Supernumerary marker 15 chromosome in a patient with Prader-Willi syndrome [1]

BORELINA, D.; ESPERANTE, S.; GUTNISKY, V.; FERREIRO, V.; FERRER, M.; GILIBERTO, F.; FRECHTEL, G.; FRANCIPANE, L.; SZIJAN, IRENE

CLINICAL GENETICS

WILEY-BLACKWELL PUBLISHING, INC

Año: 2004 vol. 65 p. 242 - 243

0009-9163

The supernumerary marker 15 chromosome(SMC 15) represents 50% of the marker chromosomes. While some include euchromatin (bandsq11–q13) and are linked to severe mental retardation, others without euchromatin associate with anormal phenotype in most cases but rarely withPrader–Willi syndrome (PWS) (1). This is a neurobehavioral disorder due to developmental impairment. PWS results from the loss of expression ofimprinted genes in the paternal chromosome15q11-q13, through several mechanisms such asdeletions or uniparental disomy (UPD) (2).Herein, we studied a 13-year-old girl with acharacteristic PWS phenotype and a smallSMC(15). She was one of two dizygotic twins,underwent a severe neonatal hypotonia followedby hyperphagia, obesity, hypogonadism, and mental retardation, and hypopigmentation was absent.One distinctive feature was an early-onset type 1diabetes. Cytogenetic results showed 47,XX,þmar,the karyotypes of her parents and the healthy twinbeing normal thus indicating a de novo origin of theSMC(15). It was monocentric and monosatellitedby GTG (Trypsin-Giemsa staining) and Ag/NORstainings (Fig. 1a). Fluorescence in situ hybridization (FISH) analysis revealed the 15 alpha satellite(D15Z1) signal; neither the probes for SNRPN orD15S10 nor that for PML polymorphisms (15q22)showed any signal on this SMC(15) (Fig. 1b). Thus,the karyotype was 47,XX,þdel(15)(q11.2).ishdel(15)(D15Z1þ, SNRPN–, D15S10–, PML–)