A research paper this past summer tried to link some of the diseases that affect humans (at least the ones we have a genetic link of some sort) into a giant human "diseaseome." Like the genome, the diseaseome is a map, a network if you will, connecting different diseases to one another by way of their genetics. Click the above link for an interactive graphic. The majority of the results weren't that surprising. Most cancers clustered together. So did a lot of other organ-system-specific diseases.
The really interesting ones, however, were those that didn't cluster where you might expect.
I went spelunking through the graphic for eating disorders, or, at the least, psychiatric illnesses. I found them, in the corner. And I found anorexia, linked to seasonal affective disorder, alcohol dependence, and OCD by way of the 5-HT2A receptor gene (see below for a close-up of this section).
5-HT2A is a serotonin receptor, and binding of serotonin to this receptor causes a neuron to fire. The gene that codes for this receptor (HRT2A) has a variety of polymorphisms (i.e., slight variations) that have been linked to psychiatric illnesses, such as major depression, bipolar disorder, OCD and traits like neuroticism.
And anorexia fits neatly within these variations.
The little circle representing anorexia sits happily among other psychiatric illnesses. But what really stood out for me was the color of the circle. Different colors symbolize different diseases. Anorexia was not colored a dark magenta like the other brain diseases; AN had an orange circle. Looking on the key, I see that anorexia is classicied as a nutritional disease.
A poster that got it right, with one little dot and one little color. A nutritional disease linked to serotonin malfunctions and other psychiatric illnesses.