Genetic susceptibility to type 1 diabetes: clinical and molecular heterogeneity of IDDM1 and IDDM12 in a german population

Association of cytotoxic T lymphocyte antigen-4 gene polymorphisms and HLA class II alleles with the development of type 1 diabetes in Korean children and adolescents

We studied the association of cytotoxic T lymphocyte antigen-4 gene (CTLA4) polymorphisms with the development of type 1 diabetes (T1D) in Korean children and adolescents. A total of 176 Korean subjects (92 females and 84 males) with childhood-onset T1D were studied. The A/G polymorphism at position 49 in CTLA4 exon 1 and the C/T polymorphism at position -318 in the CTLA4 promoter were analyzed by PCR-RFLP methods. The genotype and allele frequencies of the CTLA4 polymorphisms in the T1D patients were not different from those in the controls. These polymorphisms were not associated with the clinical characteristics or the development of autoimmune thyroid disease in the T1D patients. The frequency of the A allele was significantly higher in the patients that did not have two out of the three susceptible HLA-DRB1 alleles, which were DRB1*0301, *0405 and *09012, compared to the controls (P<0.05). These results suggest that CTLA4 polymorphisms do not directly confer any susceptibility to T1D. However, a CTLA4-mediated susceptibility effect on the development of T1D might be significant in children and adolescents that do not have susceptible HLA class II alleles.

No association of CTLA4 gene with celiac disease in the Basque population

BACKGROUND

Celiac disease (CD) is an autoimmune disorder caused by intolerance to ingested gluten that develops in genetically susceptible individuals. The contribution of human leukocyte antigen (HLA) genes to the genetic risk to CD has been known for a long time; however, non-HLA genetic factors are likely to be required for the development of the disease. Several studies have associated the CD28/CTLA4 region on chromosome 2q33 with the disease in different populations. The CTLA4 gene encodes a receptor involved in the control of T-cell proliferation and mediates T-cell apoptosis. AIM To determine the contribution of two polymorphisms of the CTLA4 to the disease: the A/G dimorphism at position +49 in exon 1 and the (AT)(n) microsatellite in the 3' untranslated region.

PATIENTS

Forty-one celiac families of Basque origin (43 patients with CD and 80 first-degree relatives).

METHODS

Restriction enzyme digestion of polymerase chain reaction amplified genomic DNA for the A/G dimorphism and polymerase chain reaction followed by high-resolution electrophoresis for the (AT)(n) microsatellite. For disease association studies, the Affected Family Based Controls approach was used.

RESULTS

The frequency of the A allele of 49 A/G polymorphism was 67.47% in the celiac allele group compared with 70.13% in the Affected Family Based Controls group. These differences were not significant. Analysis of the (AT)(n) polymorphism identified 17 different alleles, ranging from 262 to 312 bp in length, but no allele was significantly associated with the disease.

CONCLUSIONS

Our results did not show any evidence of association of any of the CTLA4 gene polymorphisms with the disease. This may result from population-specific differences in genetics and environmental susceptibility to CD.

Relation of three polymorphisms of the CTLA-4 gene in patients with Graves' disease

Graves' disease is an autoimmune disease believed to be caused by a combination of environmental and genetic factors. One of the candidate genes is CTLA-4, a negative regulator of T cell activation. Three polymorphisms of the gene have been described, in the promoter at position -318, at position 49 in exon 1, and an (AT)n repeat within the 3'-untranslated region of exon 4. Many studies describe the association between a polymorphism of the CTLA-4 gene and autoimmune disease. To investigate the association of these CTLA-4 gene polymorphisms with each other, we analyzed the combined frequencies of each polymorphism and calculated the disequilibrium coefficients. We studied DNA samples from 120 Graves' disease (GD) patients and 80 healthy donors (NC). The exon 1 position 49 A/G polymorphism and promoter polymorphism at position -318, were typed using a PCR-restriction fragment length polymorphism method (PCR-RFLP). The polymorphic (AT)n repeat in exon 4 was determined by PCR amplification of genomic DNA, resolution of the amplified products on sequencing gels, and detection by autoradiography. There was a significant difference between GD and NC patients and occurrence of the polymorphism in exon 1 and exon 3, but not for the polymorphism in the promoter region. Furthermore, we found that the genotype with both the G allele in exon 1 and the 106 bp allele of the AT repeat in exon 4 occurred with much higher frequency in GD than NC (p<0.01), and that these polymorphisms are in linkage disequilibrium with each other. These results support the concept that CTLA-4 plays a critical role in the autoimmune process in GD, and that GD depends on multiple genetic susceptibility factors. Because the exon 1 and exon 4 polymorphisms are in strong linkage disequilibrium. It is not possible at this time to determine their unique relation to CTLA-4 function. Studies relating each polymorphism to CTLA4 function are required to determine whether one, or both, polymorphism(s) promote autoimmune disease.

Biological influences on obesity

Severely obese children are even more likely to have mutations in obesity genes than are severely obese adults. Thus, investigators searching for obesity genes commonly focus on children, with the result that many human obesity genes were first identified in studies of children. Although the development of obesity depends on living in an obesity-promoting environment, it also is influenced strongly by individual genetic composition. Thus, the discovery of new obesity genes provides new opportunities to identify causes of severe obesity. Finally, identification of individual causes of obesity may, in the future, provide for a safe, effective, and individualized treatment recommendation for each obese person.

CTLA4 gene polymorphisms are associated with, and linked to, insulin-dependent diabetes mellitus in a Russian population

BACKGROUND

The association between the human cytotoxic T lymphocyte-associated antigen-4 (CTLA4) gene and insulin-dependent diabetes mellitus (IDDM) is unclear in populations. We therefore investigated whether the gene conferred susceptibility to IDDM in a Russian population. We studied two polymorphic regions of the CTLA4 gene, the codon 17 dimorphism and the (AT)n microsatellite marker in the 3' untranslated region in 56 discordant sibling pairs and in 33 identical by descent (IBD) affected sibships.

RESULTS

The Alal7 allele of the CTLA4 gene was preferentially transmitted from parents to diabetic offspring (p<0.0001) as shown by the combined transmission/disequlibrium test (TDT) and sib TDT (S-TDT) analysis. A significant difference between diabetic and non-diabetic offspring was also observed for the transmission of alleles 17, 20, and 26 of the dinucleotide microsatellite. Allele 17 was transmitted significantly more frequently to affected offspring than to other children (p=0.0112) whereas alleles 20 and 26 were transmitted preferentially to non-diabetic sibs (p=0.045 and 0.00068 respectively). A nonrandom excess of the Ala17 CTLA4 molecular variant (maximum logarithm of odds score (MLS) of 3.26) and allele 17 of the dinucleotide marker (MLS=3.14) was observed in IBD-affected sibling pairs.

CONCLUSION

The CTLA4 gene is strongly associated with, and linked to IDDM in a Russian population.