Estimation of diabetes risk in Brazilian population by typing for polymorphisms in HLA-DR-DQ, INS and CTLA-4 genes.

The study aimed to further characterise HLA encoded risk factors of type 1 diabetes (T1D) in Brazilian population and test the capability of a low resolution full-house DR-DQ typing method to find subjects at diabetes risk. Insulin and CTLA-4 gene polymorphisms were also analysed. The method is based on an initial DQB1 typing supplemented by DQA1 and DR4 subtyping when informative. Increased frequencies of both (DR3)-DQA1*05-DQB1*02 and DRB1*04-DQA1*03-DQB1*0302 haplotypes were detected among patients. DRB1*0401, *0402, *0404 and *0405 alleles were all common in DQB1*0302 haplotypes and associated with T1D. (DRB1*11/12/1303)-DQA1*05-DQB1*0301, (DRB1*01/10)-DQB1*0501, (DRB1*15)-DQB1*0602 and (DRB1*1301)-*0603 haplotypes were significantly decreased among patients. Genotypes with two risk haplotypes or a combination of a susceptibility associated and a neutral haplotype were found in 78 of 126 (61.9%) T1D patients compared to 8 of 75 (10.7%) control subjects (P < 0.0001). Insulin gene -2221 C/T polymorphism was also associated with diabetes risk: CC genotype was found among 83.1% of patients compared to 69.3% of healthy controls (P=0.0369, OR 1.98) but CTLA-4 gene +49 A/G polymorphism did not significantly differ between patients and controls. Despite the diversity of the Brazilian population the screening sensitivity and specificity of the used method for T1D risk was similar to that obtained in Europe.

A linkage study of 12 IDDM susceptibility loci in the Finnish population.

BACKGROUND: HLA region is the major locus (IDDM1) of type 1 diabetes (T1D) susceptibility. It explains approximately 50% of the genetic background of T1D, indicating additional genetic determinants. Genome scans and candidate gene studies have generated several chromosomal candidate regions that may have a role in T1D development. METHODS: We tested 12 of these loci for linkage in 107 Finnish T1D multiplex families using 23 microsatellite markers and 2 SNPs. Families were stratified according to the HLA status and sharing at the DQB1 gene. RESULTS: We found no significant or suggestive MLS in our unstratified families outside the IDDM1 locus. The highest MLS was seen close to the IDDM9 region marker D3S3576 at 3q21-q25 (MLS=1.05). This marker also had a global p-value of 0.0032 (ETDT) in maternal transmissions. IDDM6 and 12q12-q15 region showed MLS=1.1 and MLS=1.3 respectively in HLA-DQB1*0302/x (x is not equal to HLA-DQB1*02) stratified families. IDDM12 showed MLS=2.0 in HLA-DQB1 identical sib pairs. Linkage at IDDM12 was supported by a global p-value of 0.0006 (uncorrected) in ETDT. For IDDM2, p-values of 0.028 and 0.009 were observed in ETDT with MspI-2221 SNP in unstratified and HLA-DQB1*0302/x-stratified families respectively. CONCLUSIONS: Our results are consistent with previous findings of linkage or association to T1D at IDDM2, IDDM6, IDDM9, IDDM12 and 12q12-q15 regions but do not unambiguously confirm them. A larger sample set is required to gain statistical power needed to confirm our findings in the Finnish population.

Estimation of genetic risk for type 1 diabetes.

The most important gene loci defining risk of type 1 diabetes mellitus (T1DM) are located within the HLA gene region. HLA-DQ molecules are of primary importance but HLA-DR gene products modify the risk conferred by HLA-DQ. The risk associated with an HLA genotype is defined by the particular combination of susceptible and protective alleles. The highest risk is associated with a combination of two different risk haplotypes (7% risk to develop T1DM in Finland) whereas protective genotypes covering 69% of population have a risk of less than 0.2%). The complicated analysis of HLA genotypes is simplified by strong linkage disequilibrium between HLA-DRB1, -DQA1 and -DQB1 loci. In many cases one can deduce the alleles of other loci based on determination of the alleles in one locus. Differences between various populations in the frequency of marker alleles and in the linkages between them has to be taken into account. We have developed PCR based typing methods that utilize blood spot samples, microtiter plate format and lanthanide labeled oligonucleotide probes to define HLA-DQ and -DR alleles relevant for T1DM risk. Typing is run stepwise so that after initial HLA-DQB1 typing only those samples will be further analyzed in which -DQA1 or -DRB1 typing is informative and expected to contribute to the risk estimation. This method has been used to screen more than 50,000 newborn infants in Finland over a time period of 6 years, and it has been able to identify most children who have developed T1D during the follow-up period. The efficiency of the procedure has also been tested in Finnish and Greek populations.

Genetic risk determines the emergence of diabetes-associated autoantibodies in young children.

Timing of onset of autoimmunity is a prerequisite for unmasking triggers and pathogenesis of type 1 diabetes. We followed 4,590 consecutive newborns with 8 or 3% HLA-DQB1 conferred risk for type 1 diabetes at 3-, 6-, or 12-month intervals up to 5.5 years of age. Islet cell autoantibodies (ICAs) and, in the 137 children with ICAs, insulin autoantibodies (IAAs), GAD65 autoantibodies (GADAs), and IA-2 protein autoantibodies (IA-2As) were measured. Children with high genetic risk developed ICAs more often than those with moderate risk (log-rank P = 0.0015); 85 and 91% remained ICA negative by 5 years of age, respectively. The time of appearance of biochemical autoantibodies was then compared with the appearance of ICAs. IAAs and GADAs emerged usually before ICAs (means -1.8 and -1.5 months, respectively) and IA-2As after ICAs (mean 2.0 months). Ninety-five percent of all IAAs, GADAs, and IA-2As seroconversions occurred in a cluster (-12 to 8 months) around the ICA seroconversion. We conclude that diabetes-associated autoantibodies emerged in children with predisposing HLA-DQB1 alleles after 3 months of age at a constant tempo, determined by the genetic risk level, usually in the order of IAA, GADA, ICA, and IA-2A. Seroconversion to multiple autoantibody positivity usually occurred tightly clustered in time.

HLA class II associated risk and protection against multiple sclerosis-a Finnish family study.

We analyzed the HLA class II haplotypes in 249 Finnish nuclear families and compared the frequencies of parental haplotypes transmitted or non-transmitted to multiple sclerosis (MS) patients. The most important predisposing haplotype was DRB1*15-DQB1*0602 (P<10(-6)) as expected and a weak predisposing effect of DRB1*04-DQB1*0302 was revealed after the elimination of DRB1*15-DQB1*0602. HLA-DRB1*01-DQB1*0501 and DRB1*13-DQB1*0603 were negatively associated with MS in transmission disequilibrium test, but only the DRB1*13-DQB1*0603 association remained significant (P=0.008) after the elimination of DRB1*15-DQB1*0602 haplotypes. Based on this study HLA class II haplotypes exhibit both predisposing and protective effects in MS.