A pedigree-based linkage study of coeliac disease: failure to replicate previous positive findings

Prevalence of celiac disease among relatives of sib pairs with celiac disease in U.S. families

OBJECTIVE

Celiac disease is a familial malabsorptive disorder with an estimated prevalence in first-degree relatives of 10-12%. The prevalence for first-degree and more distant relatives has not been determined in families where there are two affected first-degree relatives. The aim of our investigation was to estimate the prevalence and relative risk for celiac disease in relatives of two siblings diagnosed with celiac disease.

METHODS

We ascertained sib pairs with celiac disease, and then identified all living first-degree relatives and available second-degree relatives to minimize ascertainment bias. We measured IgA endomysial antibodies, a highly specific and sensitive assay for celiac disease, in all subjects without a confirmed biopsy diagnosis. For those individuals with positive serologic tests, IgA tissue transglutaminase antibody tests and human leukocyte antigen DQA1 and DQB1 genotyping were performed for additional confirmation. Individuals with positive biopsy and/or serology were considered affected. We calculated the relative risk of being affected with celiac disease using the lambda(R) statistic.

RESULTS

The prevalence of celiac disease in relatives of affected sib pairs was as follows: 21.3% (13/61) of siblings (lambda(S) = 53); 14.7% (10/68) of offspring (lambda(O) = 37); 17.2% (28/163) of first-degree relatives; 19.5% (16/82) of second-degree relatives; and 17.8% (52/292) of all relatives (lambda(R) = 44.5).

CONCLUSIONS

In these families, we identified a sibling risk approximately double that found in previous reports, as well as significant risk for more distant relatives, probably because of sharing of a common gene. In families where at least two siblings have been diagnosed with celiac disease, relatives are at high risk for celiac disease. Screening should be considered for all family members.

Genomewide linkage analysis of celiac disease in Finnish families

Celiac disease (CD), or gluten-sensitive enteropathy, is a common multifactorial disorder resulting from intolerance to cereal prolamins. The only established genetic susceptibility factor is HLA-DQ, which appears to explain only part of the overall genetic risk. We performed a genomewide scan of CD in 60 Finnish families. In addition to strong evidence for linkage to the HLA region at 6p21.3 (Z(max)>5), suggestive evidence for linkage was found for six other chromosomal regions--1p36, 4p15, 5q31, 7q21, 9p21-23, and 16q12. We further analyzed the three most convincing regions--4p15, 5q31, and 7q21--by evaluation of dense marker arrays across each region and by analysis of an additional 38 families. Although multipoint analysis with dense markers provided supportive evidence (multipoint LOD scores 3.25 at 4p15, 1.49 at 5q31, and 1.04 at 7q21) for the initial findings, the additional 38 families did not strengthen evidence for linkage. The role that HLA-DQ plays was studied in more detail by analysis of DQB1 alleles in all 98 families. All but one patient carried one or two HLA-DQ risk alleles, and 65% of HLA-DQ2 carriers were affected. Our study indicates that the HLA region harbors a predominant CD-susceptibility locus in these Finnish families.

The tissue transglutaminase gene is not a primary factor predisposing to celiac disease

OBJECTIVES

The aim of this study was to determine whether the tissue transglutaminase (tTG) gene is a causal factor in the pathogenesis of celiac disease (CD).

METHODS

A total of 147 Dutch families with at least one patient with biopsy-proven CD were available for this study. In all patients, CD was diagnosed according to the revised European Society for Pediatric Gastroenterology and Nutrition criteria. A microsatellite marker in a noncoding region of the tTG gene was investigated for both linkage and association. Linkage was tested by determining the amount of allele sharing between affected brothers and sisters (affected sibling [sib] pair analysis). Association was determined by comparing transmission of certain tTG alleles from parents to CD patients to the nontransmitted alleles by the transmission/disequilibrium test.

RESULTS

Linkage analysis did not show cosegregation of the tTG gene with celiac disease in our families, and there was no association between certain tTG alleles and celiac disease. Furthermore, the tTG gene could be excluded as a CD susceptibility gene.

CONCLUSION

Our results indicate that the tTG gene can be excluded as a major primary genetic factor in CD pathogenesis.

Linkage analysis of HLA and candidate genes for celiac disease in a North American family-based study

BACKGROUND

Celiac disease has a strong genetic association with HLA. However, this association only explains approximately half of the sibling risk for celiac disease. Therefore, other genes must be involved in susceptibility to celiac disease. We tested for linkage to genes or loci that could play a role in pathogenesis of celiac disease.

METHODS

DNA samples, from members of 62 families with a minimum of two cases of celiac disease, were genotyped at HLA and at 13 candidate gene regions, including CD4, CTLA4, four T-cell receptor regions, and 7 insulin-dependent diabetes regions. Two-point and multipoint heterogeneity LOD (HLOD) scores were examined.

RESULTS

The highest two-point and multipoint HLOD scores were obtained in the HLA region, with a two-point HLOD of 3.1 and a multipoint HLOD of 5.0. For the candidate genes, we found no evidence for linkage.

CONCLUSIONS

Our significant evidence of linkage to HLA replicates the known linkage and association of HLA with CD. In our families, likely candidate genes did not explain the susceptibility to celiac disease.

The CTLA4/CD28 gene region on chromosome 2q33 confers susceptibility to celiac disease in a way possibly distinct from that of type 1 diabetes and other chronic inflammatory disorders

The effect of the gene region on chromosome 2q33 containing the CD28 and the cytotoxic T-lymphocyte associated (CTLA4) genes has been investigated in several diseases with chronic inflammatory nature. In addition to celiac disease (CD), type I diabetes, Grave's disease, rheumatoid arthritis and multiple sclerosis have all demonstrated associations to the A/G single nucleotide polymorphism (SNP) in exon 1, position +49 of the CTLA4 gene. The purpose of this study was to investigate this gene region in a genetically homogeneous population consisting of 107 Swedish and Norwegian families with CD using genetic association and linkage methods. We found a significant association with preferential transmission of the A-allele of the exon 1 +49 polymorphism by using the transmission disequilibrium test (TDT). Suggestive linkage of this region to CD was moreover demonstrated by non-parametric linkage (NPL) analysis giving a NPL-score of 2.1. These data strongly indicates that the CTLA4 region is a susceptibility region in CD. Interestingly, of the several chronic inflammatory diseases that exhibit associations to the CTLA4 +49 A/G dimorphism, CD appears to be the only disease associated to the A allele. This suggests that the +49 alleles of the CTLA4 gene are in linkage disequilibrium with two distinct disease predisposing alleles with separate effects. The peculiar association found in the gut disorder CD may possibly relate to the fact that the gastrointestinal immune system, in contrast to the rest of the immune system, aims to establish tolerance to foreign proteins.