NDN and Prader-Willi syndrome: In detail, PWS is caused by a loss of expression of imprinted paternally inherited genes on chromosome 15q11.2-q13, including five functional genes (MKRN3, MAGEL2, NDN, NPAP1, and SNURF-SNRPN) and a cluster of small nucleolar RNA genes (Wong et al., 2020).