Genetic analyses were performed in a male patient with suspected Prader-Willi 
syndrome who presented with hypogonadism, excessive eating, central obesity, 
small hands and feet and cognition within the low normal range. However, he had 
no neonatal hypotonia or feeding problems during infancy. Chromosome analysis 
showed a normal male karyotype. Further analysis with array-CGH identified a 
mosaic 847 kb deletion in 15q11-q13, including SNURF-SNRPN, the snoRNA gene 
clusters SNORD116 (HBII-85), SNORD115, (HBII-52), SNORD109 A and B (HBII-438A 
and B), SNORD64 (HBII-13), and NPAP1 (C15ORF2). MLPA confirmed the deletion and 
the results were compatible with a paternal origin. Metaphase-FISH verified the 
mosaicism with the deletion present in 58% of leukocytes analyzed. Three smaller 
deletions in this region have previously been reported in patients with 
Prader-Willi syndrome phenotype. All three deletions included SNORD116, but only 
two encompassed parts of SNURF-SNRPN, implicating SNORD116 as the major 
contributor to the Prader-Willi phenotype. Our case adds further information 
about genotype-phenotype correlation and supports the hypothesis that SNORD116 
plays a major role in the pathogenesis of Prader-Willi syndrome. Furthermore, it 
examplifies diagnostic difficulties in atypical cases and illustrates the need 
for additional testing methods when Prader-Willi syndrome is suspected.