads to the usage of the nearest AG as an al ternative splice site, resulting in a 16-bp deletion in the mRNA. All of the studies on reticulocyte mRNA and genomic DNA indicated that the patient was homozygous for the lesion.