Sex differences in concordance rates for schizophrenia in twins.

In response to my discussion of sex differences in concordance rates for schizophrenia in twins, Lewine (1979) noted that male schizophrenics are hospitalized earlier than females. He questioned whether females had been followed through the risk period. To clarify, I calculated the age at followup of discordant twins in three studies. In Gottesman and Shields' (1972) study, the majority of both male and female co-twins were still under the age of 45. In contrast, all but a few of Kringlen's (1967a, 1967b, 1968) and Fischer's (1973) co-twins were 45 or over. Their findings support the conclusion that recent twin studies show no significant sex differences in concordance.