Partial trisomy of the short arm of chromosome 3 (3p25 to 3pter). A distinct clinical entity.

Two profoundly mentally retarded brothers with partial trisomy for the distal part of the short arm of chromosome 3 (3p25 to 3pter) are described. Their anomaly arose as a segregation product of a balanced t(3p-;18q+) translocation in the mother. Compared with the other cases of partial 3p trisomy reported up to now, the present patients display a similar craniofacial dysmorphism with hypertelorism, broad nasal tip, short upper lip with prominent philtrum, and a large mouth with down-turned corners. Other stigmata, such as a prominent, high forehead with frontal bossing and full cheeks, were present during childhood but progressively disappeared.