The book follows a process of discovery that included getting to know many people with Prader—Willi syndrome (PWS) and their families through the undertaking of a population-based study of children and adults with PWS living in the then Anglia and Oxford Health Region of the UK. The aims of this study were to systematically investigate many aspects of the syndrome free from the selection biases that may have influenced previous clinic and volunteer-based studies. The in-depth knowledge gained from this ‘Cambridge study’ through direct contact with people with PWS, their families and other carers, and the integration of this knowledge with that in the literature, has led in turn to new hypotheses and new interpretations of some aspects of PWS.

Prader—Willi syndrome is a relatively rare, genetically determined complex neurodevelopmental disorder. People with the syndrome have their own individual characteristics but share in common particular physical features, specific cognitive strengths and weaknesses, and a propensity to particular behaviours and mental health problems that change with age and together make up the early and later physical and behavioural ‘phenotypes’ of the syndrome.

The genetics of PWS are still not fully elucidated and are clearly more complex than originally anticipated. Candidate gene(s), located on the long arm of chromosome 15 between bands 11 to 13 (15q11—q13), which are maternally imprinted and only expressed when inherited from the father, have been identified but the precise gene or genes whose absence of expression leads to PWS are still not known.