Myofascial pain dysfunction (MPD) syndrome in twins.

The Myofascial Pain Dysfunction Syndrome (MPD) was investigated in 94 twin pairs (21 male pairs and 73 female pairs), who had not been selected with respect to MPD. The frequency of past and/or present symptoms was found to be 10% in males and 27% in females. No differences between monozygous (identical) and dizygous (non-identical) female twins was found in pair-wise concordance rates, the concordance rate being higher than expected to occur by chance in both twin types. The findings are compatible with the view that environmental influences give rise to this specific stress-reaction pattern.