Sex chromosome mosaicism in disorders of sexual differentiation: Incidence in various tissues**

Some patients with sexual anomalies have sex chromosome mosaicism. It often is stated that unless cells from multiple tissues are cultured and karyotyped, many cases of sex chromosome mosaicism will be overlooked. In the present study, involving 31 cases of Turner's syndrome, 8 cases of male pseudohermaphroditism, and 4 cases of Klinefelter's syndrome, an effort was made to obtain cells from other tissues, as well as from peripheral blood for culture and karyotyping. In only one instance (Turner's syndrome) was there mosaicism in skin fibroblasts which was not detected in leukocyte cultures. In another patient (pseudohermaphrodite), mosaicism was present in leukocytes only. It is concluded that very few instances of sex chromosome mosaicism will escape detection if leukocyte cultures only are carried out. This finding is confirmed by the fact that in various reported cytogenetic studies involving patients with Turner's syndrome, the incidence of mosaicism, as in the present study, has been about 1:3, whether leukocytes alone or leukocytes plus cells from other tissues were studied.