Prenatal diagnosis of supernumerary marker 15 chromosomes and exclusion of uniparental disomy for chromosome 15

✍ Scribed by Philip D. Cotter; Carmelita T. Ledesma; Lisa G. Dietz; Sharon Pusso; Monica M. Wohlferd; James D. Goldberg

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 252 KB
• Volume: 19
• Category: Article
• ISSN: 0197-3851
• DOI: 10.1002/(sici)1097-0223(199908)19:8<721::aid-pd616>3.0.co;2-m

✦ Synopsis

Supernumerary marker chromosomes (SMC) were identified in amniocytes from two unrelated fetuses. Fluorescence in situ hybridization (FISH) characterization of the SMC showed they were derived from chromosome 15; SMC(15). Parental karyotyping demonstrated the SMC(15) to be de novo in one fetus and paternally derived in the other. Previous reports showed that the presence or absence of the Prader-Willi/ Angelman syndrome (PWS/AS) critical region, loci D15S11 and distal, in a SMC(15) was associated with an abnormal or normal phenotype, respectively. FISH analysis demonstrated both SMC(15) lacked the D15S11 locus. Because SMC(15) were found at an increased incidence in patients with PWS/AS, we performed methylation analysis at the SNRPN locus to exclude a deletion or uniparental disomy (UPD) of chromosome 15. Both probands showed biparental inheritance at this locus. Based on the FISH and molecular analyses, both fetuses were predicted to have a normal phenotype. The pregnancies were continued and both probands are phenotypically and developmentally normal. These cases illustrate the importance of a combination of family studies, FISH characterization and molecular analyses in SMC(15) identified prenatally. In particular, any chromosome 15 rearrangement identified at prenatal diagnosis should be considered a candidate for UPD15 studies.