HLA class I variation in the West African Pygmies and their genetic relationship with other African populations

We have studied the polymorphism of HLA class I in two West African Pygmy populations, namely, the Bakola from Cameroon and the Mbenzele from the Central African Republic. A unique number of HLA alleles and haplotypes showed specific patterns of these populations. In this study, we identify two alleles (B*37, B*41) and three haplotypes (A*30-B*37, A*66-B*41 and A*68-B*58) that appear to be 'private' or typical of Western Pygmies. These data reflect similarities with the AKA Pygmies from the Central African Republic. On the other hand, we failed to identify alleles that are found at high frequencies among other sub-Saharan populations (B*42, B*51). Allelic and haplotypic frequency distributions show differences between the two Pygmy groups, e.g. B*35 was very common in the Mbenzele but has been found to be absent in the Bakola. In contrast, B*53, which is found in the Bakola, has been found to be rare in the Mbenzele Pygmies. In order to analyse the genetic relationships of the Bakola and Mbenzele Pygmies with other sub-Saharan populations, HLA gene frequencies were subjected to the Neighbour-Joining tree analysis. The Mbenzele, Bakola and AKA were found to be relatively close to each other and isolated from other sub-African populations. However, both the genetic distances and the within-group variation suggests that the Bakola are more admixed with Bantu farmers than Mbenzele.

Psoriasis vulgaris and psoriatic arthritis share a 100 kb susceptibility region telomeric to HLA-C

OBJECTIVE

To map the locus for susceptibility to psoriasis in patients with psoriatic arthritis.

METHODS

Seventy-four patients with psoriatic arthritis and 95 patients with psoriasis vulgaris were included in this study. Polymorphic genes and microsatellite markers centromeric (C1_2_5) and telomeric (C1_4_4, OTF3, HCR and the corneodesmosin gene) to HLA-C were studied in an association analysis. Typing was also performed on a control population of 104 matched donors.

RESULTS

The allele Cw*0602 was associated both with psoriasis [49 vs 21%, Pc<0.0003; odds ratio (OR)=3.6, aetiological factor (AF)=0.72] and with psoriatic arthritis (62 vs 21%, Pc<0.000001; OR=6.1, AF=0.83). In psoriatic patients a susceptibility region telomeric to HLA-C that includes C1_4_4 (56 vs 22%, Pc<0.0002; OR=4.39, AF=0.77), OTF3 (85 vs 60%, Pc<0.0002; OR=3.7, AF=0.73) and HCR (63 vs 26%, Pc<0.00001; OR=3.8, AF=0.74) was observed. In psoriatic arthritis patients the susceptibility region was delimited by HLA-C and C1_4_4 (384 allele, 56 vs 22%, Pc<0.0002; OR=4.37, AF=0.77).

CONCLUSIONS

Comparing the susceptibility regions associated with the two diseases, an overlapping interval of 100 kb between HLA-C and OTF3, which might contain the psoriasis gene, can be defined.

New insights regarding HLA-B27 diversity in the Asian population

A polymerase chain reaction-sequence-specific primer (PCR-SSP) method which distinguishes all B27 alleles described at present (B*2701-23) has been developed. The distribution of B27 alleles was characterised in six different Asian populations. HLA-B*2705, 02, 04, 07, 22 (formerly B*2706) subtypes found in Asian populations differ in their ethnic distribution, which may be the result of different genetic and geographic origins. Furthermore, two novel B27 alleles were found in this study. B*2714 was identified in two Siberians, one of whom was a patient with ankylosing spondylitis. B*2715 was found in two patients with ankylosing spondylitis in Thais. These associations have not previously been reported in either ethnic group.

Polymorphism in MICA rather than HLA-B/C genes is associated with psoriatic arthritis in the Jewish population

The aim of this study was to examine whether the association of psoriatic arthritis (PsA) with human leukocyte antigen (HLA) class I genes is secondary to linkage disequilibrium with a nearby gene. We examined a sample of the Jewish population to investigate whether HLA-B/C and DR polymorphism is associated with susceptibility, or whether other closely related class I loci, such as the major histocompatibility complex class I chain-related gene A (MICA) and tumor necrosis factor (TNF), might play a role in disease development. Comparisons of different populations with different HLA profiles would be of value in identifying the candidate genes involved in PSA. Fifty-two patients with PsA and 73 random matched controls from a Jewish population were selected and DNA typed by polymerase chain reaction-single-strand oligonucleotide probe (PCR-SSOP) (HLA-C), PCR sequence-specific primers (PCR-SSP) (HLA-B, -DR), radioactive PCR (MICA-TM polymorphism in the transmembrane region), and PCR-RFLP (TNF). Some findings can be concluded from the study: (1) the frequency of HLA-B*5701, B*3801, B*39, B*27, Cw*0602, Cw*07, DRB1*0402, and DRB1*0701 were not found to be significantly increased in PsA; (2) no significant differences of TNFalpha promoter alleles at positions -308 and -238 were found between PsA and healthy controls; (3) the trinucleotide repeat polymorphism MICA-A9 was present at a higher frequency in PsA patients, (p(c) < 0.009, RR = 3.34, EF = 0.39); and (4) MICA-A9 polymorphism was found in linkage disequilibrium with HLA-B alleles (B*5701, B*3801) described to be associated with PsA in Caucasians. These results suggest that the MICA gene or other nearby gene(s) may be involved in the development of PsA, and it would thus appear that psoriasis vulgaris (PsV) and PsA are associated with different MHC susceptibility genes.

TNF-238A promoter polymorphism contributes to susceptibility to ankylosing spondylitis in HLA-B27 negative patients

OBJECTIVE

To investigate the relative contribution of MHC loci in their susceptibility to primary ankylosing spondylitis (AS) in HLA-B27 negative patients and to compare the clinical features and genetic factors with those of HLA-B27 positive AS.

METHODS

DNA from patients with B27 negative primary AS (n = 28), B27 positive primary AS (n = 77), and matched healthy controls (B27-, n = 100; B27+, n = 70) were analyzed to investigate whether HLA genes determine the disease susceptibility, or whether other closely linked loci might play a role in disease development. HLA typing was carried out by serology and PCR/SSP (HLA-B, -DR), MICA-TM polymorphism in the transmembrane region by radioactive PCR, and tumor necrosis factor-alpha (TNF-alpha) promoter polymorphism at positions -238 and -308 by PCR-RFLP.

RESULTS

Subtle clinical differences were found for primary AS, the B27 negative patients being less frequently complicated by acute anterior uveitis and more associated with peripheral arthritis than B27 positive. Differences were found in the distribution of TNF-alpha -238 genotypes among patients with primary AS (B27- vs B27+). The TNF-alpha -238(A) polymorphism was present in 50% of the B27 negative patients carrying the -238 G/A and A/A genotypes and was significantly increased compared with B27 positive AS (odds ratio 4.3) and with the B27 negative control group (OR 5.9). The TNF-alpha genotypes were equally prevalent in B27 positive AS and healthy matched B27 positive controls. No significant HLA and MICA typing differences were found between the populations under study.

CONCLUSION

Our results indicate that the polymorphism variation in the TNF-alpha promoter -238.2(A) influences disease susceptibility in B27 negative primary AS but had no effect in our B27 positive AS population.

HLA-B27 alone rather than B27-related class I haplotypes contributes to ankylosing spondylitis susceptibility

Characterization of non-B27 susceptibility genes will be required to know the pathogenesis of AS. The aim of this study was to examine whether ankylosing spondylitis (AS) susceptibility is controlled by B27 alone rather than B27 haplotypes and, whether other closely related class I loci, such as MICA and TNFA genes might play a role in AS. Three hundred eleven B27-positive samples from Caucasoid, Asian, and African populations were selected and genotypes were carried out by PCR/SSOP (HLA-B27 and HLA-C), PCR/SSP (MICA-TM polymorphism in the transmembrane region), PCR/SSCP (MICA alleles), and PCR-RFLP (TNF-alpha). Of these, 161 were AS patients, chosen in order to investigate the contribution of TNFA and MICA loci to AS in HLA-B27 positive individuals. Some findings can be concluded from the study: (a) No significant differences of TNF-alpha promoter alleles at position -308 and -238 (A/G) were found between AS patients and B27 matched alleles from healthy controls; (b) strong linkage disequilibrium was found between the B27 and the MICA alleles. The MICA-A4 was found to be in association with B*2705,02,03 and 08; MICA-A5 with B*2704 and B*2707 and MICA-A.5.1 with B*2706; (c) no significant differences of MICA alleles were found between AS and controls carrying the B27-associated alleles, and therefore no evidence is provided for an additional role of MICA gene in AS susceptibility; (d) there are a striking correlations between the structure of B27 extended haplotypes (from MICA region to HLA-C) and the ethnic distribution of these subtypes. The results of differential linkage disequilibrium with HLA-B27 subtypes suggest that B27 itself remains the primary gene for AS susceptibility, and TNFA and MICA are not involved in the pathogenesis of the disease.

Susceptibility to ankylosing spondylitis is independent of the Bw4 and Bw6 epitopes of HLA-B27 alleles

We have characterized HLA-B27 alleles in a sample of the population from the Azores (n=46) with the aim of investigating the contribution of different subtypes to ankylosing spondylitis (AS). The study was carried out using PCR-SSOP and in some samples genomic sequencing was conducted. Some significant new finding have arisen from this study. First, B*2705,B*2702,B*2703,B*2707 and B*2708 alleles were found to be represented in this population. The polymorphism of B27 alleles found in a sample of the population from the Azores is higher than the Caucasian groups described. B*2703 and B*2707 have not previously been described to be represented in Caucasians and this could indicate admixtures with different populations of the world. In addition, the B*2708 allele was found to be associated with AS in a large family from the Azores. This association has not been previously reported in either ethnic group and needs to be confirmed in other population studies. This is of considerable interest since has only been described as a rare subtype underrepresented in the British population and has not been previously found to be associated with AS. B*2708 carries the sequence specifying the Bw6 epitope in contrast to most B27 alleles which carry a Bw4 sequence. Differences in this region (residues 77-83) can alter the F-pocket and affect T-cell recognition. The importance that these molecular changes can play in the pathogenesis of AS is discussed.