Synopsis
Recognise Fragile X syndrome in children and families, request mechanism-appropriate FMR1 testing, distinguish full mutation from premutation implications, assess associated health needs and provide accurate reproductive counselling.
- Consider Fragile X syndrome in unexplained developmental or intellectual disability, autism, prominent anxiety or hyperarousal, especially with suggestive male relatives or premature ovarian insufficiency in the family.
- Physical features such as long face, large ears, joint laxity and post-pubertal macro-orchidism are variable and often subtle in young children; they cannot confirm or exclude diagnosis.
- Use the current NHS broader genomic pathway, now including whole-genome detection of FMR1 expansion; chromosomal microarray remains unable to exclude Fragile X syndrome.
- Distinguish a full mutation causing Fragile X syndrome from a premutation, which has different reproductive and adult health implications and is not simply a mild full mutation.
- Assess hearing, vision, growth, sleep, seizures, attention, anxiety, autism, communication, motor skills and adaptive function rather than using a single global developmental label.
- Management is multidisciplinary and goal-based: communication support, predictable environment, education planning, behavioural formulation, therapy and treatment of specific coexisting conditions.
- Offer clinical genetics review to explain expansion risk through maternal transmission, testing options for relatives and reproductive choices without directing family decisions.
- Use accessible disclosure as the child matures, protect privacy and avoid deterministic predictions about ability or future independence from repeat size alone.
Key red flags
Developmental regression, new focal neurological signs, prolonged seizures or acute loss of skills requires urgent assessment for another neurological disorder rather than attribution to Fragile X syndrome.
A child with severe agitation, reduced sleep and abrupt behavioural change needs assessment for pain, illness, medication effects, abuse or mental-health crisis before behaviour is labelled syndromic.
Syncope, exertional chest pain or sustained palpitations warrants ordinary emergency cardiovascular assessment even when mitral valve prolapse has previously been documented.
A female premutation carrier with neurological symptoms or ovarian dysfunction, or an older male carrier with tremor and ataxia, needs their own specialist assessment rather than care only through the child.
Investigation priorities
Detect the CGG expansion while evaluating other genomic causes of syndromic intellectual disability.
Management branches
Developmental differences coexist with Fragile-X-compatible behaviour, features or family history.
- Document developmental domains, examination, growth, sensory findings and a three-generation pedigree.
- Refer through the eligible NHS broader genomic pathway and ensure FMR1 expansion analysis is included.
- Continue hearing, vision, developmental and safeguarding assessment while the molecular result is pending.