What is Williams syndrome?
Williams syndrome is a rare genetic disorder that affects a child's growth, physical appearance, and cognitive development. People who have Williams syndrome are missing genetic material from chromosome 7, including the gene elastin. This gene's protein product gives blood vessels the stretchiness and strength required to withstand a lifetime of use. The elastin protein is made only during embryonic development and childhood, when blood vessels are formed. Because they lack the elastin protein, people with Williams Syndrome have disorders of the circulatory system and heart.
How do people get Williams syndrome?
A deletion is caused by a break in the DNA molecule that makes up a chromosome. In most cases, the chromosome break occurs while the sperm or egg cell (the male or female gamete) is developing. When this gamete is fertilized, the child will develop Williams syndrome. The parent, however, does not have the break in any other cells and does not have the syndrome. In fact, the break is usually such a rare event that it is very unlikely to happen again if the parent has another child.
It is possible for a child to inherit a broken chromosome from a parent who has the disorder. But this is rare because most people with Williams syndrome do not have children.
What are the symptoms of Williams syndrome?
The most common symptoms of Williams syndrome are intellectual disability, heart defects, and unusual facial features (small upturned nose, wide mouth, full lips, small chin, widely spaced teeth).
Other symptoms include low birth weight, failure to gain weight appropriately, kidney abnormalities, and low muscle tone.
People with this syndrome also exhibit characteristic behaviors, such as hypersensitivity to loud noises and an outgoing personality.
How do doctors diagnose Williams syndrome?
Doctors can identify the syndrome by its distinctive physical characteristics. They can confirm the diagnosis by using a special technique called FISH (fluorescent in situ hybridization).
The chromosomal deletion that causes Williams Syndrome is so small that it cannot be seen in a karyotype. The deletion can be observed, however, with FISH. This technique allows DNA sequences to be labeled with a fluorescent chemical (called a probe) that lights up when exposed to ultraviolet (UV) light. The Williams Syndrome deletion can be detected by labeling the elastin gene with a fluorescent probe. The gene will light up under a UV light only if it is present; a lack of signal indicates a deletion.
How is Williams syndrome treated?
There is no cure for Williams syndrome. Patients must be continually monitored and treated for symptoms throughout their lives.
Interesting facts about Williams syndrome
One out of every 10,000 babies is born with Williams syndrome.
Williams syndrome is considered a microdeletion syndrome, because the deletion is too small to be seen with a microscope (fewer than 5 million bases of DNA are deleted).
Deletions that happen during egg and sperm formation are caused by unequal recombination. Recombination normally occurs between pairs of chromosomes during meiosis. If the pairs of chromosomes don't line up correctly, or if the chromosome breaks aren't repaired properly, the structure of the chromosome can be altered. Unequal recombination occurs more often than usual at this location on chromosome 7, likely due to some highly repetitive DNA sequence that flanks the commonly deleted region.