A monozygotic twin pair discordant for anorexia nervosa.

This case study describes a female monozygotic twinship in which one of the twins presented with anorexia nervosa. The case supports the suggestion from the few such discordant pairs previously reported that the affected twin tends to have been relatively disadvantaged from an early age and to be the less dominant of the pair. A review of previously reported cases suggests a concordance rate for anorexia nervosa of about 50% in female MZ twin pairs. Some methodological problems associated with the derivation of such estimates are noted.