Prader-Willi syndrome is disease that is present from birth (congenital). People with this condition are obese, have reduced muscle tone and mental ability, and have sex glands that produce little or no hormones.

Prader-Willi syndrome is caused by a gene missing on part of chromosome 15. Normally, your parents each pass down a copy of this chromosome. Most patients with Prader-Willi syndrome are missing the genetic material on part of the father's chromosome. The rest of patients with this condition often have two copies of the mother's chromosome 15.

The genetic changes occur randomly. Patients usually do not have a family history of the condition.

Newborns with this disorder:

• Are small for gestational age
• Have genitals that are not well developed (in boys, the testicles cannot be felt in the scrotum)
• Have problems sucking and swallowing, and often do not gain weight
• May seem floppy and feel like a "rag doll" when held
• Often have a weak cry
• Show changes in the face, such as "almond-shaped" eyes and a small, downturned mouth

Other symptoms include:

• Irregular areas of skin that look like bands, stripes, or lines
• Llimb (skeletal) abnormalities
• Very small hands and feet compared to the body

Affected children have an intense craving for food and will do almost anything to get it. This results in uncontrollable weight gain and morbid obesity. Morbid obesity may lead to lung failure, which includes low blood oxygen levels, right-sided heart failure, and death.

Signs of Prader-Willi syndrome may be seen at birth. Newborns with the condition are often small and very floppy. Male infants may have undescended testicles.

As the child grows older, laboratory tests may show signs of morbid obesity, such as:

• Abnormal glucose tolerance
• Above normal level of the hormone insulin in the blood
• Failure to respond to luteinizing hormone releasing factor
• High carbon dioxide levels
• Lack of oxygen supply

There may also be signs of right-sided heart failure and knee and hip problems.

The person will need the right education for his or her IQ level. Controlling weight will allow for a much more comfortable and healthy life.

• Bone (orthopedic) problems
• Diabetes
• Right-sided heart failure

Call your health care provider if your child has symptoms of this condition. The disorder is frequently suspected at birth.

Saitta SC, Ackai EH. Specific chromosome disorders in newborns. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 20.

McCandless SE; Committee on Genetics. Clinical report -- health supervision for children with Prader-Willi syndrome. Pediatrics. 2011; 127(1):195-204.