Familial tiny 9p/20p translocation: 9p24. The critical segment for monosomy 9p syndrome.

The presence of a chromosomal translocation was suggested in a large kindred with several cases of mental retardation. Chromosome analysis by means of a high resolution technique revealed a translocation of a tiny terminal portion of 9p onto 20p in the presumptive balanced translocation carriers. Five of the affected family members demonstrated monosomy of the terminal portion of 9p. Their clinical features fitted well to the known 9p- syndrome. The breakpoint on 9p is in the distal part of band 9p23. This family confirmed the assumption that the critical segment for monosomy 9p syndrome is located within the terminal band 9p24.