Sporadic occurrence of nondeletion Prader-Willi syndrome in two cases: a female with maternal uniparental disomy and a male with complex chromosomal rearrangement.

We report here two cases of nondeletion Prader-Willi syndrome (PWS). Case 1 is a 9-yr-old female patient with classical features of the syndrome and cytogenetically normal chromosome 15. DNA analysis using polymorphic probes for Prader-Willi Critical Region (PWCR) showed absence of paternal alleles while maternal uniparental isodisomy (UPisoD) was confirmed. This is the first report of nondeletion PWS with uniparental disomy (UPD) in the population of Kuwait. The second case with Prader-Willi syndrome-like features had normal chromosome 15 but showed familial complex chromosomal rearrangement (CCR) involving chromosomes 13, 19, and 20 inherited from his mother. No paternal deletion or UPD disomy was observed after DNA molecular analysis. This is a case of "atypical" PWS with no cytogenetic or molecular abnormality for PWCR. The two cases represent two different mechanisms associated with nondeletion PWS.