S. W. Serjeantson

DEFICIENCY OF C4A IS A GENETIC DETERMINANT OF SYSTEMIC LUPUS ERYTHEMATOSUS IN THREE ETHNIC GROUPS

Systemic lupus erythematosus (SLE) has shown associations with the major histocompatibility complex (MHC) class II DR antigens and class III complement components C2 and C4 in previous studies. The primary susceptibility locus has been difficult to identify, however, on account of linkage disequilibrium within the MHC. We have studied C4A and C4B distributions in 63 Caucasoid, 75 Chinese and 51 Japanese SLE patients. All three populations showed a statistically significant increase in C4A*Q0 (null) alleles when compared with 323 ethnically matched controls. We conclude that complete or partial deficiency of C4A is a genetic determinant of SLE common to these three ethnically distinct populations.

Genetics of diabetes in Nauru: Effects of foreign admixture, HLA antigens and the insulin-gene-linked polymorphism

SummaryGenetic factors play a major role in predisposition to diabetes in the Micronesian population of Nauru. In people aged 60 years and older, 83% of full-blooded Nauruans were diabetic compared with 17% of those with ancestral foreign admixture, as detected by HLA typing. HLA distributions also showed a small increased risk for early onset of diabetes (< 46 years) associated with HLA-Bw22 (Bw56). Variation in the restriction fragment length of DNA near the insulin gene was found, but was not associated with diabetes. The distribution in fragment lengths, previously reported in Caucasoids, was observed in healthy Polynesians, Melanesians and Micronesians.

HLA-DR,DQ sequence polymorphisms in Polynesians, Micronesians, and Javanese.

The origins of the Polynesians remain an enigma. Linguistic reconstructions of proto-Austronesian languages suggest a shared origin for Polynesians, Micronesians, and Javanese with dispersal from northern Borneo and Sulawesi. Analysis of 810 chromosomes for nucleotide sequence polymorphism at HLA-DRB1, DRB3, DRB5, DQA1, and DQB1 loci in Polynesian (Rarotonga, Western Samoa, and Niue), Micronesian (Nauru and Kiribati), and Javanese populations showed virtually no overlap of HLA class II haplotypes between contemporary Polynesians and Javanese. Further, there were marked differences in population distributions of some HLA-DRB1 alleles that could not be distinguished in earlier serologic or restriction fragment length polymorphism (RFLP) studies, e.g., for DR12, DRB1*1201 had a frequency of 15%-30% in Polynesians (1% in Micronesians and Javanese), whereas DRB1*1202 had a frequency of 28%-38% in Micronesians and 51% in Javanese (1% in Polynesians). A novel DR6-related allele, DRB1*1408, was found in all three Polynesian study populations. The Polynesian HLA class II genetic repertoire is not readily derived from the island Southeast Asian gene pool.

Characterization of the HLA-A polymorphism by locus-specific polymerase chain reaction amplification and oligonucleotide hybridization

This report describes a PCR-based typing protocol for the HLA-A polymorphism. Locus-specific primers selectively amplified HLA-A sequences from exon 1 to exon 3 in a single PCR that avoided co-amplification of other classical and nonclassical class I genes. The allelic variation in exons 2 and 3 of the HLA-A gene was examined with a set of 44 oligonucleotide probes. According to the recognized HLA-A sequences the protocol is potentially able to distinguish all known HLA-A alleles with unique nucleotide sequences in this gene region. The related HLA-A genotypes can also be identified in both homozygous and heterozygous individuals. Thus the protocol provides the highest resolution for HLA-A typing. The PCR-SSO typing technique is accurate, reliable, and particularly suitable for a large number of samples. The DNA typing results from 42 Tenth IHWS B-cell lines are compatible with the serologic and IEF definitions. Sixty-six unrelated donors from a northern Chinese population were also tested, with 16 HLA-A alleles detected. Four subtypes of HLA-A2 were found in this population. The distribution of HLA-A subtypes in the population indicated that 40% of donor-recipient pairs thought to be matched for HLA-A by serology would be mismatched. Two novel HLA-A alleles were identified by unusual oligonucleotide hybridization patterns.

The ethnic distribution of antibodies to glutamic acid decarboxylase: Presence and levels in insulin-dependent diabetes mellitus in Europid and Asian subjects

Our objective was to ascertain the frequency of antibodies to glutamic acid decarboxylase (GAD) in Europids and four Asian ethnic groups with insulin-dependent diabetes mellitus (IDDM) to gain insight into why the prevalence and incidence of IDDM varies so widely among ethnic and/or geographically diverse population groups. The subjects in this study were Europid (n = 49), Japanese (n = 16), Thai (n = 7), Korean (n = 21), and Chinese (n = 13) persons with IDDM with a duration ranging from 5 to 14 years. There were similar numbers of healthy controls matched for each ethnic group. A validated radioimmunoprecipitation assay used GAD from pig brain radiolabeled with 125I using chloramine T. Islet cell cytoplasmic antibodies measured by indirect immunofluorescence were expressed as Juvenile Diabetes Foundation units. The prevalence of antibodies to GAD, compared with Europids (63%), was much lower in all Asian populations with IDDM: Japanese (31%), Thai (29%), Korean (5%), and Chinese (27%). The mean level of antibodies to GAD, however, among diabetics from each population who gave a positive reaction, was similar. For all groups, the prevalence of antibodies to GAD was much higher than that of islet cell cytoplasmic antibodies. Almost all IDDM subjects positive for islet cell antibodies had antibodies to GAD, but the converse did not hold. A radioimmunoprecipitation assay for antibodies to GAD applied to serum from subjects with IDDM in various ethnic groups showed that Europids with IDDM had a much higher prevalence of such antibodies than did Asians. This held for all ethnic groups, and particularly Koreans. Thus, among different populations, there may be etiologic heterogeneity of IDDM.(ABSTRACT TRUNCATED AT 250 WORDS)

Diversity in HLA-DR4-related DR,DQ haplotypes in Australia, Oceania, and China.

The relative distributions of 12 HLA-DR4-related DRB1 alleles in indigenous populations of Australia, Melanesia, Micronesia, Polynesia, and northern and southern China have been determined by analysis of oligonucleotide hybridization patterns of 406 examples of HLA-DR4. DRB1*0405 and DRB1*0410 were common DR4 alleles in Australian aborigines and in Melanesians, while DRB1*0403 was the predominant DR4 allele in coastal Melanesians, Micronesians, and Polynesians; DRB1*0406 was confined to Chinese. A novel DR4 allele, found in 30% of DR4-positive Australian aborigines but exclusive to one aboriginal population, was a combination of DRB1*04 and 0803 nucleotide sequences and was carried on a haplotype with DR4-like DQ linkage arrangements. DQA1 and DQB1 typing generated 12 DR4-related haplotypes; the population distributions of these reflected the ancestral affinities of aborigines and Melanesians, the overlaying of coastal Melanesia with pre-Polynesian DR4 alleles and the colonization of Micronesia by an independent, non-Polynesian group. DR4-related autoimmune disorders such as rheumatoid arthritis (RA) and insulin-dependent diabetes mellitus (IDDM) are virtually unknown in indigenous populations of Australia and Oceania and this study confirmed that high-risk RA determinants, Dw4 and Dw14, occurred rarely. However, the DQw8 allele, thought particularly to predispose to IDDM, was present in the majority of DR4-positive Polynesians and Micronesians.

HLA-DRβ gene DNA polymorphisms revealed by Taq I correlate with HLA-DR specificities

Human genomic DNA digested with restriction endonuclease Taq I was hybridized with cDNA probes for DR beta and DQ beta, for correlation of restriction fragment length polymorphisms with HLA-DR specificities. DR beta Taq I RFLPs were distinctive for DR serological types 1 to w9, with the exception of DR3 and w6, and were markedly consistent within DR specificity. Some common variants in RFLPs did emerge within serological type; DR3, e.g., was associated with two different fragment patterns, one of which occurred on the A1.B8.DR3 haplotype and was linked with a DR alpha Bgl II variant, and the other on the B18.DR3 haplotype. In the Pacific specimens examined, RFLPs were, with few exceptions, similar to those seen in Caucasoids sharing the same DR specificity. This study indicates that genomic hybridization is a useful adjunct to serological and cellular class II typing and should be particularly informative in identifying new HLA-DR alleles in populations serologically less well-defined than Caucasoids.

Variable gene usage of T cell receptor γ‐ and δ‐chain transcripts expressed in synovia and peripheral blood of patients with rheumatoid arthritis

The synovial tissue and fluid of patients with rheumatoid arthritis (RA) contain activated T cells that probably have a central role in the disease process which leads to joint destruction. A subset of T cells, γδ T cells detected at the site of inflammation, may be important in the pathogenesis of the disease. This study investigated variable (V) gene usage of γδ T cell receptors (TcRs) expressed in synovia and peripheral blood of patients with RA by using the polymerase chain reaction (PCR) to amplify TcR γ‐and γ‐chain transcripts. Most patients showed no restriction in Vγ gene usage since synovial mononuclear cells (SMC) expressed TcR γ‐chain transcripts which used the same set of Vγ genes as peripheral blood mononuclear cells (PBMC). In contrast, the majority of patients expressed a restricted SMC Vδ‐chain repertoire biased towards Vδ1, but Vδ2 mRNA transcripts were also detected, albeit at low levels in some patients. The TcR δ‐chain repertoires of PBMC from healthy control subjects were also characterized. There was variation in the TcR δ‐chain repertoires of PBMC from patients when compared with controls, particularly with respect to expression of Vδ4. Vδ4 mRNA transcripts were expressed in PBMC of only two of seven RA patients in contrast with eight of the nine controls (P=0.03). These findings are compatible with reports that γδ T cells in the rheumatoid synovium are reactive to Mycobacterium tuberculosis and that response to M. tuberculosis is restricted to VγL9/Vδ2‐bearing T cells, if a superantigen is involved in the pathogenesis of RA.

A genetic marker at the glucokinase gene locus for Type 2 (non-insulin-dependent) diabetes mellitus in Mauritian Creoles

SummaryThe prevalence of Type 2 (non-insulin-dependent) diabetes mellitus is high in Mauritius, a multiethnic island nation in the southwestern Indian Ocean. Evaluation of candidate genes in the different ethnic groups represents a means of assessing the genetic component. As glucokinase is known to be a key regulator of glucose homeostasis in liver and pancreatic Beta-cells, the human gene was isolated and a dinucleotide repeat (CA)n marker was identified at this locus. A polymerase chain reaction assay was developed, and alleles differing in size were observed in individuals, according to the number of repeats in the amplified fragment. Eighty-five Creoles and 63 Indians of known glucose tolerance status were typed by amplification of genomic DNA for this dinucleotide (CA)n repeat marker. Four different alleles were observed including Z, the most common allele, and Z+2, Z+4, and Z+10, which differed from Z by 2, 4, and 10 nucleotides respectively. In Mauritian Creoles, the frequency of the Z+2 allele was greater in Type 2 diabetic subjects than in control subjects (23.8 % vs 8.9 %, p=0.008), and the frequency of the Z allele was lower in Type 2 diabetic subjects (60% vs 75.6%, p=0.03). Analysis with univariate logistic regression models indicated that the Z+2 allele had the highest odds ratio, 3.08 (95% confidence interval 1.14–8.35, p=0.0416), among the other risk factors (age, sex, body mass index, and waist/hip ratio). The multivariate odds ratio for Type 2 diabetes was 2.88 (95% confidence interval 0.98–8.50, p=0.0551). In contrast, in the Mauritian Indian population, no differences were noted between the frequency of any glucokinase allele in the Type 2 diabetic and control groups. These data suggest that the Z+2 allele is an important risk factor for Type 2 diabetes in Mauritian Creoles, but not in Mauritian Indians, and also imply that the glucokinase gene may play a role in the pathogenesis of Type 2 diabetes in Mauritian Creoles. Further studies are needed to define the nature of this defect.

HLA and Susceptibility to Leprosy

This review examines the evidence for involvement of MHC-associated factors in host immune response to Mycobacterium leprae, by collating HLA studies of sporadic and familial leprosy and discussing possible HLA-related immunological mechanisms in determining host response. Formal linkage analysis of 109 multiple-case families with data available for HLA haplotype segregation showed that under a three-allele recessive model for susceptibility to leprosy, linkage was observed between the HLA complex and a leprosy susceptibility locus at a recombination fraction of 20%. The significance of the linkage relationship was confined to families with at least two tuberculoid leprosy offspring and neither parent affected. When one parent was affected, with leprosy of any clinical type, lod scores could neither implicate nor exclude linkage between HLA and leprosy susceptibility and this apparent paradox can be explained by the presence of an additional, non-HLA linked susceptibility locus for leprosy.