Schaaf-Yang syndrome (SHFYNG) (MIM #615547) is a genetic neurodevelopmental disorder caused by mutations in the MAGEL2 gene located on chromosome 15.
This is a maternally imprinted, paternally expressed gene, such that the copy inherited from the father will be expressed while the copy from the mother is silenced. If a mutation exists on the paternal copy, it will be expressed, with potentially deleterious effects.
The subsequent clinical phenotypes are typically neonatal hypotonia, contractures of small joints, feeding difficulties requiring assisted feeding techniques, developmental delay/intellectual disability, hypogonadism, and autism spectrum disorder, among others.
The phenotypic severity seen in Schaaf-Yang syndrome ranges from fetal akinesia with pre-or perinatal mortality to milder phenotypes that are mostly neurodevelopmental, with contractures of only the small finger joints.