NIPA1 and Prader-Willi syndrome: 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.