Williams syndrome is a rare genetic condition (estimated to occur in 1/20,000 births) which causes medical and developmental problems. It is present at birth, and affects males and females equally. It can occur in all ethnic groups and has been identified in countries throughout the world.

Characteristic facial appearance - Most young children with Williams syndrome have similar facial features, often recognized only by a trained geneticist or birth defects specialist. These include a small upturned nose, long philtrum (upper lip length), wide mouth, full lips, small chin, and puffiness around the eyes. Facial features become more apparent with age.

Heart and blood vessel problems - The majority of individuals have some type of heart or blood vessel problem. Typically, there is narrowing in the aorta or narrowing in the pulmonary (lungs) arteries. There is an increased risk for development of high blood pressure over time.

Hypocalcaemia (elevated blood calcium levels) - Some young children have high blood calcium levels. It can cause extreme irritability or "colic-like" symptoms. Occasionally, dietary or medical treatment is needed. In most cases, the problem resolves on its own during childhood, but lifelong abnormality in calcium or Vitamin D metabolism may exist..

Low birth-weight/low weight gain - Most have a slightly lower birth-weight than normal. Slow weight gain, especially during the first several years of life. Adult stature is slightly smaller than average.

Feeding problems - Many infants and young children have feeding problems probably due to low muscle tone, severe gag reflex, poor suck/swallow. Feeding difficulties tend to resolve with age. Many infants have an extended period of colic or irritability which lasts from 4 to 10 months of age.

Dental abnormalities - Slightly small, widely spaced teeth are common in children with Williams syndrome. They also may have a variety of abnormalities of occlusion (bite), tooth shape and appearance. Most of these dental changes are readily amenable to orthodontic correction.

Kidney abnormalities - There is a slightly higher risk of kidney problems

Hernias - Inguinal (groin) and umbilical hernias are common.

Hyperacusis - Children often have more sensitive hearing than other children; Certain frequencies or noise levels can be painful an/or startling to the individual. This condition often improves with age.

Musculoskeletal problems - Young children with Williams syndrome often have low muscle tone and joint laxity. As the children get older, joint stiffness (contractures) may develop. Physical therapy is very helpful in improving muscle tone, strength and joint range of motion.

Overly friendly (excessively social) personality - Individuals with Williams syndrome have a very endearing personality. They have a unique strength in their expressive language skills, and are extremely polite. They are typically unafraid of strangers and show a greater interest in contact with adults than with their peers.

Developmental delay, learning disabilities and attention deficit - Most have some degree of intellectual handicap. Young children often experience developmental delays; milestones such as walking, talking and toilet training are often achieved somewhat later than normal. Distractibility is a common problem in mid-childhood, which appears to get better as the children get older.

Older children and adults with Williams syndrome often demonstrate intellectual "strengths and weaknesses." There are some intellectual areas (such as speech, long term memory, and social skills) in which performance is quite strong, while other intellectual areas (such as fine motor and spatial relations) are significantly deficient.