Kinetic form discrimination in Prader-Willi syndrome

Discrimination of the shape of motion-produced forms generated by random el ements (i.e. second-order stimuli varying in element density and temporal c orrelation) was tested in four groups: (1) subjects with Prader-Willi syndr ome (PWS), chromosome 15q deletion subtype; (2) subjects with PWS, uniparen tal maternal disomy (UPD) subtype; (3) equivalent non-PWS controls; and (4) normal controls. The performance of the normal controls exceeded that of a ll other groups (78% correct, P < 0.009). The PWS deletion (66%) and the eq uivalent control groups (59%) did not differ (P < 0.95). The UPD group perf ormed significantly less well (38%, P < 0.04) than all the other groups. Th e performance of the PWS deletion and equivalent control groups is consiste nt with other data indicating that these populations encounter difficulty m eeting the processing demands posed by second-order stimuli. The inferior p erformance of the UPD group may be attributed to receiving two active allel es of a maternally expressed gene influencing neural development. One candi date is the ubiquitin protein ligase gene (UBE(3)A), which is maternally ex pressed only and localized to the 15q region. Other possibilities include t he requirement of a paternally expressed gene, residual mosaic trisomy 15 i n the brain tissue or complex interactions including specific ratios of dif ferentially spliced gene products.