Genetic factors in obsessive-compulsive neurosis? A rare case of discordant monozygotic twins.

There has been considerable interest in the strength of genetic predisposition to obsessive-compulsive neurosis in spite of the tendency in North America to view this disorder as entirely psychogenic. Both American and British papers have remarked on the rarity of the coincidence of obsessive-compulsive neurosis and the occurrence of MZ twins. An analysis of published reports indicates that, of those cases for which both zygosity and diagnosis can be firmly established, ten are concordant and only four discordant. Errors in previous studies that disqualify them from serious consideration include: failure of the investigators to establish zygosity with some degree of certainty; failure to distinguish between obsessive-compulsive neurosis and a mixed neurosis; and a tendency to confuse obsessive-compulsive neurosis with obsessive-compulsive personality or "obsessive traits". MZ female twins discordant for obsessive-compulsive neurosis are presented and their life histories are discussed. Although the twins were very similar in early childhood, their personality characteristics diverged remarkably, beginning at age 11, with the result that the symptomatic twin became shy, sensitive, cautious, conservative, and religious; whereas her asymptomatic sister became outgoing, confident, and adventuresome. The findings on psychiatric examination and on detailed psychological testing indicate that the obsessive-compulsive neurosis in the affected twin was clearly a phychogenic disorder.