A Prader-Willi syndrome patient is described who has a de novo balanced tra
nslocation, (4;15)(q27;q11.2)pat, with breakpoints lying between SNRPN exon
s 2 and 3. Parental-origin studies indicate that there is no uniparental di
somy and no apparent deletion. This patient expresses ZNF127, SNRPN exons 1
and 2, IPW, and D15S227E (PAR1) but does not express either SNRPN exons 3
and 4 or D15S226E (PARS), as assayed by reverse transcription-PCR, of perip
heral blood cells. Methylation studies showed normal biparental patterns of
inheritance of loci DN34/ZNF127, D15S63, and SNRPN exon 1. Results for thi
s patient and that reported by Sun et al. support the contention that an in
tact genomic region and/or transcription of SNRPN exons 2 and 3 play a pivo
tal role in the manifestations of the major clinical phenotype in Prader-Wi
lli syndrome.