NEW CASE OF MOSAIC TETRASOMY 9P WITH ADDITIONAL NEUROMETABOLIC FINDINGS

Tetrasomy 9p is a rare chromosomal aberration that was described in 28 previous patients, Here we report on a newborn girl who was referred for genetic evaluation because of developmental delay, hypertonicity, microcephaly, minor anomalies, and neurometabolic findings. She had an isochromosome 9p (pter --> p10 --> pter) in 32% of blood cells, The e xtra chromosome was not found in amniocytes. Examination of fibroblast s from different skin biopsies also showed mosaicism in this tissue. I n a first biopsy from the abdominal wall, the cells (n = 50) had a nor mal chromosomal complement. Further analysis of fibroblasts from the l eft forearm showed the isochromosome 9p in 5 out of 8 mitoses, Fluores cence in situ hybridization (FISH), using a whole chromosome 9 probe, confirmed that the extra marker was 9 in origin, Molecular studies sho wed that the isochromosome was of maternal origin. Meiotic nondisjunct ion was followed by centromeric misdivision and postzygotic loss of-th e marker.