Hi doctors, can you tell me what is prader-willi syndrome?

A genetic disorder: Usually from a deletion of a gene on the chromosome 15 inherited from the father, it can also come from having both chr 15's from the mother or both acting as if they came from mother. Infants have low muscle tone ; trouble gaining weight; food craving ; weight gain start about 18 mos. They have congenital anomalies, intellectual disability, compulsive behavior, ; medical problems due to obesity.