Prader-Willi syndrome (PWS) is caused by the loss of expression of imprinted genes in chromosome 15q11-q13 region. Affected individuals exhibit neonatal hypotonia, developmental delay, and childhood-onset obesity. Necdin (NDN), a gene involved in the terminal differentiation of neurons, localizes to this region of the genome and has been implicated as one of the genes responsible for the etiology of PWS. This gene is structurally similar to NDN, is also localized to the PWS chromosomal region, and is paternally imprinted, suggesting a possible role for it in PWS.