title: Prenatal diagnosis of supernumerary marker 15 chromosomes and exclusion of uniparental disomy for chromosome 15.
abstract: 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.
authors.affiliation: Division of Medical Genetics, Children's Hospital Oakland, 747 Fifty Second Street, Oakland, CA 94609, USA. pcotter@mail.cho.org
authors.forename: P D
authors.initials: PD
authors.lastname: Cotter
authors.forename: C T
authors.initials: CT
authors.lastname: Ledesma
authors.forename: L G
authors.initials: LG
authors.lastname: Dietz
authors.forename: S
authors.initials: S
authors.lastname: Pusso
authors.forename: M M
authors.initials: MM
authors.lastname: Wohlferd
authors.forename: J D
authors.initials: JD
authors.lastname: Goldberg
mesh_terms: D000328:Adult; D000649:Amniocentesis; D002869:Chromosome Aberrations / Q000175:diagnosis* / Q000235:genetics; D025063:Chromosome Disorders; D002884:Chromosomes, Human, Pair 15; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008423:Maternal Age; D011247:Pregnancy; D018566:Pregnancy, High-Risk