The genetic susceptibility to Graves' disease and type 1 (insulin-dependent) diabetes mellitus is conferred by genes in the human leukocyte antigen region on the short arm of chromosome 6, but several other genes are presumed to determine disease susceptibility. Among those candidate genes is the cytotoxic T lymphocyte antigen 4 (CTLA4) located on chromosome 2q33 in man. We investigated the distribution of the CTLA4 exon 1 polymorphism (49 A/G) in Graves' disease and IDDM. This dimorphism at codon 17 results in an amino acid exchange (Thr/Ala) in the leader peptide of the expressed protein and was analyzed by PCR, single strand conformation polymorphism, and restriction fragment length polymorphism analysis in 305 patients with Graves' disease, 293 patients with IDDM, and 325 controls. Patients with Graves' disease had significantly more Ala alleles than controls, both as homozygotes (21% vs. 13%) and as heterozygotes (53% vs. 46%), and less Thr as homozygotes (26% vs. 42%; P < 2 x 10(-4). The phenotypic frequency of Ala-positive patients (73%) was significantly higher than of controls (58%; P = 10(-4); relative risk = 2). Patients with IDDM also had significantly more Ala alleles as homozygotes (19%) or heterozygotes (50%; P = 0.01). In conclusion, an alanine at codon 17 of CTLA4 is associated with genetic susceptibility to Graves' disease as well as to IDDM.

inhibits lymphocyte activation and affects other elements of the immune system, such as cytokine and immunoglobulin production, as well as major histocompatibility complex (MHC) class II and cluster of differentiation (CD)-4 expression (1). In NOD mice, the development of diabetes can be prevented by administration of 1,25(OH) 2 D 3 ( 2 ) , which inhibits lymphocyte activation and restores the altered ratio of CD4/CD8 cells.Vitamin D exerts its genomic action via the nuclear vitamin D receptor (VDR), which shows an extensive polymorphism. The VDR belongs to the steroid receptor super-family and is widely expressed in many cell types, including lymphocytes, macrophages, and pancreatic -cells (3). Four major polymorphic sites have been described within the VDR gene. A polymorphic F o kI site in exon 2 results in an alternative transcription initiation site, leading to a protein variant with three additional amino acids at the amino terminus (4). Polymorphic B s mI and A p aI sites are present in intron 8, and a silent T to C substitution creates a Ta qI restriction site in exon 9. R e c e n t l y, an association of VDR alleles with type 1 diabetes in Indian Asians has been reported (5). We therefore examined the VDR locus on chromosome 12q12-14 as a candidate gene for type 1 diabetes susceptibility in German families using extended transmission disequilibrium testing (ETDT).P a i r-wise transmission distortion testing revealed a strong linkage disequilibrium between "B" and "A" (0.1514 ± 0.0145), between "B" and "T" (-0.1953 ± 0.0148), and between "A" and "T" (-0.1322 ± 0.0144). No significant linkage disequilibrium between F o kI and any of the other sites was detectable. The allele combinations "b aT " (35.3%), "B A t" (29.5%), and "b AT " (16.8%) were most frequent in the analyzed population ( Ta b l e 1 ) .Based on the linkage disequilibrium data, ETDT analysis of the 3 -haplotypes (B s mI /A p aI /Ta qI) showed a signific a n t transmission distortion ( 2 = 18.886, df = 7, P = 0.0086). These observations (Ta b l e 2) were confirmed when looking at the two-locus haplotypes that are part of the B s mI /A p aI /Ta qI

The genetic susceptibility to rheumatoid arthritis is conferred by genes in the human leukocyte antigen (HLA) region on chromosome 6, but additional genes may be involved to determine disease susceptibility. We have studied the distribution of the CTLA4 exon 1 polymorphism (49 A/G) in rheumatoid arthritis. This dimorphism at codon 17 results in an amino acid exchange (Thr/Ala) in the leader peptide of the expressed protein and was analyzed by PCR, SSCP and RFLP in 258 Caucasian rheumatoid arthritis patients and 456 controls. Rheumatoid arthritis patients were characterized by a decreased frequency of homozygotes for the Thr-17 substitution (32% versus 39%) and an overrepresentation of patients heterozygous for the Thr/Ala substitution (54% versus 46%). Gene frequencies for the Ala/Thr substitution differed only marginally from controls. In contrast, analyses of the CTLA4 exon 1 polymorphism with respect to HLA-DRB1*04 revealed significantly more patients with Ala in the homozygous (19% versus 15% controls) or heterozygous state (54% versus 39% controls) and less homozygous for Thr (27% versus 46% controls), with a particular increase of Ala/Ala genotypes among rheumatoid arthritis patients carrying the HLA-DRB1*0401 subtype. Among HLA-DRB1*04 negative rheumatoid arthritis patients, we observed no difference between the allele frequencies of the Ala-17 or Thr-17 substitution.

Graves' disease (GD) and Hashimoto's thyroiditis (HT) are T-cell mediated organ-specific autoimmune disorders with a genetic predisposition. The cytotoxic T-lymphocyte antigen 4 (CTLA-4) molecule is the predominant receptor for B7 on activated T cells and represents a negative regulator for T-cell function. Since the CTLA-4-guanine at position 49 of exon 1 is associated with susceptibility to GD as well as to HT and IDDM, we investigated a recently detected cytosine/thymine substitution at position -318 within the CTLA-4 promoter region in patients with GD and HT. 125 patients with GD were significantly more often homozygous for cytosine (86% vs. 73% in controls, P=0.006) and less frequently heterozygous for cytosine and thymine (14% vs. 27%, P=0.008). In 64 patients with HT, the distribution was similar but not significant (81% homozygous for cytosine and 16% heterozygous). When correlating the promoter and the exon 1 polymorphism we found the strongest linkage between thymine (promoter) and adenine (exon 1). In conclusion, a promoter variant of the CTLA-4 gene represents an additional risk marker for GD and HT, but their predisposition is linked to the exon 1 alleles.