X-linked dominant genetic disorder Fragile X syndrome Other names Martin–Bell syndrome, [1] Escalante syndrome Boy with protruding ears characteristic of fragile X syndrome Specialty Medical genetics , pediatrics , psychiatry Symptoms Intellectual disability , long and narrow face, large ears, flexible fingers, large testicles [1] Complications Autism features, seizures [1] Usual onset Noticeable by age 2 [1] Duration Lifelong [2] Causes Genetic ( X-linked dominant ) [1] Diagnostic method Genetic testing [2] Treatment Supportive care , early interventions [2] Frequency 1 in 4,000 (males), 1 in 8,000 (females) [1] Fragile X syndrome ( FXS ) is a genetic disorder characterized by mild-to-moderate intellectual disability . [1] The average IQ in males is under 55, while about two thirds of affected females are intellectually disabled. [3] [4] Physical features may include a long and narrow face, large ears, flexible fingers, and large testicles . [1] About a third of those affected have features of autism such as problems with social interactions and delayed speech. [1] Hyperactivity is common, and seizures occur in about 10%. [1] Males are usually more affected than females. [1] This disorder and finding of Fragile X syndrome has an X-linked dominant inheritance. [1] It is typically caused by an expansion of the CGG triplet repeat within the FMR1 (fragile X mental retardation 1) gene on the X chromosome . [1] This results in silencing ( methylation ) of this part of the gene and a deficiency of the resultant protein (FMRP), which is required for the normal development of connections between neurons . [1] Diagnosis requires genetic testing to determine the number of CGG repeats in the FMR1 gene. [5] Normally, there are between 5 and 40 repeats; fragile X syndrome occurs with more than 200. [1] A premutation is said to be present when the gene has between 40 and 200 repeats; women with a premutation have an increased risk of having an affected child. [1] Testing for premutation carriers may allow for genetic counseling . [5] There is no cure. [2] Early intervention is recommended, as it provides the most opportunity for developing a full range of skills. [6] These interventions may include special education , speech therapy , physical therapy , or behavioral therapy . [2] [7] Medications may be used to treat associated seizures , mood problems, aggressive behavior, or ADHD . [8] Fragile X syndrome is estimated to occur in 1.4 per 10,000 males and 0.9 per 10,000 females. [9] Contents 1 Signs and symptoms 1.1 Physical phenotype 1.2 Intellectual development 1.3 Autism 1.4 Social interaction 1.5 Mental health 1.6 Vision 1.7 Neurology 1.8 Working memory 1.9 Fertility 2 Causes 2.1 Inheritance 3 Pathophysiology 4 Diagnosis 5 Management 5.1 Medication 6 Prognosis 7 Research 8 History 9 References 10 External links Signs and symptoms [ edit ] Prominent characteristics of the syndrome include an elongated face and large or protruding ears. Most young children do not show any physical signs of FXS. [10] It is not until puberty that physical features of FXS begin to develop. [10] Aside from intellectual disability, prominent characteristics of the syndrome may include an elongated face, large or protruding ears , flat feet, larger testes ( macroorchidism ), and low muscle tone . [11] [12] Recurrent otitis media (middle ear infection) and sinusitis is common during early childhood. Speech may be cluttered or nervous. Behavioral characteristics may include stereotypic movements (e.g., hand-flapping) and atypical social development, particularly shyness, limited eye contact, memory problems, and difficulty with face encoding. Some individuals with fragile X syndrome also meet the diagnostic criteria for autism . Males with a full mutation display virtually complete penetrance and will therefore almost always display symptoms of FXS, while females with a full mutation generally display a penetrance of about 50% as a result of having a second, normal X chromosome. [13] Females with FXS may have symptoms ranging from mild to severe, although they are generally less affected than males.