Assessment of SNRPN expression as a molecular tool in the diagnosis of Prader-Willi syndrome

Background: Prader-Willi syndrome (PWS) is associated with lesions of the paternal chromosome 15q11-13. Recently, loss of expression of a paternally expressed gene in this region, SNRPN has been proposed as a molecular hallmark of PWS. The goal of this study was to determine the diagnostic accuracy of SNRPN expression in a well-characterized cohort of PWS patients. Methods: SNRPN expression was analyzed by reverse transcription coupled to polymerase chain reaction (RT-PCR). RNA was isolated from peripheral blood leukocytes and subjected to multiplex RT-PCR in which expression of SNRPN and a constituitively expressed internal control gene were analyzed. The amplified products were electrophoresed in agarose gels and visualized by ethidium bromide staining. Results: Multiplex RT-PCR was applied to RNAs isolated from 30 normal control subjects and 30 well-characterized PWS patients. All control patients expressed the SNRPN and internal control genes. In contrast, all 30 PWS patients demonstrated loss of SNRPN expression, with integrity of RNA being demonstrated by the presence of internal control gene expression. Conclusions: Loss of SNRPN expression appears to be a consistent finding in PWS. Expression analysis of SNRPN offers a novel approach for the diagnostic evaluation of PWS that is robust and can be performed in a single day.