The inheritance of fragile sites: apparent absence of fra(2)(q13) in the parents of three unrelated probands.

We describe the inherited folate sensitive fragile site, fra(2)(q13), in three unrelated mentally retarded children, two of them with different forms of epilepsy. Fra(2)(q13) was detected in one healthy sib of one of the probands. Except for one cell in one of the fathers, fra(2)(q13) could not be detected in any of the six parents, who were repeatedly studied using methods known to induce fragile sites of this type.

The origin of 45,X males.

Maleness in association with the karyotype 45,X is a very rare and hitherto unexplained condition previously described in only four or five patients. This study was carried out to determine whether such males might actually possess Y-chromosomal material. Of the two 45,X males studied, one was found to be a low-grade mosaic with a 46,XY karyotype in less than 3% of fibroblasts; all lymphocytes karyotyped were 45,X.