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Here is an old post to the Celiac Listserv in response to Lissy's Sat, 24
Apr 1999 17:42:17 -0700 post. It was originally prepared by Bill Elkus and
I am re-posting it:

Date: Fri, 14 Apr 1995 04:57:27 GMT
From: William Elkus <[log in to unmask]>
Subject: Genetic Testing

Several people have asked about genetic testing for Celiac Disease. I am
not a medical professional, but I have learned a little about this topic
from my contacts, and from reading the excellent medical textbook 'Coeliac
Disease' edited by Michael Marsh and published in 1992 by Blackwell
Scientific (ISBN 0-632-03097-6). This book covers many Celiac subjects in
great deal. Its main disadvantage is its price (over $200) but some medical
libraries carry it.

My understanding is that about 25% of the population in the US and Western
Europe has the genetic HLA markers which are associated with Celiac
Disease. The current state of the art of genetic testing cannot predict
which of those within the 25% will get CD, so this test is of greatest
value to those in the 'other' 75% for which CD can essentially be ruled out.
The HLA markers for CD are the same markers associated with juvenile
diabetes. My brother has diabetes, and my son has CD, so it was not
surprising when I was tested to find that I am a carrier of this HLA marker.
When one speaks about HLA markers, it is not the same as speaking about
genes. HLA testing is cruder. An analogy one doctor gave me was that gene
testing is like looking for a spelling mistake in one word of an
encyclopedia, whereas HLA testing is like finding the page with the
spelling mistake somewhere on it.

HLA terminology is very complex. To make matters worse, the geneticists
have changed the coding they use. DR3 is the most common term used to
describe the particular HLA marker most often seen in CD. That same marker
is now called DRw17. Either way, this marker is usually seen in concert
with other HLA markers which are together termed an 'extended haplotype'.
Most people do not have extended haplotypes. Those that do have a greater
tendency to come down with autoimmune disorders than the rest of the
population. The B8-SC01-DR3-DQ2 extended haplotype (note the DR3 inside) is
the most common in the US population, and the great majority of Celiacs
have at least one or their two chromosomes with this extended haplotype.
According to Dr. Martin Kagnoff (who wrote the chapter on genetics in the
Marsh book), essentially all Celiacs have two particular _subfactors_ of
HLA markers. If a person has just one copy of the gene which codes for DR3,
they automatically get both the subfactors and become part of the HLA risk
group. There is another way to get these two subfactors, and that is to
have DR5 on one chromosome and DR7 on the other. These people are called
DR5/7 heterozygotes, but these people are a minority of CD cases.

I had an opportunity to meet Dr. Kagnoff, and asked him what happens if a
person has both chromosomes with DR3 instead of just one. His reply was
that this has not been completely researched, but it appears that it
results in a somewhat more severe case of Celiac.

Kagnoff and others suspect that there are additional genes involved in CD,
and research continues. It is possible that more predictive markers will be
discovered in the future. Since HLA typing is expensive ($350 to $550 in
Los Angeles), and not very predictive, it is hard to justify. If you are
part of a family with two siblings with CD, free HLA typing may be
available through a research project in Utah. Do a search of the archives
on "Utah and gene' to find the announcement.

Bill Elkus

Scott Adams - San Francisco, USA
Celiac Support Page:
http://www.celiac.com/
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