The most common symptoms of Williams syndrome are mental disability, heart defects, and unusual facial features. Other symptoms include failure to gain weight appropriately in infancy and low muscle tone.
Most individuals with Williams syndrome are highly verbal and overly sociable, having what has been described as a "cocktail party" type personality, and exhibit a remarkable blend of cognitive strengths and weaknesses. Individuals with WS hyperfocus on the eyes of others in social engagements. Patients tend to have widely spaced teeth, a long philtrum, and flattened nasal bridge.
Individuals with Williams syndrome also experience many cardiac problems, commonly heart murmurs and the narrowing of major blood vessels as well as supravalvular aortic stenosis. Other symptoms may include gastrointestinal problems, such as severe or prolonged colic, abdominal pain and diverticulitis, nocturnal enuresis (bed wetting) and urinary difficulties, dental irregularities and defective tooth enamel, as well as hormone problems, the most common being hypercalcemia (elevated calcium levels in the blood).
Hypothyroidism has been reported to occur in children, although there is no proof of it occurring in adults; diabetes has been reported to occur in adults with WS as young as 21 years old.
Individuals with Williams syndrome often have hyperacusis and phonophobia which resembles noise-induced hearing loss, but this may be due to a malfunctioning auditory nerve. However, individuals with WS can also tend to demonstrate a love of music, and appear significantly more likely to possess perfect pitch.
There also appears to be a higher prevalence of left-handedness and left-eye dominance. Individuals with Williams syndrome also report higher anxiety levels as well as phobia development, which may be associated with hyperacusis.
Furthermore, individuals with Williams syndrome have problems with visual processing, but this is related to difficulty in dealing with complex spatial relationships rather than to issues with depth perception.
In an experiment, a group of children with Williams syndrome showed no signs of inherent racial bias, unlike children without the syndrome.
While patients with Williams syndrome often have abnormal proficiency in verbal skills, they do not perform better on verbal tasks than average. This syndrome is characterized more by a deficiency in other areas of processing. Williams syndrome is notable in that respect in that it represents a double dissociation between verbal and spatial processing.
Williams patients can be highly verbal. When children with Williams syndrome are asked to name an array of animals, they may well list such a wild assortment of creatures as a koala, saber-toothed tiger, vulture, unicorn, sea lion, yak, ibex and "Brontosaurus rex".
Some cultural historians believe that the adjective "elfin" came to be used to describe the facial features of people with Williams syndrome because, before Williams Syndrome's scientific cause was understood, people believed that sufferers of the syndrome, who have very charming and extraordinarily kind personalities in comparison to most people, were gifted with extraordinary, even magical, powers.
This is often believed to be the origin of the folklore of elves, fairies and other forms of the 'good people' or 'wee folk' present in English folklore. Even though they are often described in the literature as "elfin-faced", Steven Pinker says in The Language Instinct that to him they often appearc more like Mick Jagger".
Because of the multiple genes that are missing in people with Williams syndrome, there are many effects on the brain, including abnormalities in the cerebellum, right parietal cortex, and left frontal cortical regions. This pattern is consistent with the visual-spatial disabilities and problems with behavioral timing often seen in Williams syndrome.
Frontal-cerebellar pathways are involved in behavioral timing, and the parietal-dorsal areas of the neocortex handle visual processing that supports visual-spatial analysis of the environment (but not faces). People with Williams syndrome are often affable and hyperverbal – often blurting – which demonstrates the decreased inhibition ability that stems from dorsal-frontal deficits.
There have also been studies that show that the amygdala of a person with Williams syndrome has greater volume than the average person's, and given that the amygdala controls a human's sense of fear, it can be seen why WS individuals can so willingly talk to anyone, including strangers.
Studies in 2010 showed an increased volume and activation of the left auditory cortex in people with Williams Syndrome, which has been interpreted as a neural correlate of their rhythm propensity and fondness of music. Similar sizes of the auditory cortex have been previously reported only in professional musicians.