Prader-Willi syndrome with a karyotype 47,XY,+min(15)(pter->q11.1:) and maternal UPD 15 - Case report plus review of similar cases

Prader-Willi (PWS) and Angelman (AS) are syndromes of developmental impairment that can result either from a 15q11-q13 deletion, paternal uniparental disomy (UPD), imprinting, or UBE3A mutations. A small cytogenetic subset of PWS and AS patients are carriers of a so-called small supernumerary marker chromosome (sSMC). Here, we report on an previously unreported PWS case with a karyotype 47,XY,+min(15)(pter->q11.1:) plus maternal heterodisomic UPD 15. A review of the literature revealed, that for both, PWS and AS patients, cases with (1) a sSMC plus microdeletion of the PWS/AS critical region, (2) inv dup(15) plus uniparental disomy (UPD) 15 and (3) cases without exclusion of a microdeletion an UBE3A mutation or UPD are described. The present case as well as the review of similar cases provides further evidence for the necessity to test UPD in prenatal cases with a de novo sSMC and in postnatal cases with otherwise unexplainable clinical phenotype.