Three cell line mosaicism involving structural and numerical abnormalitiesof chromosome 18 in a 3.5-year-old girl: 47,XX,+18/47,XX,+del(18)(q22)/46,XX

We report on a 3.5-year-old girl with a mosaic karyotype including full tri somy 18, normal cells and a majority of cells with partial trisomy involvin g an extra chromosome 18 deleted at band q22, She had cardiac and CNS anoma lies, dysmorphic facial features, failure to thrive and developmental delay . A gastrostomy tube was placed at 2 years of age. The combination of impro ved nutrition and optimal developmental therapy has led to her sitting supp orted, attempting to stand and enhancement of her cognitive and non-verbal communication abilities. Molecular investigation of the patient and her par ents using microsatellite analysis has led to the conclusion that, as expec ted, the additional. copy of chromosome 18 constituting the full trisomic c ell line is maternal meiosis I in origin. The data, however, indicate that in the trisomic cell Line containing the deleted chromosome 18q, the struct urally abnormal 18 was of paternal origin. We think this case is the first described with both structural and numerical trisomic mosaicism involving c hromosome 18 in a liveborn infant, We propose a mechanism of origin. and re view the literature, comparing the clinical presentation of this case with individuals having full or partial trisomy 18, (C) 2001 Wiley-Liss, Inc.