Understanding the eating disorder affecting people with Prader-Willi syndrome

The propensity to severe over-eating, which may lead to life-threatening obesity, is characteristic of people born with the Prader Willi Syndrome (PWS). This syndrome is caused by the loss of expression of either a specific or a few specific genes on chromosome 15 at q11-13. In the case of PWS this is due to a deletion affecting chromosome 15 of paternal origin and the fact that specific genes at the same locus, but on chromosome 15 of maternal origin, are imprinted and therefore not expressed. The characteristic tendency to over-eat is observed from early childhood and, particularly in later life, can lead to severe obesity if unsupervised access to food is allowed. The normal satiety response to the intake of calories appears both impaired and delayed and therefore eating continues. The pathophysiology, which underpins this abnormal eating behaviour, is likely to relate to the functioning of specific hypothalamic nuclei. PWS is an example of what has been called a 'behavioural phenotype'. The research task is to link the observed genetic abnormalities to brain function and in turn to the eating behaviour. This paper examines these links and proposes a conceptual model to help in the understanding and management of the excessive eating behaviour.