There are two basic strategies used to look for important genes. One involves looking at families in which more than one member has an eating disorder and investigating which bits of which chromosome seem to be present in these particular members. This is called linkage. If you have enough families with enough cases in them, you can get a lead on which chromosome or bit of chromosome seems to occur consistently, and these might be concluded to be linked to Anorexia Nervosa. The problem is that those bits of chromosome contain many genes and so a great deal of work remains in trying to pin-point the precise biological factors leading to the susceptibility to the illness in question.

The other strategy is to decide what gene may be involved based on one's knowledge of the biology of the illness. You then investigate whether people with anorexia nervosa have more of an unusual form of this gene compared with the rest of the population. This is called an association study. The problem is that we do not have a complete view of all the biological pathways and networks and so it can be a bit like looking for a needle in a haystack. Both of these strategies have been used to examine genes in eating disorders.

LINKAGE

Recent research showed that an area on chromosome I was more often inherited in the people with anorexia nervosa in families which had more than one case of restricting anorexia nervosa. When all forms of anorexia nervosa were examined together this effect disappeared. This suggests that not all eating disorders are exactly the same. Some may be associated with specific genes in particular pathways, but the overall effect in terms of what we see as anorexia nervosa is rather similar. We are not sure how many types there are and how we can differentiate between them.

This is a preliminary study involving large numbers of tests in which positive results can come about by chance. These findings need to be replicated in other samples and we are hoping to do this in a European study.

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