What Are the HLA Genes?
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| TEST | TESTING TIME | PRICE |
|---|---|---|
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Increased Risk of Developing Celiac Disease
Identification of mutations associated with an increased risk of developing Celiac Disease allowed the development of a genetic test to assist with diagnosis. The presence of one or more specific celiac disease-associated alleles in the HLA-DQA1 and HLA-DQB1 genes (HLA-DQA1*05, HLA-DQB1*02 and HLA-DQB1*0302) can be detected in close to 100% of Celiac Disease patients. The presence or absence of celiac disease-associated alleles HLA-DQA1*05, HLA-DQB1*02 and HLA-DQB1*0302 can be determined through DNA testing.
The presence of celiac disease-associated HLA alleles implies an increased risk for celiac disease, but is not diagnostic of celiac disease as only a subset of individuals with these alleles will develop celiac disease. However, individuals who test negative for the celiac disease-associated alleles HLA-DQA1*05, HLA-DQB1*02 and HLA-DQB1*0302 can essentially exclude a diagnosis of celiac disease and have almost no lifetime risk of developing celiac disease (less than 0.04% chance), regardless of whether or not they ingest gluten.
The HLA System
The HLA genes refer to the human leukocyte antigen system, a major histocompatibility complex (MHC) in humans. The HLA genes consist of a large number of genes related to immune system function. Of particular relevance to Celiac Disease is HLA-DQ, a MHC class II type heterodimer composed of two chains, an alpha chain and a beta chain. These proteins are receptors found on the surface of cells that function to present antigens outside of the cell to T-lymphocytes. These antigens stimulate the multiplication of T-helper cells that subsequently stimulate B-cells to produce antibodies to that specific antigen. Normally, HLA-DQ is also involved in the recognition of self-antigens and presentation of these self-antigens to the immune system to develop self-tolerance at a young age. Celiac disease arises when mutations in HLA-DQ enable the resulting receptors to bind dietary gluten proteins and present them as antigens to the immune system, resulting in an immune reaction to dietary gluten.
About the HLA Genes
The HLA gene complex is a large region of approximately 3 million nucleotides located on chromosome 6. Many genes are located within this region. Of relevance to Celiac Disease are two genes, HLA-DQA1 and HLA-DQB1, located adjacent to each other at chromosome position 6p21.3. Mutations found in both of these genes are associated with an increased risk of developing Celiac Disease. Several celiac disease-associated alleles have been identified for these two genes: HLA-DQA1*05, HLA-DQB1*02 and HLA-DQB1*0302.
Facts About the HLA-DQ Genes
| Name of gene | HLA-DQ |
| Other names for the gene | HLA class II antigen CELIAC1 |
| Mode of inheritance | Autosomal recessive or autosomal dominant, depending on the mutation |
| Chromosomal location | 6p21.3 |
| Function of this gene product | Recognizes and presents foreign antigens to T-cells and is involved in recognition of self-antigens |
| Diseases associated with defects in this gene | Major cause of Celiac Disease Involved in diabetes mellitus type 1 |
| Mutations which cause defects in this gene that are associated with Celiac Disease |
HLA-DQA1*05
HLA-DQB1*02 HLA-DQB1*0302 |
