Social Work Today E-Zine

Males who have a twin sister appear more likely to develop the eating disorder anorexia nervosa than other males, including those with a twin brother, according to a report in a recent issue of Archives of General Psychiatry. Marco Procopio, MD, MRCPsych, of the University of Sussex, England, and Paul Marriott, PhD, of the University of Waterloo, Canada, analyzed data from a study of Swedish twins born between 1935 and 1958. Two sets of diagnostic criteria, one broader and one more narrow, were used to determine which twins had anorexia nervosa.

Overall, female twins were more likely than male twins to develop anorexia nervosa. The one exception was among males who had a dizygotic (fraternal) twin sister. “In fact, their risk is at a level that is not statistically significantly different from that of females from such a pair,” the authors write. Among 4,478 dizygotic opposite-sex twins, 20 females and 16 males had anorexia nervosa using narrow criteria and 32 females and 27 males qualified under the broad criteria. Risk for these female twins was not significantly different from than that of other female twins. “A plausible explanation for this phenomenon is that in pregnancies bearing a female fetus, a substance is produced, probably hormonal, that increases the risk of having anorexia nervosa in adulthood,” the authors write. “Because the male half of an opposite-sex twin pair would also be exposed to this substance, it could account for the observed elevated risk in males with female twins.”

— Source: American Medical Association