Ok, so it has taken 3 or 4 days to get this straight and I might not even have it right, but I think I do. So, let’s get going.
There are two commonly associated genes with Celiac – HLA-DQ2 and HLA- DQ8. These can be further broken down into specific alleles or pairs on the gene. Each of these encode for specific reactions. Over 80% of those with celiac disease have HLA-DQ2 so it is more studied than DQ8. I’m going to talk more about DQ2 because that is what I have.
So, there are two parts to the HLA-DQ2.5 portion of the genetics. There is an alpha and beta portion. There are two ways that you can get DQ2.5 either DQA1*0501:DQB1*0201 or DQA1*0501:DQB1*0202. Both of those encode for HLA-DQ2.5. Don’t forget there is also HLA-DQ2.2 ( DQA1*0201:DQB1*0202), HLA-DQ2.3 ( DQA1*0303:DQB1*0202) , and HLA-DQ8. DQ2.2 is also known as 2.5 in trans form. Note, that the number is related to the alpha portion – 2.5=*0205, 2.3=*0303, 2.2=0201.
It seems that the HLA-DQ2.5 variation is also highly associated with a variety of other autoimmune diseases. Celiac is not the only autoimmune disease associated with DQ2.5 – dermatitis herpetiformis, juvenile diabetes, Sjogren’s syndrome, and autoimmune hepatitis as related to celiac. So, when they say, celiac is often associated with other autoimmune diseases – this is why! I really never knew why they said this and thought it might be hooey, but it isn’t.
The 23 and Me genetic test only reports the alpha portion of the DQ2 gene. This threw me off. The beta portion of the allele tells whether the gene is in cis or trans form. Cis or trans form and that factors a bit into all of this but it is really hard for me to understand because that gets into the real nitty gritty.
So, hopefully this gives some information on the genetics of celiac. Sorry it took so long.