Loss of paternally inherited allele from chromosome 15. Gene from mom is normally silent (maternal imprinting) and paternal gene is deleted/mutated.

Etiology:- 25% maternal uniparental disomy (two maternally imprinted genes are received)- Paternal microdeletion

- Affects males and females

Clinical features:- Mental retardation- Short stature- Neonatal hypotonia- Hyperphagia/obesity- Hypogonadism- Small hands and feet- Dysmorphic facies