Genetic diagnosis

Consider a diagnosis of fragile X syndrome (FXS) for any individual with clinical characteristics or a family history of fragile X syndrome. Diagnosis can only be confirmed with DNA testing. Delayed diagnosis of fragile X syndrome is common because physical characteristics are not always present and developmental delay may only appear mild in young children.

Testing for fragile X syndrome using DNA studies is sensitive and specific. It also reliably detects carriers of the premutation. In children, if fragile X syndrome is suspected, refer to a paediatrician for testing. Ordering chromosome microarray and fragile X syndrome tests in parallel with referral to a paediatrician can reduce waiting times for patients.

In adults, if fragile X syndrome is suspected, consider referral to a clinical geneticist or clinician with expertise in fragile X syndrome for advice about genetic testing and counselling.

The genetic testing request should specify ‘DNA studies for fragile X syndrome’. Medicare rebates may apply; see Medicare Benefits Schedule (MBS) Online. For information on genetic testing, see Genetic testing for developmental disability.

Occasionally, people with other syndromes or disabilities (eg Down syndrome, cerebral palsy, Pierre Robin syndrome, Prader–Willi syndrome) have concomitant fragile X syndrome; if there is reason to suspect this, the person should be tested for fragile X.