Genetic studies of low-abundance human plasma proteins. XIII. Population genetics of C1R complement subcomponent and description of new variants.

Isoelectric focusing and immunoblotting reveals considerable biochemical and genetic variation in the C1R subcomponent of the first complement component. The nature of the intraindividual biochemical variation can be explained by differences in sialic acid content because after digestion with neuraminidase the terminal sialic acids are removed to yield a single major band corresponding to the C1R polypeptide. Plasma samples from a large number of different ethnic groups, consisting of U.S. whites, U.S. blacks, Nigerian blacks, and Inuit, Aleut, and Amerindian populations from the Western Hemisphere have revealed genetically determined charge variation with heterozygous phenotypes consisting of two major asialo bands, indicating that the underlying variation is not due to variation in sialic acid content. Two previously reported common alleles, C1R1 and CIR2, have been observed in all studied populations, the notable exception being the Dogrib Indian population, which is devoid of the C1R2 allele. Several new alleles--designated C1R3, C1R4, C1R5, C1R6, and C1R7-have been observed, with variable frequencies ranging from the occurrence in a single individual and related family members to the polymorphic occurrence of certain alleles in several populations. Of these new alleles, the C1R5 is of considerable interest in population and anthropological genetics studies. The C1R5 allele is widely distributed, at a frequency of .03 to .17, in all of the North American aboriginal populations screened. This allele is not present in U.S. whites but is present at a polymorphic frequency in U.S. and Nigerian blacks.(ABSTRACT TRUNCATED AT 250 WORDS)