Specific restriction fragment length polymorphism in liver mitochondrial DNA of the Chinese

By use of restriction fragment length polymorphism analysis, we examined the liver mitochondrial DNA amplified by polymerase chain reaction from 60 Chinese subjects of 31 to 78 years of age. We found nine specific mtDNA polymorphisms that had never been reported before. Eleven subjects had an Alu I polymorphic site in the subunit 2 gene of NADH dehydrogenase, five had a Hae III polymorphic site in the cytochrome oxidase subunit 2 gene, and five had a Hinf I polymorphic site in the subunit 3 gene of cytochrome oxidase. No polymorphic site was found in the structural genes coding for subunits 1, 3, 4, 4L and 6 of NADH dehydrogenase, cytochrome b, and subunit 8 of ATP synthase. Detailed analysis of the RFLP data did not show age-dependent mtDNA polymorphisms. In addition, the analysis of the restriction patterns of all the mtDNAs revealed 12 mtDNA haplotypes in all the Chinese subjects examined. Among them, type 1 mtDNA was found to be the most predominant and comprised 63.3% of the total study subjects. The restriction patterns of type 1 mtDNA generated by all restriction enzymes were identical to those deduced from the Cambridge sequence of human mtDNA. About 8.3% of the subjects exhibited type 2 mtDNA, and 5% had types 3, 5 and 8 mtDNA, respectively. Each of the rest seven mtDNA types comprised about 2% of the samples. Moreover, type 1 mtDNA was found in the platelets of three white Americans. These findings suggest that type 2 to type 12 mtDNAs have come into existence through the generation or loss of specific polymorphic restriction sites in the mtDNA of the Chinese.