Trisomy 18 in an 11 year old girl.

A case of trisomy 18, confirmed by G banded chromosome analysis, is reported in an eleven year old Australian girl. There is no cytogenetic evidence of mosaicism in the propositus or her parents. The patient's salient clinical features are severe mental and motor retardation with microcephaly, kyphoscoliosis and various congenital anomalies. She has very mild congenital heart disease. She has been totally institutionalised and has required constant medical care. Comparison of her condition with other long-term survivors with trisomy 18 reported in the literature, and also considered to be non-mosaic, reveals many similar features. However, no pattern emerges as to why these rare patients have survived.