So far, Dr. Breitner said, his group has contacted 6,000 men who are members of the twin pairs.

But, Dr. Bouchard reported, there were marked differences between the twin pairs in weight gain.

We therefore separately analysed six discordant twin pairs, and found no significant differences between healthy and affected twins.

Evidence supporting a genetic component to predisposition comes mainly from a large study of 15924 male twin pairs.

According to locals, the oldest known twin pair in the village was born in 1949.

Similar results have been obtained in 10 other studies of twins, including a Swedish investigation of 12,000 adult twin pairs.

These reports indicate concordance rates of over 50% for monozygotic twin pairs compared with under 10% for dizygotic twins.

MTFS was established in June 1989 using same-gendered twin pairs age 11 or 17.