The symptoms that are associated with genetic syndromes generally form a large and diverse array of physical and behavioral characteristics. Knowledge about the relationship of these features to each disorder’s genotype varies greatly. The cognitive and behavioral phenotypes of most genetic disorders are typically less well characterized than the physical/medical ones and are less clearly linked to genetic causes.
- The symptoms of Down syndrome vary from person to person, and people with Down syndrome may have different problems at different times of their lives. Cognitive impairment, problems with thinking and learning, is common in people with Down syndrome and usually ranges from mild to moderate. Only rarely is Down syndrome associated with severe cognitive impairment
- In Fragile X syndrome approximately 50% of females with the full mutation have intellectual impairments while the remaining 50% may manifest borderline to normal intellectual functioning, learning disability, and/or psychosocial difficulties. The majority of males with Fragile X syndrome have intellectual impairments.
- Females with Turner syndrome manifest a specific neurocognitive profile where verbal ability is generally normal, while nonverbal ability, attention, working memory, motor function, and executive function (planning, organizing) are relatively impaired.
- Most individuals with Williams Syndrome rank in the mild to moderately intellectually impaired range and no clinically significant difference between Verbal and Nonverbal intelligence scores.
In the chromosome 22q11.2 deletion or Velocardiofacialsyndrome (VCFS), a subset of impairments is particularly evident in the areas of visuospatial and math performance. Despite their early language delays, children with VCFS still score higher on standardized tests of verbal abilities than those that test visuospatial abilities.