Molecular mechanism of recessive congenital methemoglobinemia in Chinese pedigrees

Objective To investigate the molecular mechanism of recessive congenital me themoglobinemia (RCM) in Chinese and to establish a gene diagnostic method of polymerase chain reaction- restricted fragment length polymorphism (PCR- RFLP). Methods Total RNA was isolated from the peripheral leukocytes of the propos itus and b5R cDNA synthesized by reverse transcription-polymerase chain rea ction (RT-PCR). The coding region of b5R cDNA was analyzed by sequencing of the RT-PCR products. Results Both propositi A and B were found to be homozygotes for a G to A tr ansition at codon 57 in exon 3, changing a guanine to an adenine. This poin t mutation was not an artificial occurrence during polymerase chain reactio n (PCR), as confirmed by Msp I restriction enzyme analysis of the genomic D NA. Propositus A's mother and propositus B's sister and her nephew were fou nd to be heterozygotes for the mutation. Conclusion A guanine-to-adenine transition at codon 57, replacing arginine with glutamine, was the molecular basis for RCM in two Chinese families.