Genetic Causes of Intellectual Disabilities: Williams Syndrome
Williams syndrome is a relative newcomer on the scene of intellectual disabilities (intellectual development disorder, formerly mental retardation), as it was not identified as a distinct condition until 1961. The cause of the disorder is a mutation of chromosome 7; a fragment of chromosome 7 is missing in the individual's genetic make-up. The mutation seems to be random rather than inherited.
Williams syndrome is not nearly as common as Down syndrome; an estimated 1 in 20,000 babies are born with the disorder. The condition has no affiliation with a specific socioeconomic group. It is equally present in males and females and occurs in all races. Though rare, cases of Williams syndrome have been recorded across the globe.
Common facial features among those who have Williams syndrome are subtle but distinct. They include a tiny upturned nose, a wide, full mouth, a small chin, and distended skin around the eyes. Individuals who have light-colored eyes tend to have a white pattern throughout the iris, described as a starburst design. Physical traits include a longer than normal neck, sloping shoulders, and a generally short stature. The spine tends to curve and there is limited mobility in the joints.
The physical and facial features are so subtle that it usually takes a trained eye to spot them. A geneticist or a birth defect specialist is typically the first to recognize the traits. The physical and facial traits are easily recognized as the child grows, however, because of the irregular body proportions that occur.
Certain medical problems tend to accompany Williams syndrome, and may shorten the lifespan of children with this condition. Cardiovascular disease resulting from narrowed arteries is the most daunting medical condition. Stomach problems, including colic in infancy and abdominal pain throughout adolescent and adult years, are also common. Diabetes is another common complication that usually develops by the time a child with this condition reaches the age of 13. Hearing loss, caused by auditory nerve dysfunction, also occurs with frequency in Williams syndrome.
The pattern of developmental delays associated with Williams syndrome is more or less similar to other causes of intellectual disabilities. A varying degree of cognitive impairment and adaptive functioning will be present. Young children with Williams syndrome experience developmental delays in motor skills including walking and toilet training. They also tend to develop speech later than their peers, although expressive language is one of their strengths in later years. Another deficit that improves with age is attention.
After a certain age, individuals with Williams syndrome tend to develop good verbal skills and short-term memory abilities. Despite great verbal fluency (easy use of words and good command of grammar and vocabulary), they tend to think in a concrete manner. Abstract and figurative language such as metaphor remain difficult. There is also a set of spatial deficits that make it difficult to learn to write and draw. The Attention Deficit/Hyperactivity Disorder (ADHD) occurs more frequently in children with Williams syndrome than in the general population.
Typical personality traits are easily recognized in this rare genetic disorder. Children with Williams syndrome tend to be very friendly and lovable. Their endearing, loving qualities are magnified by their proficient and well developed use of language and communication skills. Unfortunately, these same traits also make them vulnerable to victimization. Children with Williams syndrome often show no fear of strangers, and they can be too friendly and empathetic for their own good. Children with Williams syndrome typically prefer the company of adults to peers, and this can become a significant social problem within their peer groups. They may also demonstrate high levels of anxiety during stressful or unfamiliar situations.
Adults with Williams syndrome have varying prospects for independent functioning. Some are able to live independently or in group homes, but most remain with family or require a primary caregiver. Many are able to complete their academic education and to sustain employment.