Fragile X Syndrome

🧬 Fragile X Syndrome (FXS)

NP Student Educational Guide

✅ Overview

Fragile X Syndrome is the most common inherited cause of intellectual disability and a leading single-gene cause of autism spectrum disorder (ASD).

🧠 It results from a genetic mutation on the X chromosome that affects brain development, behavior, and cognition.

🧬 Genetics & Cause

  • Caused by a mutation in the FMR1 gene on the X chromosome.

  • In normal individuals: FMR1 has <55 CGG triplet repeats.

  • In Fragile X: >200 CGG repeats → this is a full mutation.

This leads to silencing of the FMR1 gene → ↓ production of FMRP protein, which is essential for brain function and synaptic development.

🔹 Inheritance Pattern:

  • X-linked dominant

  • Affects males more severely (only one X chromosome)

  • Females may have milder symptoms due to a second X chromosome

👶 Clinical Features

Neurodevelopmental:

  • Intellectual disability (moderate to severe in males, milder in females)

  • Speech and language delays

  • Autism spectrum behaviors:

    • Poor eye contact

    • Repetitive behaviors

    • Sensory processing issues

Behavioral:

  • Hyperactivity, impulsivity (often misdiagnosed as ADHD)

  • Social anxiety

  • Mood lability

Physical Features (more evident in males):

  • Long, narrow face

  • Prominent ears and jaw

  • High-arched palate

  • Macroorchidism (large testicles, post-puberty)

  • Joint hypermobility

  • Flat feet

Other:

  • Seizures (~15–20%)

  • Sleep disturbances

  • Connective tissue problems (e.g., mitral valve prolapse)

🔍 Diagnosis

1. Genetic Testing (definitive):

  • DNA testing for FMR1 CGG repeat expansion

  • Prenatal testing available for at-risk pregnancies

2. Developmental Screening:

  • Identify delays in speech, motor, or cognitive milestones

  • Consider FXS in children with unexplained intellectual disability or ASD

🛠 Management

There is no cure, but early intervention and supportive therapies are critical.

Multidisciplinary Care:

  • Speech and language therapy

  • Occupational therapy

  • Behavioral therapy (ABA)

  • Special education services (IEPs)

  • Physical therapy for hypotonia or motor delays

Medications (to manage symptoms):

  • Stimulants for ADHD symptoms (e.g., methylphenidate)

  • SSRIs for anxiety/mood

  • Atypical antipsychotics for aggression or severe behavioral issues

🧠 Role of the NP

1. Recognize and Refer:

  • Identify early developmental delays or autism features

  • Consider FXS in boys with intellectual disability and autism

  • Order appropriate genetic testing or refer to genetics

2. Coordinate Care:

  • Connect families to early intervention programs

  • Refer to:

    • Developmental pediatrics

    • Speech/OT/PT

    • Neurology (if seizures present)

    • Genetics and counseling

3. Educate and Support Families:

  • Explain the diagnosis and implications

  • Discuss inheritance patterns and family planning

  • Address psychosocial needs, support groups, and long-term care planning

🧾 Family Considerations

  • Carrier testing for family members, especially females

  • Women with a premutation (55–200 CGG repeats) may be at risk for:

    • FXTAS (Fragile X–associated tremor/ataxia syndrome)

    • FXPOI (Fragile X–associated primary ovarian insufficiency)

📝 Clinical Pearl

If a male child has intellectual disability, social anxiety, speech delays, and physical features like a long face and large ears, think Fragile X Syndrome—especially with a family history of similar traits.