The distribution of HL-A antigens in the coastal populations of Papua New Guinea

A high incidence of polymorphic CYP2C19 variants in archival blood samples from Papua New Guinea

There is considerable inter-ethnic variability in the incidence of CYP2C19 genetic poor metabolisers (var/var). About 3 per cent of Caucasians are CYP2C19 var/var. By contrast, an extremely high incidence (70 per cent) is observed in the Melanesian island of Vanuatu. The colonisation of the Pacific Islands is believed to have involved migration through Papua New Guinea (PNG), and hence a high incidence may also be expected in this population. The reported incidence in PNG was only 36 per cent, however. PNG is a country of extensive ethnic diversity, and the incidence of the CYP2C19 var/var in other regional populations of PNG is currently not established. In this study, restriction fragment length polymorphism-polymerase chain reaction analysis of archival blood serum samples was used to determine the prevalence of the CYP2C19*2 and *3 variant alleles in three different ethnic and geographically isolated populations of PNG. In the largest population studied (Iruna), the frequency of both variant CYP2C19 alleles was high (0.37 and 0.34, respectively). Specifically, the frequency of the CYP2C19*3 allele was significantly higher than in the PNG (East Sepik) population reported previously (0.34 vs 0.16; p <0.0001). In the Iruna population, 48.9 per cent of the samples were homozygous variants for CYP2C19*2 or *3, which although higher was not statistically different from the East Sepik population (36 per cent). The results of this study indicated that other regional populations of PNG also have a relatively high incidence of the CYP2C19 genetic polymorphism compared with Caucasian populations. The high incidence reported in Vanuatu, however, may be due to genetic drift rather than a PNG founder population, as the Vanuatu population is dominated by the CYP2C19*2 allele, with a lower contribution from the *3 allelic variant.

Antigen and haplotype frequencies at three human leucocyte antigen loci (HLA-A, -B, -C) in the Pawaia of Papua New Guinea

The genetic profile of the Pawaia, a seminomadic, linguistic isolate from the highlands fringe of Papua New Guinea, is described in terms of antigen and haplotype frequencies at three class I human leucocyte antigen loci (HLA-A, -B, and -C). The Pawaia, like other Papua New Guinea populations, exhibit restricted polymorphisms at all three loci studied, both in the number of alleles segregating and in the level of average heterozygosity. An extremely high frequency (52.9%) of HLA-B27, the antigen implicated in the pathogenesis of seronegative arthropathies, was found. A novel HLA-C locus specificity, CNG, resulting probably from a gene duplication event, was also observed in significant numbers. Although the gene frequency comparisons suggest their strong affinities with the highlanders, the Pawaia haplotypes reveal significant admixture from other neighbouring groups as well. The usefulness of HLA haplotypes in tracing the movements of human populations in the New Guinea area is discussed.

HLA studies of Highland and Coastal New Guineans

The HLA profile of three New Guinean populations, two Highland (Asaro, Watut), and one Coastal is presented. The Highland populations are characterized by a low average number of alleles segregating at the HLA loci and also by a low mean value of heterozygosity at these loci. The genetic affinities of the two Highland groups with other Melanesian populations in the Pacific are remote. The Coastal group, on the other hand, shows strong similarities in its antigenic diversity and haplotypic combinations with other Melanesian populations. Nonetheless, the two Highland groups show significant divergence from each other in terms of allelic and haplotypic frequencies. Two different waves of migration settled in the Highlands of New Guinea between 10,000 and 15,000 years ago, and it is possible that the Watut, an Angan speaking group, represents the remnants of the first migration into the interior, whereas the Asaro, members of the Eastern Central family of the Trans-New Guinea phylum, arrived at a later date.

Type 2 (non-insulin-dependent) diabetes mellitus and HLA antigens in Papua New Guinea

HLA phenotypes were studied in 57 Type 2 (non-insulin-dependent) diabetic Papuan patients and the results compared with control subjects of the same Austronesian origin. An association was found between disease and BW62, a split antigen of B15, with corrected probability significant at the 5% level. The frequencies of B13 and BW22 were also increased in diabetic patients but the differences were not statistically significant. Although it has been postulated that Melanesian communities have protection against diabetes, they have a high frequency of BW62, which would imply, from the association found in this study, that susceptibility to Type 2 diabetes has yet to become manifest in them.

HLA-A,B,C and DR antigens in Asaro speakers of Papua New Guinea

The HLA profile of the Asaro speakers of Papua New Guinea exhibits restricted polymorphisms. Antigens like AW24, MT1, and MB1 were present in almost every individual assayed. A CW6-related antigen and a DR locus antigen FT19 (a split of DRW6), not previously found in Pacific populations, were observed in a significant number of individuals. Ancestral HLA-B,C haplotypic combinations, such as B13, CW4 and BW60,CW3, were frequently found. Preliminary evidence is provided for an association between BW62 and CW65 in this population. The observed distributions of multiple-locus heterozygosities are similar to those expected under the null hypothesis of linkage equilibrium. The results indicate that the Asaro, among other highland populations, have been isolated long enough for pre-existing linkage disequilibria at recombinational distances of 0.8% or more (such as occur with HLA-A,B and HLA-B,DR haplotypes) to have broken down.

HLA antigens in four Pacific populations with non-insulin-dependent diabetes mellitus

HLA antigen distributions in persons with normal and abnormal glucose tolerance were compared in four Pacific populations. The populations included Melanesians from the Fijian Islands, Loyalty Islands and mainland New Caledonia and Polynesians from the Wallis Islands. HLA-DR results are provided for the first time for Pacific groups. In Polynesians, HLA-B22 was increased in frequency in patients with non-insulin-dependent diabetes mellitus and also in persons with impaired glucose tolerance. However, the association was not statistically significant when corrected for the number of antigens tested. A similar increase in HLA-B22, although not significant, was seen in each of the three Melanesian populations with abnormal glucose tolerance. No other consistent increase in any HLA antigen occurred in persons with abnormal plasma glucose concentrations.