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Fragile X syndrome is the leading cause of inherited intellectual disability and is often accompanied by autism. Dozens of fragile X drugs have entered clinical trials in the past decade. But none of them seem to improve cognition in people with the syndrome.
However, the tools typically used to measure cognitive skills are designed for the general population and aren’t sensitive enough to detect subtle improvements in people with severe impairment. They also cannot reliably compare individuals with different diagnoses.
The collection of seven tests, called the National Institutes of Health Toolbox Cognition Battery, was developed in 2013 to capture cognition in people intellectual disability2. But researchers validated the test only in the general population.
The 3- to 10-minute tests tap memory, reading, vocabulary, information-processing speed and executive function, a set of mental skills that includes planning and attention. The tests also cover social skills and ability to perform everyday tasks, such as gathering the supplies needed to assemble an ice cream cone.
In the new study, published 6 September in the Journal of Neurodevelopmental Disorders, researchers tried out the set of tests on 63 people with fragile X, 47 people with Down syndrome and 16 people who have intellectual disability with no known cause. The participants ranged in age from 10 to 27 years, with an average mental age of about 5 years.
The participants took all seven tests over two days. They also took six tests traditionally used to gauge cognitive skills in people with intellectual disability.
Most of the participants scored in the severely impaired range on the traditional tests. They performed similarly on the new set. But because the new set’s rubric includes a wider span of scores at the lower end, it can more finely gauge the degree of impairment.
The new set also allows comparisons across types of intellectual disability. People with fragile X or Down syndrome have more difficulty with tasks requiring attention and inhibitory control than those who have intellectual disability with no known cause, for example. Individuals with fragile X syndrome have the poorest reading skills and those with Down syndrome have the smallest vocabulary.
The researchers plan to assess how well the battery works for tracking cognitive skills over time. If the tests pass that test, scientists could use the new set to uncover subtle improvements in participants in fragile X trials.