Mosaic trisomy of a small r(1) with an abnormal phenotype

Cytogenetic studies of a mildly dysmorphic 10-year-old male with mild devel opmental delay and learning difficulties revealed mosaicism. for a supernum erary ring chromosome in approximately half of the cells. The karyotype of this patient was established as 47,XY,+r[15]/46,XY[15].ish r(1) (D1Z7+,wcp1 -). Although the presence of euchromatic material was shown by C banding, t he lack of hybridization with the whole chromosome paint 1 (wep1) probe sug gests that few unique sequences are contained in the ring and that these se quences likely explain the child's dysmorphic features and developmental de lay. A review of the literature, including the present case, suggests that the significance of euchromatin in supernumerary r(1) as determined by both C banding and fluorescence in situ hybridization (FISH) with chromosome I painting probes can be used as a prognostic indicator for potential severit y of the clinical phenotype. (C) 2001 Wiley-Liss, Inc.