An abnormal karyotype consisting of 48 chromosomes has been found in a 16-year-old boy with severe psychomotor retardation and congenital anomalies. The two extra chromosomes: a 15q - and a small metacentric marker appear as derivatives of chromosome 15(48, XY, + 15q -, + mar(15). The healthy father has a mosaic chromosome constitution 46, XY/47, XY, + mar(15) and this additional chromosome is also present in the propositus. It is suggested that the presence of the extra chromosome in the father's germ cells may play a role in the production of the additional 15q - chromosome responsible for the clinical syndrome of the propositus.
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