Angelman Syndrome is a genetic disorder that causes neurological symptoms, particularly in the central nervous system. These include developmental delays and mental retardation, severe speech impairment, seizures, small head size (microcephaly), and movement and balance problems (ataxia).

Children who have Angelman syndrome typically appear normal at birth. However, they may begin to experience feeding problems at 1 month to 2 months of age and developmental delays usually become apparent between the ages of 6 months and 1 year. Developmental delays include sitting upright after 12 months of age, and not walking until 3 to 5 years of age. Puberty is also delayed in people with Angelman syndrome, typically by one to three years. The condition affects one in 10,000 to 20,000 people, according to the National Institutes of Health (NIH).

Humans have 23 pairs of chromosomes, and each chromosome carries multiple to hundreds of genes. Angelman syndrome is a result of a genetic problem related to chromosome 15. Mutations in the ubiquitin ligase E3A (UBE3A) gene on this chromosome appear to cause Angelman syndrome, although the absence of another gene (called OCA2)  from chromosome 15 is also associated with this syndrome.

Normally, people receive two copies of the UBE3A gene, one from each parent. In the brain, only the copy inherited from the mother is an active gene. When the maternal copy is lost due to a chromosomal change or gene mutation, Angelman syndrome is likely to result. About 70 percent of patients with Angelman syndrome are missing the maternal copy of chromosome 15, according to the NIH.

Other causes of Angelman syndrome include:

• Having two copies of paternal chromosome 15 instead of one from each parent. This occurs in 3 to 7 percent of all cases. Angelman syndrome results because the paternal chromosome is not capable of being active in the brain.
  
  
• Mutation in UBE3A gene. Occurs in 10 percent of cases.
  
  
• Defect in DNA region that controls activation of UBE3A gene. Occurs in about 3 percent of cases.

When the OCA2 gene is also deleted from chromosome 15, a person with Angelman syndrome is likely to have light-colored hair and skin, compared to family members. This occurs because the OCA2 gene controls the protein that produces the pigment melanin, which provides color to hair, skin and eyes.

Most cases of Angelman syndrome occur even though there is no history of the disorder in the patient’s family. The syndrome often is a result of a random genetic mutation that occurs during the formation of cells early in embryonic development. The cause remains unknown in about 10 to 15 percent of Angelman syndrome cases.