What is Williams Syndrome?

Definition

Williams syndrome is a genetic disorder caused by a deletion of a series of genes on chromosome 7q11. Individuals with Williams syndrome have distinctive facial features, a range of learning difficulties, heart and blood vessel problems, short stature, unique personality traits and distinct learning abilities and deficits.

Description

Williams syndrome, also known as Williams Beuren syndrome, was first described in 1961 by Dr. J.C.P. Williams of New Zealand. At that time it was noted that individuals with Williams Syndrome had an unusual constellation of physical and mental findings. The physical features included a characteristic facial appearance, heart and cardiovascular problems, high blood calcium levels, low birth weight, short stature, and other connective tissue abnormalities. The intellectual problems associated with Williams include a range of learning difficulties and a specific cognitive profile. That is, individuals with Williams Syndrome often have the same pattern of learning abilities and disabilities, as well as many similar personality traits.

The findings in Williams Syndrome are variable, that is, not all individuals with Williams Syndrome will have all of the described findings. In addition to being variable, the physical and mental findings associated with Williams Syndrome are progressive, they change over time.

The genetic profile of Williams Syndrome is a genetic disorder due to a deletion of chromosome material on the long arm of chromosome 7. A series of genes are located in this region. Individuals with Williams Syndrome may have some or all of these genes deleted. Because of this, Williams syndrome is referred to as a contiguous gene deletion syndrome. Contiguous refers to the fact that these genes are arranged next to each other. The size of the deletion can be large or small, which may explain why some individuals with Williams Syndrome are more severely affected than others. If you think of these genes as the letters of the alphabet, some individuals with Williams Syndrome are missing A to M, some are missing G to Q and others are missing A to R. Whilst there are differences in the amount of genetic material that can be deleted, there is a region of overlap. Everyone in the above example was missing G to M. It is thought that the missing genes in this region are important causes of the physical and mental findings of Williams Syndrome.

Two genes in particular, ELN and LIMK1, have been shown to be important in causing some of the characteristic symptoms of Williams Syndrome. The ELN gene codes are for a protein called elastin. The job of elastin in the human body is to provide elasticity to the connective tissues such as those in the arteries, joints, and tendons.

The exact role of the LIMK1 gene is not known. The gene codes are for a substance known as lim kinase 1 that is active in the brain. It is thought that the deletion of the LIMK1 gene may be responsible for the visuospatial learning difficulties of individuals with Williams Syndrome. Many other genes are known to be in the deleted region of chromosome 7q11 responsible for Williams Syndrome and much work is being done to determine the role of these genes in Williams Syndrome.

Williams Syndrome is an autosomal dominant disorder. Genes always come in pairs and in an autosomal dominant disorder, only one gene need be missing or altered for an individual to have the disorder. Although Williams Syndrome is an autosomal disorder, most individuals with Williams Syndrome are the only people in their family with this disorder. When this is the case, the chromosome deletion that causes Williams Syndrome is called de novo. A de novo deletion is one that occurs for the first time in the affected individual. The cause of de novo chromosome deletions is unknown.

Parents of an individual with Williams Syndrome due to a de novo deletion are very unlikely to have a second child with Williams Syndrome. However, once an individual has a chromosome deletion, there is a 50% chance that he or she will pass it on to their offspring. Thus individuals with Williams Syndrome have a 50% chance of passing this deletion (and Williams Syndrome) to their children.

Demographics show that Williams Syndrome occurs in approximately 1 in 20,000 births. Because Williams Syndrome is an autosomal dominant disorder, it affects an equal number of males and females. It is thought that Williams Syndrome occurs in people of all ethnic backgrounds equally.

Signs and symptoms of Williams Syndrome is a multi-system disorder. In addition to distinct facial features, individuals with Williams Syndrome can have cardiovascular, growth, joint, and other physical problems. They also share unique personality traits and have intellectual differences.

Infants with Williams Syndrome are often born small for their family and 70% are diagnosed with failure to thrive during infancy. These growth problems continue throughout the life of a person with Williams Syndrome and most individuals with Williams Syndrome have short stature (height below the third percentile).

Infants with William Syndrome can also be extremely irritable and have “colic-like” behaviour. This behaviour is thought to be due to excess calcium in the blood (hypercalcemia). Other problems that can occur in the first years include strabismus (crossed eyes), ear infections, chronic constipation and eating problems.

Individuals with Williams Syndrome can have distinct facial features sometimes described as “elfin” or “pixie-like.” While none of these individual facial features are abnormal, the combination of the different features is common to Williams Syndrome. Individuals with Williams Syndrome have a small upturned nose, small chin, long upper lip with a wide mouth, small widely spaced teeth and puffiness around the eyes. As an individual gets older, these facial features become more pronounced.

People with Williams Syndrome often have problems with narrowing of their heart and blood vessels. This is thought to be due to the deletion of the elastin gene and is called elastin arteriopathy. Any artery in the body can be affected, but the most common narrowing is seen in the aorta of the heart. This condition is called supravalvar aortic stenosis (SVAS) and occurs in approximately 75% of individuals with Williams Syndrome.

The degree of narrowing is variable. If left untreated, it can lead to high blood pressure, heart disease and heart failure. The blood vessels that lead to the kidney and other organs can also be affected. Deletions of the elastin gene are also thought to be responsible for the loose joints of some children with Williams Syndrome. As individuals with Williams Syndrome age, their heel cords and hamstrings tend to tighten, which can lead to a stiff awkward gait and curving of the spine. Approximately 75% of individuals with Williams Syndrome have mild mental retardation. They also have a unique cognitive profile (unique learning abilities and disabilities). This cognitive profile is independent of their IQ. Individuals with Williams Syndrome generally have excellent language and memorisation skills. They can have extensive vocabularies and may develop a thorough knowledge of a topic that they are interested in. Many individuals are also gifted musicians. Individuals with Williams Syndrome have trouble with concepts that rely on visuospatial ability. Because of this, many people with Williams Syndrome have trouble with maths, writing and drawing. People with Williams Syndrome also often share personality characteristics. They are noted to be very talkative and friendly, sometimes inappropriately and they can be hyperactive. Another shared personality trait is a generalised anxiety

Diagnosis

The diagnosis of Williams Syndrome is usually made by a physician familiar with Williams Syndrome and based upon a physical examination of the individual and a review of his or her medical history. It is often made in infants after a heart problem (usually SVAS) is diagnosed. In children without significant heart problems, the diagnosis may be made after enrolment in school when they are noted to be “slow learners.” While a diagnosis can be made based upon physical examination and medical history, the diagnosis can now be confirmed by a DNA test.

Williams Syndrome is caused by a deletion of genetic material from the long arm of chromosome 7. A specific technique called fluorescent in situ hybridisation testing, or FISH testing, can determine whether there is genetic material missing. A FISH test will be positive (detect a deletion) in over 99% of individuals with Williams Syndrome. A negative FISH test for Williams Syndrome means that no genetic material is missing from the critical region on chromosome 7q11.

Prenatal testing (testing during pregnancy) for Williams Syndrome is possible using the FISH test on DNA sample obtained by chorionic villus sampling (CVS) or by amniocentesis. Chorionic villus sampling is a prenatal test that is usually done between 10 and 12 weeks of pregnancy and involves removing a small amount of tissue from the placenta. Amniocentesis is a prenatal test that is usually performed at 16-18 weeks of pregnancy and involves removing a small amount of the amniotic fluid that surrounds the foetus. DNA is obtained from these samples and tested to see if the deletion responsible for Williams Syndrome is present. While prenatal testing is possible, it is not routinely performed. Typically, the test is only done if there is a family history of Williams Syndrome.

Treatment and management

As Williams Syndrome is a multi-system disorder, the expertise of a number of specialists is required for management of this disorder. The height and growth of individuals with Williams Syndrome should be monitored using special growth curves developed specifically for individuals with Williams Syndrome. Individuals who fall off these growth curves should be assessed for possible eating or thyroid disorders. A cardiologist should evaluate individuals with Williams Syndrome yearly. This examination should include measurement of blood pressure in all four limbs and an echocardiogram of the heart. An echocardiogram is a special form of ultrasound that looks at the structure of the heart. Doppler flow studies, which look at how the blood flows into and out of the heart, should also be done. Individuals with supravalvar stenosis may require surgery to fix this condition. The high blood pressure caused by this condition may be treated with medication. Examinations should take place yearly as some of these conditions are progressive and may worsen over time.

Individuals with Williams Syndrome should also have a complete neurological examination. In addition, the blood calcium levels of individuals with Williams Syndrome should be monitored every two years. High levels of calcium can cause irritability, vomiting, constipations and muscle cramps. An individual found to have a high level of calcium should consult a nutritionist to make sure that their intake of calcium is not higher than 100% of the recommended daily allowance (RDA). Vitamin D can increase calcium levels in individuals with Williams Syndrome and therefore should not take multivitamins containing vitamin D. If calcium levels remain high after limiting vitamin D and decreasing dietary intake of calcium, an individual with hypercalcemia should see a nephrologist for further management and to monitor kidney function.

Strabismus (crossed eyes) can be treated by patching or by surgery. Ear infections can be treated with antibiotics and surgical placement of ear tubes.

The developmental differences of individuals with Williams Syndrome should be treated with early intervention and special education classes. Specific learning strategies that capitalise on the strengths of individuals with Williams Syndrome should be used. Physical, occupational, and speech therapy should be provided. Behavioural counselling and medication may help with behavioural problems such as hyperactivity and anxiety

Prognosis

The prognosis for individuals with Williams Syndrome is highly dependent on the medical complications of a particular individual. Individuals with Williams Syndrome who have no heart complications or very minor ones, have a good prognosis. Good medical care and treatment of potential problems allows most individuals with Williams Syndrome to lead a long life.

The prognosis for individuals with more serious medical complications such as severe heart disease or hypertension is more guarded. Since the medical conditions associated with Williams Syndrome are progressive rather than static, it is very important that individuals with Williams Syndrome have yearly medical examinations with a health care provider familiar with Williams Syndrome. The range of abilities among individuals with Williams Syndrome is very wide and the ultimate functioning of an individual is dependent on his or her abilities.

Whist individuals with Williams Syndrome do well in structured environments such as school, their unique abilities and disabilities do not permit them to do as well in unstructured surroundings. Some individuals with Williams Syndrome live independently but most live with their parents or in a supervised setting. Many individuals with Williams Syndrome can gain employment in supervised settings and do well at tasks that do not require mathematics or visuospatial abilities. It is important to encourage individuals with Williams Syndrome towards independence but to recognise that their friendly and outgoing personalities may lead them into abusive situations.

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Information provided by Kathleen Fergus MS, CGCThe Gale Group Inc., Gale Encyclopaedia of Genetic Disorders Part I, 2002.