From MedlinePlus Genetics
Fragile XE syndrome is a genetic disorder that impairs thinking ability and cognitive functioning. Most affected individuals have mild intellectual disabilities. In some people with this condition, cognitive function is described as borderline, which means that it is below average but not low enough to be classified as an intellectual disability. Individuals with two X chromosomes (typical for females) are rarely diagnosed with fragile XE syndrome, likely because the signs and symptoms are so mild, if present at all.

Learning disabilities are the most common sign of impaired cognitive function in people with fragile XE syndrome. The learning disabilities are likely a result of communication and behavioral problems, including delayed speech, poor writing skills, hyperactivity, and a short attention span. Some affected individuals display autistic behaviors, such as hand flapping, repetitive behaviors, and intense interest in a particular subject. Unlike some other forms of intellectual disability, cognitive functioning remains steady and does not decline with age in fragile XE syndrome.  https://medlineplus.gov/genetics/condition/fragile-xe-syndrome