Classic Prader-Willi Syndrome Phenotype Caused by an Atypical Deletion in the 15q11 Region Not Involving the SNORD Genes.

Prader-Willi syndrome (PWS) is an uncommon genetic disorder caused by the lack of expression of a cluster of genes located in the 15q11.2q13 region, which are normally expressed only from the paternally-inherited allele due to genomic imprinting. PWS can result from a deletion of the 15q11.2q13 region on the paternally-inherited chromosome 15, maternal uniparental disomy, or imprinting defects. We report a patient with an atypical deletion within 15q11.2q13 and a PWS phenotype, including hypotonia, feeding difficulties, short stature, developmental delay, and dysmorphisms. She has a deletion from TUBGCP5 to SNURF-SNRPN (including the imprinting center) but not the SNORD region. These types of reports are crucial for further supporting the established role of the imprinting center in the pathophysiology and critical region of PWS.