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Fragile X Syndrome
Aka: Fragile X Syndrome, Fragile X Mental Retardation 1 Gene, FMR1, Premutation in FMR1
- Epidemiology
- Most common inherited Developmental Disability
- Full mutation
- Prevalence 1:4000 men and up to 1:6000 women
- Premutation in FMR1 gene carrier
- Prevalence 1:800 men and up to 1:100 women
- Diagnosis often not made until age 8
- Delayed diagnosis due to subtle features
- Pathophysiology
- Fragile X Mutation (FMR1) Gene is on X Chromosome
- Expansion mutation in FMR1 Gene
- Occurs with repetitive CCG in FMR1
- Unaffected patients have <50 CCG repetitions
- Premutation carriers have 50-200 CCG repetitions
- Full mutation patients have >200 CCG repetitions
- Signs: Subtle Phenotype (milder in women)
- Facial features (onset in early childhood)
- Large prominent ears
- Long face or Macrocephaly
- Prominent forehead
- Macroorchidism (after Puberty)
- Mental Retardation (80% of men, 33-65% of women)
- Moderate Mental Retardation (IQ <70)
- Developmental Delay
- Learning Disability
- Abstract reasoning
- Sequential processing
- Mathematics
- Delayed speech
- Males start to talk at 20 months
- Fine and gross motor coordination problems
- Males sit without support at 10 months
- Males start to walk at 20 months
- Behavior problems
- Autistic-like characteristics
- Defensiveness
- Mood instability
- Speech Perseveration
- Anxiety
- Social problems
- Hand flapping
- Hand biting
- Gaze aversion
- Associated conditions
- Epilepsy
- Strabismus
- Connective tissue dysplasia
- Hyperflexible joints
- Mitral Valve Prolapse
- Pes Planus
- Attention Deficit Hyperactivity Disorder
- Affects 80% of fragile X patients
- Conditions associated with premutation carriers
- Premature Ovarian Failure (20% of women)
- Fragile X-Associated Tremor-Ataxia Syndrome (FXTAS)
- Affects 30% men aged 50-60 years old
- Resources
- National Fragile X Foundation
- http://www.FragileX.org
- Fragile-X Research Foundation
- http://fraxa.org
- Gene Tests: FRM1-Related Disorders
- http://www.geneclinics.org/profiles/fragilex/
- References
- Wattendorf (2005) Am Fam Physician 72:111-3 [PubMed]
- Visootsak (2005) Clin Pediatr 44:371-81 [PubMed]