Genetic Causes of Mental Retardation - Angelman Syndrome

Tammi Reynolds, BA & Mark Dombeck, Ph.D.

Angelman syndrome was first identified in 1965 by Harold Angelman. The syndrome is chromosomal in nature and is associated with neurological problems. The genetic disorder involves the absence or inactivity of a certain group of genes that control ubiquitin, a protein present on chromosome 15q11-13. The abnormal chromosome is typically inherited, but some cases seem to be caused by spontaneous genetic mutation.

The severity of the symptoms varies according to which of the genes are mutated and how profoundly the genes are altered from their normal form. Physical traits associated with Angelman syndrome are not readily apparent at birth. They include a flat-shaped head and a protruding tongue. The circumference of affected individuals' heads tends to be smaller than average as well.

Angelman syndrome infants appear normal, but the syndrome manifests itself in feeding problems that typically arise during the first two months of life. Developmental delays are apparent by the time the baby is six to twelve months old and include significant delays in the acquisition of speech. Movement and balance disorders interfere with the child's development and the child may experience seizures by the time he reaches three years of age.

The condition is marked by developmental delays, communication deficits, and difficulty with walking and standing for extended periods. Communication deficits are profound to the point where many affected individuals never use words. Many individuals with the disorder are hyperactive and have trouble controlling body movements. They often exhibit abrupt, jerky motions and a stiff posture. Excessive and inappropriate laughter is a telltale sign of Angelman syndrome.

The actual number of cases of Angelman syndrome is unknown. Some estimate that one in fifteen thousand babies have Angelman syndrome. Others consider the disorder less prevalent, estimating one in thirty thousand.

Treatment approaches commonly used for Angelman syndrome include behavioral interventions that teach cause and effect relationships, and communication skills. Physical and occupational therapies are used to address erratic movements and posture. Speech therapy is essential and parents are encouraged to participate in the child's treatment program.