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 p aternal chromosome 15q11-13. Recently, loss of expression of a paternally e xpressed gene in this region, SNRPN has been proposed as a molecular hallma rk 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 a nd a constituitively expressed internal control gene were analyzed. The amp lified products were electrophoresed in agarose gels and visualized by ethi dium bromide staining. Results: Multiplex RT-PCR was applied to RNAs isolated from 30 normal contr ol subjects and 30 well-characterized PWS patients. All control patients ex pressed the SNRPN and internal control genes. In contrast, all 30 PWS patie nts demonstrated loss of SNRPN expression, with integrity of RNA being demo nstrated 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 diagnost ic evaluation of PWS that is robust and can be performed in a single day.