Prader-Willi syndrome is an example of genetic imprinting where the phenotype depends on whether the deletion occurs on a gene inherited from the mother or father:

• Prader-Willi syndrome if gene deleted from father
• Angelman syndrome if gene deleted from mother

Epidemiology

1 in 15,000 - 20,000

Clinical Features

• Constant insatiable hunger that leads to obesity
• Poor muscle tone as an infant (hypotonia)
• Mild-moderate learning disability
• Hypogonadism
• Fairer, soft skin that is prone to bruising
• Mental health problems, particularly anxiety
• Dysmorphic features
• Narrow forehead
• Almond shaped eyes
• Strabismus
• Thin upper lip
• Downturned mouth