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Intellectual Disabilities
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Childhood Mental Disorders and Illnesses

Genetic Causes of Intellectual Disabilities: Prader-Willi Syndrome (PWS)

Tammy Reynolds, B.A., C.E. Zupanick, Psy.D. & Mark Dombeck, Ph.D.

Prader-Willi Syndrome (PWS) is also referred to as hypotonia-hypomentia-hypogonadism-obesity syndrome (HHHO). It is a genetic disorder involving a malfunction of chromosome 15. Some explanation is necessary to unpack this unwieldy term:

  • Hypotonia describes a condition where muscle tone is weak. The abnormality is apparent in infancy. It is indicative of a problem in the central nervous system.
  • Hypomentia refers to intellectual disability or learning disabilities.
  • Hypogonadism describes a condition characterized by inefficient, weak secretion of male or female hormones. This results in delayed sexual development and infertility.
  • Obesity pertains to excessive weight. Obese individuals are typically at least thirty pounds over the recommended weight for their height.

Prader-Willi syndrome is not associated with any particular gender, race, or socioeconomic group. Only two percent of cases appear to be inherited. The rest seem to from result of random mutation.

Because chromosome 15 is closely tied to obesity, obesity is a common symptom. Initially infants do not gain weight, as they should. This is due to weak facial muscles that interfere with nursing. However, as children grow older they develop a great interest in food. They are not able to control urges to binge-eat. Their lack of growth worsens their weight problem.

The first signs of the condition are based on characteristic appearance and behavior. Once the disorder is suspected, genetic testing can confirm the diagnosis. Facial features include almond-shaped eyes that may be crossed, full cheeks, and a narrow face. The mouth is small and the corners of the mouth turn downwards. The small mouth is accentuated by a thin upper lip.

Medical problems are related to obesity. These individuals often develop diabetes and heart problems. Muscle mass is insufficient. Sometimes growth hormones are given to help increase muscle mass. Diet, exercise, and weight maintenance programs are also helpful. Prader-Willi syndrome is tied to milder forms of intellectual disability. Behavioral problems include tantrums, obsessive/compulsive tendencies, and skin picking.