In all PWS subjects, copy number reduction was observed for genes situated on the long arm of chromosome 15q11-q13 between break point 2 (BP2) and BP3, encompassing NECDIN, MRKN3, and MAGEL2. Notably, the distinction between the two genotypes relied on the profiling of NIPA1 and TUBGCP5 genes positioned between BP1 and BP2. Here, TUBGCP5 is linked to Prader-Willi syndrome.