Paediatric Gastroenterologist Dr Kunal Thacker will be presenting at the Coeliac Awareness Week information session at the North Shore Private Hospital on Wednesday, 18 March 2020.
Dr Thacker has written the following article to help readers better understand how genetic testing relates to coeliac disease and the diagnostic process.
Coeliac disease (CD) is an immune disorder triggered by dietary gluten in people who carry HLA DQ2 and/or HLA DQ8 genes. These genes predispose carriers to developing an abnormal immune response to eating gluten that causes damage to the small bowel (intestine) along with varying degrees of a wide range of symptoms and associated conditions.
The risk of CD in family members of someone with CD is 10%. Because of this link, it is recommended that these family members are screened for CD. HLA testing may be helpful in this situation (Refer to the Family Screening letter available for download from www.coeliac.org.au/family-screening). In infants and young children, genetic testing does not always require a needle (a buccal/cheek swab can be taken).
But genetic screening has limitations. Approximately 50% of the general population in Australia carry at least one of these genes. Of the general public who have no other risk factors for CD and who carry the gene, only 3% develop CD over their lifetime. Thus, for most people who carry the gene the risk of developing coeliac disease is very low.
The HLA DQ2 gene is identified in 90-95% of those who are diagnosed with CD and the rest carry HLA DQ8 gene. It is very rare (<1%) that these genes are not identified in those diagnosed with CD. Hence, absence of these genes has a good negative predictive value, i.e. effectively rules out CD as an underlying diagnosis.
Genetic screening does not in itself diagnose CD, but can be useful in the following situations:
- When coeliac serology and/or small bowel examination is inconclusive or unclear
- When there has been failure to improve on a gluten free diet
- When a person has commenced a gluten free diet prior to assessment by serology or small bowel examination and are unwilling or unable to undertake an oral gluten challenge prior to investigation
- In patients clinically assessed to be at higher-risk of coeliac disease, in order to exclude those where further testing for coeliac disease is not required.
You may find the additional information about diagnosis on web page www.coeliac.org.au/diagnosis helpful, particularly the fact sheet available for download – Testing and diagnosis of coeliac disease in children.
Members of Coeliac Australia’s MAC have developed an evidence-based approach to guide clinically appropriate use of HLA typing (genetic screening) onlinelibrary.wiley.com/doi/10.1111/imj.12716/abstract
Dr Kunal Thacker works as a paediatric gastroenterologist and hepatologist at The Children’s Hospital at Westmead (CHW), Sydney. At CHW he is involved in regular educational and research activities with a focus on Inflammatory Bowel Disease and Eosinophilic Oesophagitis.