 Studies of human and mouse model systems have shown deletion of the 29 copies of the C/D box snoRNA SNORD116 (HBII-85) to be the primary cause of PWS.It is traditionally characterized by hypotonia, short stature, hyperphagia, obesity, behavioral issues (specifically obsessive–compulsive disorder-like behaviors), small hands and feet, hypogonadism, and mild intellectual disability.However, with early diagnosis and early treatment (such as with growth hormone therapy), the prognosis for persons with PWS is beginning to change.