Prader-Willi Syndrome

Prader-Willi syndrome is a rare genetic disorder,affecting 1 out of 25,000 births,in which a critical region of chromosome 15,the 15q11-q13 region,is affected.At birth,PWS infants exhibit severe hypotonia that partially improves,explaining in part suckling and swallowing troubles and the delay in psychomotor development.Characteristic facial features and very small hands and feet are frequently observed at this age.After this initial phase,the most striking signs appear:hyperphagia and absence of satiety often lead to severe obesity in affected children.Other endocrine abnormalities in association with the hypothalamic-pituitary abnormalities contribute tO the clinical pictures of short stature due to a growth hormone deficiency and incomplete pubertal development.The degree of cognitive dysfunction varies widely from one child to another.It is associated with learning disabilities and impaired speech and language development worsened by psychological and behavioral troubles.The expert consensus is that diagnosis should be based on clinical criteria (Holm's criteria of 1993,revised in 2001) with confirmation by genetic study.Early diagnosis,early multidisciplinary care and growth hormone treatment have greatly improved the quality of life of these children.In adults,complications particularly linked to obesity and problems of autonomy are still very important. Key words: Prader-Willi syndrome; SNRPN gene;  Genomic imprinting;  FISH