SOME cases of anorexia may be caused by a gene mutation. If this finding is confirmed, it could lead to better treatments not only for anorexia but also for other psychiatric disorders.
No one knows why some people 鈥� mostly young women 鈥� become obsessed with weight loss, sometimes starving themselves to death. The disease has been blamed on everything from not wanting to grow up to the Western obsession with skinny women. However, there is evidence that the disease occurs in other cultures and also runs in families, which suggests there is a genetic element.
To find out, Ruth Urwin and Ken Nunn at the Children鈥檚 Hospital at Westmead, Sydney, studied 87 young anorexic women and their parents. They found that anorexic women who control their weight by starving themselves, rather than by vomiting, are twice as likely to have a mutated version of a gene called NET as non-anorexics (Molecular Psychiatry, vol 7, p652).
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The gene鈥檚 protein product, called the norepinephrine transporter, controls the uptake of a neurotransmitter called norepinephrine by nerve endings in the brain. Norepinephrine is implicated in stress and anxiety.
鈥淚t鈥檚 one of the first hints of a gene that may be involved in anorexia nervosa. It鈥檚 really fascinating,鈥� says Philip Mitchell, head of psychiatry at the University of New South Wales. But claims that genes are linked to psychiatric disorders haven鈥檛 always stood up to scrutiny, he warns, so it鈥檚 vital that the finding is confirmed.
If it is, it could explain why attempts to treat anorexic patients with antidepressants have had little success, even though many are also depressed. These efforts have usually involved drugs such as Prozac that alter the uptake of another neurotransmitter, serotonin. 鈥淚t could be the wrong transmitter system,鈥� says Nunn. 鈥淲e鈥檙e now going to look at norepinephrine drugs to see if they are any more effective in anorexia.鈥�
Better treatments are needed desperately. At the moment therapy tends to involve dietary supervision and behavioural therapy, but the death rate among anorexics is still one of the highest for any psychiatric disorder.
Urwin and Nunn also plan to investigate how the mutation affects the activity of NET鈥檚 protein. The mutation is in the gene鈥檚 promoter region 鈥� the 鈥渟witch鈥� that controls its activity. Previous attempts to sequence the gene had missed well over a third of the promoter region. 鈥淚t鈥檚 a very unstable region. That鈥檚 why they missed it,鈥� says Urwin.
It could also explain why no one has found a link between mutations in NET and a major mental disorder before, despite the fact that several psychiatric drugs affect the protein鈥檚 activity. NET may play a role in other illnesses, too.