Propylthiouracil and carbimazole associated-antineutrophil cytoplasmic antibodies (ANCA) in patients with Graves' disease

OBJECTIVE

Propylthiouracil treatment of Graves' disease has been postulated to provoke antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. We aimed to investigate whether carbimazole therapy was also associated with increased risk of ANCA.

DESIGN

The occurrence of ANCA and the relationship to thionamide treatment was investigated in a cross-sectional study in a consecutive series of 407 patients' with Graves' disease, 200 with Hashimoto's thyroiditis and 649 normal euthyroid subjects.

MEASUREMENTS

ANCA was measured by indirect immunofluorescence (IIF) and enzyme-linked immunosorbent assay (ELISA) for proteinase 3 and myeloperoxidase-ANCA.

RESULTS

The prevalence of ANCA, as measured by IIF, was increased in the Graves' disease cohort (19.9%) compared with euthyroid controls (4.6%; P < 0.001). The prevalence of MPO-ANCA (measured by ELISA) was also increased in Graves' disease (P = 0.019). ANCA prevalence was more strongly associated with propylthiouracil treatment than carbimazole (P = 0.0265), although risk of ANCA was also higher in Graves' patients treated with carbimazole than controls (RR 2.2, P < 0.0001). ANCA positivity was not increased in patients with Hashimoto's thyroiditis.

CONCLUSION

This study revealed a high prevalence of ANCA in treated patients with Graves' disease but not in those with Hashimoto's thyroiditis. Furthermore, within the Graves' disease population, ANCA development was associated with propylthiouracil usage to a greater extent than carbimazole. These findings suggest that the altered immune environment associated with autoimmune thyroid disease is not sufficient to develop ANCA but treatment with thionamides is important in promoting ANCA development.

Haplotype tagging for the identification of common disease genes

Genome-wide linkage disequilibrium (LD) mapping of common disease genes could be more powerful than linkage analysis if the appropriate density of polymorphic markers were known and if the genotyping effort and cost of producing such an LD map could be reduced. Although different metrics that measure the extent of LD have been evaluated, even the most recent studies have not placed significant emphasis on the most informative and cost-effective method of LD mapping-that based on haplotypes. We have scanned 135 kb of DNA from nine genes, genotyped 122 single-nucleotide polymorphisms (SNPs; approximately 184,000 genotypes) and determined the common haplotypes in a minimum of 384 European individuals for each gene. Here we show how knowledge of the common haplotypes and the SNPs that tag them can be used to (i) explain the often complex patterns of LD between adjacent markers, (ii) reduce genotyping significantly (in this case from 122 to 34 SNPs), (iii) scan the common variation of a gene sensitively and comprehensively and (iv) provide key fine-mapping data within regions of strong LD. Our results also indicate that, at least for the genes studied here, the current version of dbSNP would have been of limited utility for LD mapping because many common haplotypes could not be defined. A directed re-sequencing effort of the approximately 10% of the genome in or near genes in the major ethnic groups would aid the systematic evaluation of the common variant model of common disease.

HLA typing and immunological characterization of young-onset diabetes mellitus in a Hong Kong Chinese population

AIMS

A study of the Hong Kong Chinese showed that the majority of subjects with young-onset diabetes (age of diagnosis < 35 years) present with a phenotype suggestive of Type 2 diabetes mellitus, although up to 50% subsequently need insulin treatment. The aim of this study was to use a combination of clinical, genetic and immunological markers to characterize the disease phenotype further in such individuals and to determine whether the requirement for insulin is the result of autoimmune disease.

METHODS

One hundred and thirty-seven Hong Kong Chinese with young-onset diabetes were studied, irrespective of their mode of presentation. The subjects were typed for alleles of the HLA-DR and -DQ genes and investigated for the presence of autoantibodies to glutamic acid decarboxylase (GAD). Plasma C-peptide concentration and requirement for insulin were also determined.

RESULTS

One hundred and three subjects presented with a syndrome resembling Type 2 diabetes, while 34 presented with Type 1 diabetes. Of the former group, 35 patients (34.0%) were insulin-deficient, 16 (15.5%) were insulin-treated and seven (6.9%) were positive for GAD autoantibodies. Among the GAD-positive subjects presenting with Type 2 diabetes, the HLA-DRB1*03 allele may be a marker of early progression to insulin therapy.

CONCLUSIONS

Seven subjects with Type 2 diabetes at presentation had autoantibodies to GAD. Causes other than GAD autoimmunity, however, must be sought to explain the high prevalence of insulin deficiency observed in the Chinese patients. This study highlights the heterogeneity of the pathogenic processes leading to the diabetic phenotype.

The A-G polymorphism in exon 1 of the CTLA-4 gene is not associated with systemic lupus erythematosus

OBJECTIVES

Factors contributing to the development of systemic lupus erythematosus (SLE) remain largely unknown although are likely to include both environmental and genetic components. Studies on murine lupus have indicated a role for an antibody that blocks binding of cytotoxic T lymphocyte associated-4 (CTLA-4) to B7 on antigen presenting cells in the treatment of disease, suggesting that CTLA-4 may play an important part in the disease process. This study, therefore, investigated the frequency of a previously described A-G polymorphism in exon 1 of the CTLA-4 gene, the G allele of which has shown to be associated with both Graves' disease and type I diabetes, to determine whether this polymorphism was playing a part in the development of SLE.

METHODS

One hundred and twenty six SLE patients and 363 control subjects were genotyped for the A-G polymorphism in exon 1 of the CTLA-4 gene. Target DNA was amplified using the polymerase chain reaction and the resulting product was digested using the BbvI restriction enzyme.

RESULTS

No differences in allele or genotype frequencies were observed between patients with SLE and control subjects.

CONCLUSION

These data suggest that the A-G polymorphism in exon 1 of the CTLA-4 gene does not play a part in the genetic susceptibility to the development of SLE.

The insulin gene region and susceptibility to insulin-dependent diabetes mellitus in four races; new insights from Afro-Caribbean race-specific haplotypes

The IDDM2 component of the genetic susceptibility to insulin-dependent diabetes mellitus (IDDM) has been mapped to chromosome 11p15.5. The exact identity of IDDM2 remains uncertain. It has been suggested that IDDM2 maps within the 5' VNTR (variable number tandem repeat) polymorphism upstream of the insulin gene (INS). This has not been confirmed and a contribution from other INS gene region polymorphisms cannot be excluded. We present INS region genotype data from four racial groups: the Japanese, Hong Kong Chinese, North Indian Asians and Afro-Caribbeans (two groups; one born and resident in the UK, one in Jamaica). These races have not been previously studied with the range of INS region polymorphisms included here. No INS polymorphism was associated with IDDM across all races. These data from this study thus do not identify any INS polymorphism as IDDM2. The Afro-Caribbean race showed a very different distribution of INS genotypes from the other races and novel race-specific INS haplotypes were identified. Analysis of these excluded a contribution to susceptibility to IDDM from the- 23HphI INS polymorphism. An Afro-Caribbean INS haplotype which differed only at the VNTR from the very protective INS haplotype (VPH) identified in white Caucasians was detected. Population analysis of this haplotype will allow direct assessment of the role of the VNTR in susceptibility to IDDM. In conclusion, the diverse Afro-Caribbean TH/INS/IGF2 haplotypes identified in this study will be valuable in mapping IDDM2 more precisely.

Genetic susceptibility to the development of autoimmune disease

1. Autoimmune diseases are common conditions which appear to develop in genetically susceptible individuals, with expression of disease being modified by permissive and protective environments. Familial clustering and data from twin studies provided the impetus for the search for putative loci. Both the candidate gene approach in population-based case-control studies and entire genome screening in families have helped identify susceptibility genes in a number of autoimmune diseases. 2. After the first genome screen in type 1 (insulin-dependent) diabetes mellitus it seems likely that most autoimmune diseases are polygenic with no single gene being either necessary or sufficient for disease development. Of the organ-specific autoimmune diseases, genome screens have now been completed in insulin-dependent diabetes mellitus and multiple sclerosis. Furthermore, the clustering of autoimmune diseases within the same individuals suggests that the same genes may be involved in the different diseases. This is supported by data showing that both HLA (human leucocyte antigen) and CTLA-4 (cytotoxic T-lymphocyte-associated-4) appear to be involved in the development of insulin-dependent diabetes mellitus and Graves' disease. 3. Genome screens have also been completed in some of the non-organ-specific autoimmune diseases including rheumatoid arthritis, inflammatory bowel disease and psoriasis. Many candidate genes have also been investigated although these are predominantly in population-based case-control studies. 4. Substantial progress has been made in recent years towards the identification of susceptibility loci in autoimmune diseases. The inconsistencies seen between case-control studies may largely be due to genetic mismatching between cases and controls in small datasets. Family-based association studies are being increasingly used to confirm genetic linkages and help with fine mapping strategies. It will, however, require a combination of biology and genetics, as has been necessary with the major histocompatibility complex in insulin-dependent diabetes mellitus, to identify primary aetiological mutations.

The point accuracy of paediatric population registers

The accurate identification of paediatric populations in primary health care is not being achieved. Fifteen per cent of the children were not at the address given for them on one or more of the three registers studied. Our calculations suggest that a further number of children in the community may appear on none of the three available registers.