Molecular analysis of HLA-DQ A alleles in coeliac disease lack of a unique disease-associated sequence

T-cell receptor variable genes and genetic susceptibility to celiac disease: an association and linkage study

BACKGROUND

Genetic susceptibility of celiac disease is primarily associated with a particular combination of and HLA-DQA1/DQB1 gene; however, this does not fully account for the genetic predisposition. Therefore, the aim of this study was to examine whether T-cell receptor (TCR) genes may be susceptibility genes in celiac disease.

METHODS

HLA class II typing was performed by polymerase chain reaction amplification in combination with sequence-specific oligonucleotide hybridization. TCR alpha (TCRA), TCR gamma (TCRG), and TCR beta (TCRB) loci were investigated by restriction fragment length polymorphism analysis.

RESULTS

Allelic frequencies of TCRA, TCRG, and TCRB variable genes were compared between patients with celiac disease (n = 53) and control patients (n = 67), and relative risk (RR) estimates were calculated. The RR was 1.67 for allele C1 at TCRA1, 3.35 for allele D2 at TCRA2, 1.66 for allele B2 at TCRG, and 1.35 for allele B at TCRB, showing no significant association. Additionally, linkage analysis was performed in 23 families. The logarithm of odd scores for celiac disease vs. the TCR variable genes at TCRA, TCRG, and TCRB showed no significant linkage.

CONCLUSIONS

These data suggest that the analyzed TCR variable gene segments V alpha 1.2, V gamma 11, and V beta 8 do not play a major role in susceptibility to celiac disease.

Asp57-negative HLA DQ beta chain and DQA1*0501 allele are essential for the onset of DQw2-positive and DQw2-negative coeliac disease

The genetic predisposition to coeliac disease is associated with the HLA DQw2 allele. Coeliac patients lacking the DQw2 allele are very rare and always exhibit the DR4-DQw3 haplotype. We performed oligotyping of polymerase chain reaction (PCR)-amplified DQA1 and DQB1 genes in six DQw2-negative and 30 DQw2-positive coeliac patients. The DQB analysis showed that all six DQw2-negative patients possessed the DQB1*0302 allele. The other DQB alleles found in five of these patients were DQB1*0501, DQB1*0604 and DQB1*0302. The DQ beta chains encoded from all these alleles have the replacement of aspartic acid residue at position 57 (Asp57), as well as the DQB1*0201 allele which was found in all 30 DQw2-positive coeliac patients. The DQw2-negative proband who lacked the homozygous Asp57 replacement exhibited the DQA1*0501 allele in the DQA1 gene. The DQA1*0501 allele was also found in 27 of the 30 DQw2-positive coeliac patients. Among this group of coeliacs, the four cases lacking the DQA1*0501 allele exhibited the homozygous Asp57 replacement in the DQ beta chain. Our results indicate that Asp57-negative DQ beta alleles are involved in both DQw2-positive and -negative coeliac patients. Moreover, when the Asp57-negative DQ beta chain is encoded from only one of the two DQB1 genes the DQA1*0501 allele is always present.

HLA-DP polymorphism in northern Italian celiac patients

The contribution of HLA-DP genes to celiac disease susceptibility has been investigated in 95 Italian patients, 41 with childhood and 54 with adult disease onset. Polymerase chain reaction amplification, sequence-specific oligonucleotide probe hybridization and restriction fragment length polymorphism analyses have been carried out. All celiac patients and 56 out of 128 random healthy controls were DQw2-positive. The frequency of the DPB1*0101 allele was significantly increased (pc = 0.002, relative risk 5.21) in patients with celiac disease (23.2%) compared to the whole panel of controls (5.5%), but not to the 56 controls bearing DQw2 (10.7%). No significant difference in the frequency of DPB1*0101 was found between celiac patients with pediatric (24.4%) or adult (22.2%) onset. The DPB1*0101 allele was associated with both the DR3-DQw2 and DR7-DQw2 haplotypes. Moreover, our study has not confirmed the association with DPB1*0402 and DPB1*0301 previously reported in celiac children from southern Italy. The linkage of the DPB1*0101 allele with the DQ locus and the observation that the DP but not the DQ association appears to be ethnically dependent strongly support a secondary role of DP molecules in celiac disease susceptibility.