Maternal disomy and Prader-Willi syndrome consistent with gamete complementation in a case of familial translocation (3;15) (p25;q11.2).
Maternal uniparental disomy (UPD) for chromosome 15 is responsible for an estimated 30% of cases of Prader-Willi syndrome (PWS). We report on an unusual case of maternal disomy 15 in PWS that is most consistent with adjacent-1 segregation of a paternal t(3;15)(p25;q11.2) with simultaneous maternal meiotic nondisjunction for chromosome 15. The patient (J.B.), a 17-year-old white male with PWS, was found to have 47 chromosomes with a supernumerary, paternal der(15) consisting of the short arm and the proximal long arm of chromosome 15, and distal chromosome arm 3p. The t(3;15) was present in the balanced state in the patient's father and a sister. Fluorescent in situ hybridization analysis demonstrated that the PWS critical region resided on the derivative chromosome 3 and that there was no deletion of the PWS region on the normal pair of 15s present in J.B. Methylation analysis at exon alpha of the small nuclear ribonucleoprotein-associated polypeptide N (SNRPN) gene showed a pattern characteristic of only the maternal chromosome 15 in J.B. Maternal disomy was confirmed by polymerase chain reaction analysis of microsatellite repeats at the gamma-aminobutyric acid receptor beta3 subunit (GABRB3) locus. A niece (B.B.) with 45 chromosomes and the derivative 3 but without the der(15) demonstrated a phenotype consistent with that reported for haploinsufficiency of distal 3 p. Uniparental disomy associated with unbalanced segregation of non-Robertsonian translocations has been reported previously but has not, to our knowledge, been observed in a case of PWS. Furthermore, our findings are best interpreted as true gamete complementation resulting in maternal UPD 15 and PWS.
Department of Pathology, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire 03767, USA. jonathan.p.park@hitchcock.org
J P
JP
Park
J B
JB
Moeschler
V H
VH
Hani
A B
AB
Hawk
D R
DR
Belloni
W W
WW
Noll
T K
TK
Mohandas
D000293:Adolescent; D002884:Chromosomes, Human, Pair 15; D002893:Chromosomes, Human, Pair 3; D019175:DNA Methylation; D005260:Female; D005816:Genetic Complementation Test; D018392:Genomic Imprinting; D005854:Germ Cells; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D018895:Microsatellite Repeats; D010375:Pedigree; D011218:Prader-Willi Syndrome / Q000235:genetics*; D014178:Translocation, Genetic