The small nuclear ribonucleoprotein polypeptide N (SNRPN) gene is regarded as 
one of the candidates for Prader-Willi syndrome (PWS). We describe two sibs with 
typical PWS presenting deletion of SNRPN detected by fluorescence in situ 
hybridization (FISH). Neither a cytogenetically detectable 15q12 deletion nor a 
deletion for the D15S11, D15S10, and GABRB3 cosmid probes were found in either 
patient. This implies a smaller deletion limited to the PWS critical region. 
FISH with a SNRPN probe will permit analysis of PWS patients with limited 
deletions not detectable with other probes.