Folie à deux in Japan -- analysis of 97 cases in the Japanese literature.

In order to clarify the characteristics of folie à deux in Japan, we examined a total of 97 cases of folie à deux in the Japanese literature covering a period of 90 years, and compared them with the cases reported in Western countries. About 75% of the Japanese cases occur in two individuals, and of these are family cases. The most common combinations are mother-child and married couple. Mother-child combinations are much more common than father-child combinations. Female subjects are more often involved than males. The most common diagnosis for the dominant partner is schizophrenia, and the most common diagnosis for the submissive partner is paranoid reaction. Delusion is the most common symptom shared by both partners in Japan. Comparing these Japanese cases to Western ones, sister-sister combinations are less frequent, younger subjects influence the older ones more, and acute religious delusion is more common in Japan than in Western countries.