I spend a lot of time thinking about childhood anorexia nervosa and have both written and lectured on my belief that anorexia is a highly heritable brain disorder initiated by some environmental trigger, e.g. diet, stress, virus, strep infection, etc.
This explanation made the most sense to me until I recently read a short but very dense article by Thomas Insel and Phillip Wang of the NIMH, published in JAMA (May 19, vol. 303 No 9). This little article was so dense I had to read it four times in order to really understand it.
The paper discusses the fact that, although there is now an avalanche of information about the genetics of brain disorders such as schizophrenia, autism, ADHD and others, only a fraction of the heritability confirmed in twin studies and by family genograms (aka family “tree”) seems to be explained by variations in the genes studied to date. So-called copy number variants have been found in some families with these illnesses; disappointingly, they do not map onto specific illnesses as we know them or define them. In fact, the authors point out that “within families, the same copy number variant may be associated with schizophrenia in one person, bipolar disorder in another, and attention deficit/hyperactivity disorder in yet another.”
The authors go on to say, “the genetics of mental illness may really be the genetics of brain development, with different outcomes possible, depending on the biological and environmental context.” They postulate that what we see as a cluster of symptoms (which we then call “schizophrenia” or “ADHD”) may appear to us to have cropped up at the age we first notice them, but actually be neuro-developmental in nature, that is, later stages in biological processes that started much earlier in development. In other words, when we see the illness, it has already been present in sub-threshold form for years.
Oh wow.
What about anorexia nervosa? What if something went wrong in earliest development (within the womb?), which then set in motion a virtually inevitable disease process? In some people such a brain disorder might surface recognizably as early as age 6 or 7, in others it would be recognized later in childhood or adolescence and in some few people only in adulthood. If you did not know that a person harbored a neuro-developmental disorder, you would be tempted to think that the time when symptoms first became apparent to you was the time when the disease “started” or was “triggered,” when in fact the disorder had existed far longer, slumbering along in a form you were not able to detect.
In other words, what if there is no trigger?
Insel and Wang conclude their paper by holding out the hope that very early (genetic?) recognition of a person’s vulnerability could eventually lead to meaningful early intervention, including prevention.
Stay tuned. Oh, and do please read the article for yourselves. An accessible summary of it can be found here.
