Partial 11q trisomy syndrome.

The syndrome caused by partial trisomy for 11q is reviewed on the basis of a patient of our own and 20 cases (including a stillbirth) from the literature. The main symptoms are presented in Tables 1 and 2. The syndrome can be suspected when, in addition to mental retardation, the following characteristics are present: short nose, long philtrum, micrognathia, retracted lower lip, and micropenis in males. In 15 families, the mother was a balanced translocation carrier and in four the father. The translocation had arisen de novo in two patients. The chromosome number was 46 in 13 affected individuals (including the stillbirth) and 47 in eight. In seven of the latter patients the other translocation chromosome was 22, and in one, chromosome 9. The breakpoints on 11q ranged from 11q121 to 11q232 (Fig. 5). There is no apparent correlation between the length of the trisomic segment and the number or severity of the symptoms (Table 2). This could be explained by assuming that most, if not all, symptoms are caused by trisomy for the Q-dark region distal to 11q232, whereas trisomy for the rest of the 11q up to q121 has few phenotypic effects. These observations support the idea that Q-dark segments, and especially certain hot spots, have a high gene density in contrast with Q-brighter regions.