(See also Overview of Chromosome Disorders Overview of Chromosome and Gene Disorders Chromosomes are structures within cells that contain a person's genes. A gene is a segment of deoxyribonucleic acid ( DNA) and contains the code for a specific protein that functions in one... read more .)
About 70% of people who have Prader-Willi syndrome are missing part of chromosome 15. About 30% of people who have this syndrome have problems with the function of chromosome 15.
Symptoms of Prader-Willi Syndrome
Many symptoms of Prader-Willi syndrome vary according to the child's age. Newborns with the defect feel limp, feed poorly, and gain weight slowly. Eventually these symptoms resolve. Then, between the ages of 1 and 6, appetite increases, often becoming insatiable. Children rapidly gain weight. The hands and feet remain small, and children remain short. Abnormalities of the face include almond-shaped eyes and a mouth with thin upper lips and down-turned corners. Children have bone disorders (such as scoliosis Scoliosis Scoliosis is abnormal curvature of the spine. Scoliosis can be present at birth or can develop during adolescence. Mild forms may cause only mild discomfort, but more severe forms can cause... read more 
and kyphosis Kyphosis Kyphosis is an abnormal curving of the spine that causes a humpback. (See also Overview of Bone Disorders in Children.) The upper back normally curves forward somewhat. Some children have a... read more ). Obsessive-compulsive behaviors Obsessive-Compulsive Disorder (OCD) and Related Disorders in Children and Adolescents Obsessive-compulsive disorder is characterized by recurring, unwanted, intrusive doubts, ideas, images, or impulses (obsessions) and unrelenting urges to do actions (compulsions) to try to lessen... read more are common. Hormonal problems are common, and the function of the reproductive organs is abnormally decreased, which limits growth and sexual development. Boys have undescended testes Undescended testes Undescended testes (cryptorchidism) are testes that remain in the abdomen or the groin instead of descending into the scrotum. Retractile testes (hypermobile testes) have descended into the... read more 
(cryptorchidism) and an underdeveloped penis and scrotum. Intellectual disability Intellectual Disability Intellectual disability is significantly below average intellectual functioning present from birth or early infancy, causing limitations in the ability to conduct normal activities of daily... read more is common. Weight gain often continues into adulthood and is excessive, which can lead to other health problems, such as obesity. Obesity can be severe enough to justify gastric bypass surgery Types Bariatric (weight-loss) surgery alters the stomach, intestine, or both to produce weight loss. In the United States, about 160,000 people have bariatric surgery each year. This number accounts... read more .
Diagnosis of Prader-Willi Syndrome
Chromosomal testing
The diagnosis of Prader-Willi syndrome may be suspected before birth or by the child's physical characteristics after birth. The diagnosis can be confirmed by chromosomal testing. (See also Next-generation sequencing technologies Next-generation sequencing technologies Genetic diagnostic technologies are scientific methods that are used to understand and evaluate an organism's genes. (See also Genes and Chromosomes.) Genes are segments of deoxyribonucleic... read more .)
Treatment of Prader-Willi Syndrome
Sometimes growth hormone
Ongoing research is being done to find treatments that help improve the prognosis for children and adults who have Prader-Willi syndrome. Many research studies show that human growth hormone is beneficial.
