11 The partial deletion of the long arm of the paternal chromosome 15 is a common marker of this disease, (12) though it can also present as a maternal uniparental disomy
Maternal uniparental disomy
accounts for further 20%.
5 , and 10% have maternal uniparental disomy
for chromosome 7 .
These mechanisms include a paternally derived de novo deletion of this region (approximately 75%-80%), maternal uniparental disomy
(UPD) of chromosome 15 (approximately 20%-25%), or paternal imprinting defects that silence paternal alleles (approximately 1%).
This form is referred to as maternal uniparental disomy, and affected individuals present with slightly milder symptoms.
In the population of persons with PWS resulting from maternal uniparental disomy, reduced skin picking was seen but there was an increase in affective, psychotic, and autistic symptoms (Boer et al.
But 28% of these cases are caused by maternal uniparental disomy
which means that both chromosome 15's have been derived from the mother, a defect that can only be ascertained with molecular testing.
Do patients with maternal uniparental disomy for chromosome 7 have a distinct mild Silver-Russell phenotype?
A narrow segment of maternal uniparental disomy of chromosome 7q31-qter in SilverRussell syndrome delimits a candidate gene region.
Approximately 70% of PWS cases are associated with a de novo paternally derived deletion, ~25% with maternal uniparental disomy
15, and the rest with deletions or epimutations in the imprinting center or from chromosome 15q translocations (5-7).
2-q13 deletion on the paternally inherited chromosome 15, whereas 25% have maternal uniparental disomy
(UPD), <5% have an imprinting center sequence variant, and 1% have a structural chromosome rearrangement involving 15g11.
PWS results from loss of imprinted genes from the paternally inherited chromosome as a result of either interstitial deletion (-70% of cases) or maternal uniparental disomy
(UPD; -30% of cases) (1-4).