Prader-Willi (PRAH-dur VIL-e) syndrome is a rare disorder present at birth that results in a number of physical, mental and behavioral problems. A key feature of Prader-Willi syndrome is a constant sense of hunger that usually begins at about 2 years of age.People with Prader-Willi syndrome want to eat constantly because they never feel full (hyperphagia) and usually have trouble controlling their weight. Many complications of Prader-Willi syndrome are due to obesity.If you or your child has Prader-Willi syndrome, a team of specialists can work with you to manage symptoms, reduce the risk of developing complications and improve quality of life. Signs and symptoms of Prader-Willi syndrome generally occur in multiple phases. Signs that may be present from birth include:Poor muscle tone. A primary sign during infancy is poor muscle tone (hypotonia). Babies may rest with their elbows and knees loosely extended instead of fixed, and they may feel floppy or like rag dolls when they're held.Distinct facial features. Children may be born with almond-shaped eyes, a narrowing of the head at the temples, a turned-down mouth and a thin upper lip.Failure to thrive. Infants may have a poor sucking reflex due to decreased muscle tone. Because poor sucking makes feeding difficult, they tend to gain weight slowly.Lack of eye coordination (strabismus). The child's eyes may not move together — they may cross or wander to the side.Generally poor responsiveness. A baby may seem unusually tired, respond poorly to stimulation, have a hard time waking up or have a weak cry.