Definition
Prader-Willi syndrome is a congenital (present from birth) disease characterized by obesity, decreased muscle tone, decreased mental capacity and hypogonadism.

What is Prada-Willi Syndrome?
Prader-Willi is caused by the deletion of a gene on chromosome 15. For unknown reasons, only the copy of this gene on chromosome 15 that is received from the father is active. The maternal copy of this gene is turned off in all people. When there is a deletion of this gene on the only copy received from the father, the disease occurs. This is because the patient is left with only the maternal copy, which is inactive in all people.

Signs of Prader-Willi may be seen at birth. New infants with the condition are often small and very floppy (hypotonic). Male infants may have undescended testicles. The growing child often exhibits slow mental and delayed motor development, increasing obesity and characteristically small hands and feet.

Rapid weight gain may occur during the first few years because the patient develops uncontrollable hunger, which in turn leads to obesity, often respiratory failure with hypoxia (low blood oxygen levels) and corpulmonale (right-sided heart failure). Mental development is slow, and the IQ seldom exceeds 80.

Symptoms/ Warning Signs