Susceptibility to AS is largely genetically determined, and the environmental trigger for the disease is probably ubiquitous. HLA-B27 accounts for a minority of the overall genetic susceptibility to AS.

Summary. People with genetic haemochromatosis (GH) accumulate iron from excessive dietary absorption. In populations of northern European origin, over 90% of patients are homozygous for the C282Y mutation of the HFE gene. While about 1 in 200 people in the general population have this genotype the proportion who develop clinical haemochromatosis is not known. The influence of HFE genotype on iron status was investigated in 10 556 blood donors. The allele frequencies of the C282Y and H63D mutations were 8´23% and 15´3% respectively. Heterozygosity for C282Y occurred in 1 in 7´9 donors, for H63D in 1 in 4´2 donors, and 1 in 42 were compound heterozygotes. Homozygosity for H63D occurred in 1 in 42 donors and 1 in 147 (72) were homozygous for C282Y. Mean values increased for transferrin saturation (TS) and serum ferritin (sFn), and decreased for unsaturated iron binding capacity (UIBC) in the order: donors lacking the mutations, H63D heterozygotes, C282Y heterozygotes, H63D homozygotes, compound heterozygotes and C282Y homozygotes, but serum ferritin (sFn) concentrations were no higher in H63D heterozygotes and C282Y heterozygous women than in donors lacking mutations. The percentage of donors failing the screening test for anaemia or of those with sFn , 15 mg/l did not differ among the genotype groups. C282Y and H63D heterozygotes and donors homozygous for H63D were at no greater risk of iron accumulation than donors lacking mutations, of whom 1 in 1200 had both a raised TS and sFn. The risk was higher for compound heterozygotes (1 in 80, P 0´003) and for C282Y homozygotes (1 in 5, P , 0´0001). There was no correlation between sFn and either age or donation frequency in C282Y homozygotes. None of the 63 C282Y homozygous donors interviewed showed physical signs of overload or were aware of relatives with haemochromatosis. The Welsh Blood Service collects blood from about 140 000 people each year including an estimated 950 who are homozygous for HFE C282Y. They are probably healthy and unaware of any family history of iron overload.

Objective-To investigate the HLA class I associations of ankylosing spondylitis (AS) in the white population, with particular reference to HLA-B27 subtypes. Methods-HLA-B27 and -B60 typing was performed in 284 white patients with AS.

Accurate estimates of HLA-A, B, DR and DQ phenotype, gene and haplotype frequencies (HF) in the normal population are of importance in, for example, disease susceptibility studies, platelet transfusion support and transplantation. HLA population genetics studies have been performed on numerous groups, however, no major studies have been carried out on the population of Wales. As part of the validation process for our routine HLA-A and B typing by PCR using sequence-specific primers (PCR-SSP) we examined 1,798 normal, unrelated Caucasoid blood donors living in Wales and recruited onto the Welsh Bone Marrow Donor Registry (WBMDR). Typing was performed by serology (HLA-A, B) and PCR-SSP at low resolution (HLA-A, B, DR, DQ) resulting in a particularly rigorous level of HLA specificity assignment. Four discrepancies were found between the HLA-A and B serological and PCR-SSP specificity assignments: (1) two instances of HLA-A2 by serology were undetected by PCR-SSP and were a new HLA-A2 allele – A*0224; (2) one example of HLA-B*15 by PCR-SSP failed to react by serology, and remained undetectable by serology in subsequent samples, and (3) one example of HLA-B45 by serology was identified as HLA-B*5002 by PCR-SSP. Hardy-Weinberg and homozygosity analysis showed that the goodness-of-fit was excellent (p > 0.05), for both phenotype distribution and the number of homozygotes identified, for all four loci. The phenotype and gene frequencies for the 18 HLA-A, 34 -B, 15 -DR and 8 -DQ specificities identified and two- and three-locus HF, linkage disequilibrium and related values for HLA-A/B, B/DR, DR/DQ and HLA-A/B/DR and B/DR/DQ were essentially typical of a northern European population. HLA-A2, B44, DR4 and DQ2 were the highest frequency phenotypes and HLA-A2403, A34, A74, B42, B75, B2708, B48, B67 and B703 occurred once only. There were no examples of: A36, A43, A69, A80, B46, B54, B59, B73, B76, B77, B7801, B8101 or DR18 specificities. DR17, DQ2 and A1, B8, DR17 were the highest frequency two- and three-locus haplotypes identified. Diverse HLA-A, B, DR phenotypes were identified in 87.0% (1,564) of subjects. When HLA-DQ was also considered, different four locus phenotypes were identified in 89.1% (1,602) of subjects. This frequency information will be beneficial as a high-quality reference control for disease susceptibility studies and in calculating the chances of identifying a bone marrow donor in a patient’s extended family. This process was successful for the validation of our HLA-A and -B PCR-SSP typing procedure and the findings suggest an accurate level of specificity assignment of WBMDR panel donors who had previously been typed by serology alone.

We examined HLA-DR genotype risk in 288 patients with rheumatoid arthritis who were carefully categorized for disease severity. Five hundred ethnically-matched bone-marrow donors were controls. A hierarchy of positive allelic associations was noted with DRB1*0401 (p < 10(-38), *0404,8 (p < 10(-43), *0405 (p < 10(-8), *10 (p < 10(-3) and *0101,2 (p < 10(-2), while DRB1*0403 was negatively associated (p = 0.02). The DRB1 genotype relative risks (and 95% CIs) for RA were: *0404,5,8/*0404,5,8 = 36.2 (15-87), *0401/*0404,5,8 = 31.3 (18-55), *401/*0401 = 18.8 (11-35), *0101,2/*0404,5,8 = 6.0 (2-14), *0101,2/*0401 = 6.4 (3-12), *0101,2/*0101,2 = 1.3 (0.3-6), *10/*0404,5,8 = 27.8 (5-148), *10/*0401 = 20.8 (5-89), *10/*0101,2 = 22.3 (5-96), *0404,5,8/DRX = 5.0 (3-8), *0401/DRX = 4.7 (3-7), *0101,2/DRX = 2.3 (1.4-4), *10/DRX = 3.4 (0.8-14). No significant correlation of DRB1 genotypes was found with severity of RA as judged by nodules or articular erosions.

The Major Histocompatibility Complex (MHC) class I chain related (MIC) A and B genes are important additional loci within the MHC. We have developed a MICA and MICB typing system using the polymerase chain reaction with sequence-specific primers (PCR-SSP), which operates under the same conditions as our routine HLA-A, -B, and -C typing method. We designed 95 primers in 84 SSP mixtures for MICA and 39 primers in 29 mixtures for MICB. This detected and differentiated all 55 MICA and 19 MICB alleles (except MICA*00701 from MICA*026, MICA*00201 from MICA*020, and three MICB alleles, which are intronic variations). A computer program confirmed the MICA amplification reactivity of each SSP mixture and evaluated the typing set for MICA allele combination ambiguities. Seventy-six "reference" DNA samples were used for validation: 50 from International Histocompatibility Workshop B lymphoblastoid cell lines (IHW BCLs) and 26 MICA-typed samples from two laboratories. The reference material identified 28 out of the 55 MICA alleles and 13 of the 19 MICB alleles, and directly validated 62 of the 84 MICA and 20 of the 29 MICB SSP mixtures. Our genotyping agreed with 283 out of the 286 (98.95%) MICA and MICB reference laboratories' allele assignments or the consensus assignments. Two of the discrepancies remain unresolved, whereas one was probably due to a reference laboratory's failure to differentiate alleles differing in exon 5 of the MICA gene. A comparison of the MICA and MICB allele assignments between laboratories identified a "disagreement rate" of 19.4% for MICA alleles and 13.1% for MICB alleles. Accordingly, we have compiled "consensus" MICA and MICB genotypes for the 50 IHW BCLs tested, which have been confirmed by our typing. We also typed 166 random blood donors. Their MICA and MICB carriage and allele frequencies and HLA-B, MICA, MICB linkage disequilibrium parameters and haplotype frequencies largely concurred with other published data on United Kingdom subjects, further supporting the validity of our typing system. This PCR-SSP system is a simple, reliable and rapid technique for typing MICA and MICB alleles. It is easily updated as new alleles are identified but clearly requires a continuing validation review until all known MICA and MICB alleles have been identified.

No abstract

Objective. We have previously identified a singlenucleotide polymorphism (SNP) haplotype involving the lymphotoxin ␣ (LTA) and tumor necrosis factor (TNF) loci (termed haplotype LTA-TNF2) on chromosome 6 that shows differential association with rheumatoid arthritis (RA) on HLA-DRB1*0404 and *0401 haplotypes, suggesting the presence of additional non-HLA-DRB1 RA susceptibility genes on these haplotypes. To refine this association, we performed a case-control association study using both SNPs and microsatellite markers in haplotypes matched either for HLA-DRB1*0404 or for HLA-DRB1*0401.Methods. Fourteen SNPs lying between HLA-DRB1 and LTA were genotyped in 87 DRB1*04-positive families. High-density microsatellite typing was performed using 24 markers spanning 2,500 kb centered around the TNF gene in 305 DRB1*0401 or *0404 cases and 400 DRB1*0401 or *0404 controls. Single-marker, 2-marker, and 3-marker minihaplotypes were constructed and their frequencies compared between the DRB1*0401 and DRB1*0404 matched case and control haplotypes.Results. Marked preservation of major histocompatibility complex haplotypes was seen, with chromosomes carrying LTA-TNF2 and either DRB1*0401 or DRB1*0404 both carrying an identical SNP haplotype across the 1-Mb region between TNF and HLA-DRB1. Using microsatellite markers, we observed two 3-marker minihaplotypes that were significantly overrepresented in the DRB1*0404 case haplotypes (P ‫؍‬ 0.00024 and P ‫؍‬ 0.00097).Conclusion. The presence of a single extended SNP haplotype between LTA-TNF2 and both DRB1*0401 and DRB1*0404 is evidence against this region harboring the genetic effects in linkage disequilibrium with LTA-TNF2. Two RA-associated haplotypes on the background of DRB1*0404 were identified in a 126-kb region surrounding and centromeric to the TNF locus.