Five polymorphisms in the C6 and C7 genes have been investigated in seven ethnic groups. The allele frequencies are broadly similar in most groups except C7 M/N which is monomorphic in our group of Africans, and C6 MspI and C7 S367T where the allele frequencies in African and Cape Coloured subjects are very different from the other ethnic groups. There is very little allelic association except between C6 A/B and C6 MspI. Seventeen of the 32 possible haplotypes have been observed, suggesting that much recombination has taken place. We describe a new method for the investigation of the MspI RFLP located in intron 3 of C6 (approximately 3 kbp 3' from exon 3 and 1.5 kbp 5' from exon 4) and its molecular basis, together with an improved method for the isolation of DNA from stored serum.
The relationship between immunoglobulin allotypes and risk of developing nasopharyngeal carcinoma was examined in a comparative study of 50 Chinese cases and 140 Chinese controls and 50 Malay cases and 79 Malay controls residing in Malaysia. Although the most common Gm phenotype was elevated in both Chinese and Malay nasopharyngeal carcinoma patients compared to their controls, there were no significant differences between cases and controls in the distribution of Gm haplotypes in either population. There were no differences between cases and controls in the distribution of Km alleles in either population. Thus a previously reported association of Km(1) with increased nasopharyngeal carcinoma risk in Tunisia is not confirmed in two Mongoloid populations in Malaysia.