Martin-Bell syndrome segregating in a large kindred with normal transmitting males: clinical, cytogenetic, and linkage study.

We report on a large kindred with 10 mentally retarded, fra(X) positive males and 2 normal transmitting males. Clinical findings include variable degrees of facial anomalies, macroorchidism, behavioral characteristics, and cognitive deficiencies. The affected grandsons were fra(X) positive while their obligate carrier mothers and transmitting grandfathers were fra(X) negative. DNA-restriction fragment length polymorphism (RFLP) linkage study was undertaken to find informative markers to identify heterozygotes or hemizygotes. The problems encountered in genetic counselling, by the absence of established criteria for diagnosis, are discussed.