We performed a family study of 39 individuals with proven manic-depressive disorder. Among the affected first-degree relatives of these probands, an overall parity of the male-female ratio was found. In addition, there were four instances of father-son transmission of affective illness involving probands of the sample.
These results suggest that any gene locus that exists on the X chromosome is not of itself a sufficient or necessary condition for the transmission of manic-depressive illness. Hence, any implication that X linkage is the primary mode of transmission in manic-depressive illness is premature.
Goetzl U, Green R, Whybrow P, Jackson R. X Linkage RevisitedA Further Family Study of Manic-Depressive Illness. Arch Gen Psychiatry. 1974;31(5):665-672. doi:10.1001/archpsyc.1974.01760170059010