TETRASOMY-9P - TISSUE-LIMITED IDIC(9P) IN A CHILD WITH MILD MANIFESTATIONS AND A NORMAL CVS RESULT - REPORT AND REVIEW

Supernumerary isochromosomes resulting in autosomal tetrasomy are rare and have been described only for 12p, 18p, and 9p. Nineteen previous cases of tetrasomy 9p have been reported, and in 6 cases, tissue-speci fic mosaicism was implied with the i(9p) cell line present exclusively or predominantly in blood. We report on an infant who had apparently normal chromosomes (46,XY) on CVS. He was referred for genetic evaluat ion because of mild developmental delay and minor anomalies. In 75% of blood cells he had an extra isodicentric 9p chromosome (pter --> q12 --> pter). The interpretation of tetrasomy 9p was confirmed by elevate d GALT activity. No tetrasomy 9p cells were seen in 100 skin fibroblas ts. This case demonstrates the tissue specific mosaicism in tetrasomy 9p which rendered the anomaly undetectable by CVS. It also demonstrate s the mild end of the clinical spectrum associated with tetrasomy 9p. (C) 1993 Wiley-Liss, Inc.