[Do all cases of trisomy 18 with long survival (beyond 10 years) show mosaicism in fibroblasts? (author's transl)].

Description of a young girl aged 16 1/2 years who presents the typical features of trisomy 18 : small height, microdolichocephaly, anti-mongoloid palpebral fissures, micrognathia, microstomia, arched palate, malformed ears, atrophy of thenars and hypothenars, clinodactyly of fifth fingers and abortive cutaneous syndactyly between IV and V. At the lower limbs, there is a shortening of the right leg, an atrophy of the calves, as well as genua valga and bilateral pes excavatus with dorsiflexion of the toes. The gait is rigid with enlarged basis of sustentation. The results of the cardiac examination point to a minor ventricular septal defect. The development of secondary sexual characters (breasts and body hair) corresponds to the puberal age; the large pudendal lips are hypoplastic. The X-rays show a double left kidney. There is a very severe oligophrenia (I.Q. = 20). Cytogenetic examinations showed a typical trisomy 18 in 100% of observed lymphocytes, while the analysis of cutaneous fibroblasts revealed a mosaicism with 87% of trisomic cells. Out of 11 cases of trisomy 18 with long survival from the literature only 3 cases were of mosaic type. The authors assume that this small number of mosaic cases in trisomy is probably due to the fact that no examination of fibroblasts has been carried out in the seven other cases.