Oct 3, 2026·Special Population & Related Conditions
Williams Syndrome and IQ: The Typical Range and the Real Cognitive Profile
Williams syndrome IQ scores usually fall in the borderline to moderate intellectual disability range, averaging near 65, with spatial skills weakest.
Dr. Russell T. WarneChief Scientist
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Most people with Williams syndrome have IQ scores in the borderline to moderate intellectual disability range, and in a large, well-documented sample of children the average was about 65. The full-scale score hides a very uneven profile, with spatial construction well below the other main ability clusters and concrete vocabulary well above the overall level.
Williams syndrome is famous for a "verbal strength, spatial weakness" profile, and for an unusually sociable personality and a love of music. Some of that reputation holds up and some of it was overstated. This page covers the typical IQ range, the cognitive profile and how the language strength was revised, why the choice of test changes the picture, how stable scores are with age, and what the research says about sociability and music. The diagnostic criteria for intellectual disability are explained in our article on low IQ and intellectual disability and are not repeated here.
The typical Williams syndrome IQ range
Williams syndrome is caused by the deletion of a small stretch of chromosome 7 (the 7q11.23 region) containing 25 to 27 genes, according to MedlinePlus Genetics. A Norwegian population study by Strømme, Bjørnstad and Ramstad estimated a prevalence of about 1 in 7,500, and MedlinePlus gives a range of 1 in 7,500 to 18,000.
Carolyn Mervis and Angela John reviewed the intellectual profile in 2010 and described a range "from the rare individual in the average range for the general population through the equally rare individual in the severe intellectual disability range," with most people in the borderline to moderate intellectual disability range. In their sample of 120 children and adolescents aged 4 to 17, tested on the Differential Ability Scales, Second Edition (DAS-II), the mean General Conceptual Ability score (similar to a full-scale IQ) was 64.6, with a standard deviation of 12.3 and a range of 31 to 96.
On the usual IQ scale, where the population mean is 100 and the "standard deviation" (the typical distance of a score from the mean) is 15, a score of 65 sits a little more than two standard deviations below average.
The cognitive profile: strong vocabulary, weak spatial construction
The total score averages over abilities that Williams syndrome affects very differently. In the Mervis and John sample, the DAS-II cluster means were 74.1 for verbal ability, 78.9 for nonverbal reasoning and 54.8 for spatial ability. Spatial ability here means "visuospatial construction," the skill of copying a design by assembling its parts, as in drawing or pattern building. At the individual level, 86% of the children scored significantly better on the verbal or the nonverbal reasoning cluster than on the spatial cluster. Our article on visual-spatial reasoning explains what these tasks measure in the general population.
Mervis and colleagues turned this pattern into a formal Williams Syndrome Cognitive Profile in 2000. In 84 people with the syndrome, 74 fit the profile, against only 4 people in a contrast group, and the profile did not vary much with age or overall ability.
The pattern runs roughly opposite to the one in our article on IQ and Down syndrome, where Grieco and colleagues describe nonverbal learning and memory as relative strengths and verbal skills, especially expressive language, as the weaker side.
How the verbal strength was overstated
In 1988, as Mervis and John recount, Bellugi and colleagues described adolescents with Williams syndrome as having excellent language despite severe intellectual disability, and popular articles repeated the idea of "near-normal" language. Jon Brock's 2007 critical review of the language research found "little evidence that syntax, morphology, phonology, or pragmatics are any better than predicted by nonverbal ability." The one consistent exception was receptive vocabulary.
Mervis and John's data make the same point with numbers. Mean scores on the Peabody Picture Vocabulary Test (concrete vocabulary) were about 82, the highest of any measure, and 83% of the children scored at least 70. Relational vocabulary, meaning words for spatial, temporal, quantitative and dimensional concepts such as "behind" or "before," was about 30 points lower than concrete vocabulary in 5- to 7-year-olds. Grammar was at about the level expected for overall ability, and the social use of language was a weakness. The fluent, friendly speech that impressed early observers rests on a narrower set of strengths than the phrase "good language" implies.
Why the test you use changes the picture
The Wechsler editions used in most of this research put nonverbal reasoning and spatial tasks into a single performance composite. Mervis and John point out that on those tests the verbal composite averages only about 5 points higher than the performance composite in Williams syndrome, and in the study by Searcy and colleagues they cite, only 24% of individuals showed a significant verbal advantage. Because the reasoning strength and the spatial weakness are averaged inside one composite, Mervis and John conclude that for most people the Wechsler pattern does not mirror the syndrome's profile. The DAS-II separates the two and is normed down to four standard deviations below the mean, so fewer children hit the bottom of the scale.
Scores are fairly steady over time. Mervis, Kistler, John and Morris tested 40 children four to seven times over an average of about five years and found that mean Kaufman Brief Intelligence Test scores were stable from age 4 to 17, though individual children differed in their trajectories. In a later study of 76 children retested about three years apart, Mervis and Pitts found that mean DAS-II GCA barely moved, and only 11% of children showed a significant individual change, 7% downward and 4% upward. Fisher, Lense and Dykens followed 52 adolescents and adults for up to seven assessments and found that IQ scores were generally stable into adulthood, with significant variability between individuals.
Hypersociability, anxiety and music
The social side of the syndrome is well documented. Jones and colleagues described a "hypersocial" profile, an overfriendly and engaging personality, consistently across infants, toddlers, school-age children and adults. That sociability coexists with high rates of anxiety and attention problems. In a study by Leyfer and colleagues summarized by Mervis and John, 57% of 119 children met criteria for at least one anxiety disorder, most often a specific phobia, and 65% met criteria for ADHD.
Claims about music need the most care. A systematic review of 31 studies by Thakur and colleagues concluded that people with Williams syndrome show a high degree of variability and have musical skills "more in line with their cognitive abilities than chronological age." The review places their musical strengths in interest and emotional responsiveness more than in formal skill. In a sample of 73 adolescents and adults, Lense, Shivers and Dykens found that 11% met criteria for amusia, an impairment in perceiving musical pitch and melody, compared with about 4% in the general population. Enjoying music and being unusually skilled at it are separate questions, and the evidence supports the first more than the second.
Frequently asked questions
What is the average IQ of a person with Williams syndrome?
In a large, detailed sample of children, the mean overall score was about 65, and most people fall in the borderline to moderate intellectual disability range. Rare individuals score in the average range.
Is verbal IQ higher than nonverbal IQ in Williams syndrome?
Often slightly, by about 5 points on Wechsler tests, but the bigger gap is between spatial construction and everything else. Concrete vocabulary and nonverbal reasoning are usually well above spatial skills, while grammar is generally at the level expected from overall ability.
Do IQ scores decline in Williams syndrome?
On average they are fairly stable through childhood and into adulthood, although individual scores do move.
Are people with Williams syndrome musically gifted?
Most show strong interest in music and emotional responsiveness to it, but measured musical skill usually matches overall cognitive ability, and some have difficulty perceiving pitch.
Who should evaluate a person with Williams syndrome?
A psychologist experienced with genetic syndromes, using a test that reports spatial and nonverbal reasoning abilities separately, alongside the person's medical team.
The takeaway
The typical Williams syndrome IQ falls in the borderline to moderate intellectual disability range, with an average in the mid-60s in the best-documented samples. The overall number conceals a sharp spatial weakness and relative strengths in concrete vocabulary and nonverbal reasoning, while the famous language strength turns out to be narrower than early reports suggested. Scores are fairly stable over time, and tests that separate reasoning from spatial construction describe the profile far better than tests that merge them. If you are curious how standard scores and index profiles are built in the general population, an online IQ test built by psychometricians reports the same kind of scale used in these studies.
References
1. MedlinePlus Genetics. (2022). Williams syndrome. National Library of Medicine. medlineplus.gov
2. Strømme, P., Bjørnstad, P. G., & Ramstad, K. (2002). Prevalence estimation of Williams syndrome. Journal of Child Neurology, 17(4), 269-271. doi.org
3. Mervis, C. B., & John, A. E. (2010). Cognitive and behavioral characteristics of children with Williams syndrome: Implications for intervention approaches. American Journal of Medical Genetics Part C: Seminars in Medical Genetics, 154C(2), 229-248. doi.org
4. Mervis, C. B., Robinson, B. F., Bertrand, J., Morris, C. A., Klein-Tasman, B. P., & Armstrong, S. C. (2000). The Williams syndrome cognitive profile. Brain and Cognition, 44(3), 604-628. doi.org
5. Grieco, J., Pulsifer, M., Seligsohn, K., Skotko, B., & Schwartz, A. (2015). Down syndrome: Cognitive and behavioral functioning across the lifespan. American Journal of Medical Genetics Part C: Seminars in Medical Genetics, 169(2), 135-149. doi.org
6. Brock, J. (2007). Language abilities in Williams syndrome: A critical review. Development and Psychopathology, 19(1), 97-127. doi.org
7. Mervis, C. B., Kistler, D. J., John, A. E., & Morris, C. A. (2012). Longitudinal assessment of intellectual abilities of children with Williams syndrome: Multilevel modeling of performance on the Kaufman Brief Intelligence Test-Second Edition. American Journal on Intellectual and Developmental Disabilities, 117(2), 134-155. doi.org
8. Mervis, C. B., & Pitts, C. H. (2015). Children with Williams syndrome: Developmental trajectories for intellectual abilities, vocabulary abilities, and adaptive behavior. American Journal of Medical Genetics Part C: Seminars in Medical Genetics, 169(2), 158-171. doi.org
9. Fisher, M. H., Lense, M. D., & Dykens, E. M. (2016). Longitudinal trajectories of intellectual and adaptive functioning in adolescents and adults with Williams syndrome. Journal of Intellectual Disability Research, 60(10), 920-932. doi.org
10. Jones, W., Bellugi, U., Lai, Z., Chiles, M., Reilly, J., Lincoln, A., & Adolphs, R. (2000). II. Hypersociability in Williams syndrome. Journal of Cognitive Neuroscience, 12(Suppl. 1), 30-46. doi.org
11. Thakur, D., Martens, M. A., Smith, D. S., & Roth, E. (2018). Williams syndrome and music: A systematic integrative review. Frontiers in Psychology, 9, 2203. doi.org
12. Lense, M. D., Shivers, C. M., & Dykens, E. M. (2013). (A)musicality in Williams syndrome: Examining relationships among auditory perception, musical skill, and emotional responsiveness to music. Frontiers in Psychology, 4, 525. doi.org
Hero image: Incomplete gradient pink and blue jigsaw, by Corinne Mildiner, licensed CC BY-SA 4.0 (creativecommons.org/licenses/by-sa/4.0). Via Wikimedia Commons.
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