Prader-Willi syndrome is a disorder which affects 1 in 15000 births and is characterised by:
- neonatal hypotonia
- behavioural disturbance, particularly hyperphagia
- mild-to-moderate mental retardation
60% of cases have a small deletion of the paternal chromosome 15q11-13. The majority of the remainder have two apparently normal apparently normal (but maternally inherited) chromosome 15s (See genetics section for more details).