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Intellectual development[ edit ] Individuals with FXS may present anywhere on a continuum from learning disabilities in the context of a normal intelligence quotient IQ to severe intellectual disability , with an average IQ of 40 in males who have complete silencing of the FMR1 gene. The main difficulties in individuals with FXS are with working and short-term memory, executive function , visual memory, visual-spatial relationships, and mathematics, with verbal abilities being relatively spared.
However, there is some evidence that standardized IQ decreases over time in the majority of cases, apparently as a result of slowed intellectual development. Social withdrawal behaviors, including avoidance and indifference, appear to be the best predictors of ASD in FXS, with avoidance appearing to be correlated more with social anxiety while indifference was more strongly correlated to severe ASD.
Individuals with FXS show decreased activation in the prefrontal regions of the brain. These children have difficulty in large crowds due to the loud noises and this can lead to tantrums due to hyperarousal.
Hyperactivity and disruptive behavior peak in the preschool years and then gradually decline with age, although inattentive symptoms are generally lifelong. Transitions from one location to another can be difficult for children with FXS. Perseveration is a common communicative and behavioral characteristic in FXS. Children with FXS may repeat a certain ordinary activity over and over. In speech, the trend is not only in repeating the same phrase but also talking about the same subject continually.
Cluttered speech and self-talk are commonly seen. Self-talk includes talking with oneself using different tones and pitches. However, as individuals with FXS generally find these behaviors pleasurable, unlike individuals with OCD, they are more frequently referred to as stereotypic behaviors. Mood symptoms in individuals with FXS rarely meet diagnostic criteria for a major mood disorder as they are typically not of sustained duration. Males with the FMR1 premutation and clinical evidence of FXTAS were found to have increased occurrence of somatization , obsessive—compulsive disorder , interpersonal sensitivity, depression, phobic anxiety, and psychoticism.
This requires early identification to avoid amblyopia. Surgery or patching are usually necessary to treat strabismus if diagnosed early. Refractive errors in patients with FXS are also common. Typically, onset of tremor occurs in the sixth decade of life, with subsequent progression to ataxia loss of coordination and gradual cognitive decline. Phonological memory or verbal working memory deteriorates with age in males, while visual-spatial memory is not found to be directly related to age.
Males often experience an impairment in the functioning of the phonological loop. The CGG length is significantly correlated with central executive and the visual—spatial memory.
However, in a premutation individual, CGG length is only significantly correlated with the central executive, not with either phonological memory or visual—spatial memory. Women with FXPOI can still get pregnant in some cases because their ovaries occasionally release viable eggs. Incidence of the disorder itself is about 1 in every males and 1 in — females. This methylation of FMR1 in chromosome band Xq Before the FMR1 gene was discovered, analysis of pedigrees showed the presence of male carriers who were asymptomatic, with their grandchildren affected by the condition at a higher rate than their siblings suggesting that genetic anticipation was occurring.
Repeat expansion is considered to be a consequence of strand slippage either during DNA replication or DNA repair synthesis. Most of these mRNA targets have been found to be located in the dendrites of neurons, and brain tissue from humans with FXS and mouse models shows abnormal dendritic spines , which are required to increase contact with other neurons. The subsequent abnormalities in the formation and function of synapses and development of neural circuits result in impaired neuroplasticity , an integral part of memory and learning.
FMRP also appears to affect dopamine pathways in the prefrontal cortex which is believed to result in the attention deficit, hyperactivity and impulse control problems associated with FXS. Diagnosis[ edit ] Cytogenetic analysis for fragile X syndrome was first available in the late s when diagnosis of the syndrome and carrier status could be determined by culturing cells in a folate deficient medium and then assessing for " fragile sites " discontinuity of staining in the region of the trinucleotide repeat on the long arm of the X chromosome.
Since the s, more sensitive molecular techniques have been used to determine carrier status. Because this method only tests for expansion of the CGG repeat, individuals with FXS due to missense mutations or deletions involving FMR1 will not be diagnosed using this test and should therefore undergo sequencing of the FMR1 gene if there is clinical suspicion of FXS.
Prenatal testing with chorionic villus sampling or amniocentesis allows diagnosis of FMR1 mutation while the fetus is in utero and appears to be reliable. Most parents notice delays in speech and language skills, difficulties in social and emotional domains as well as sensitivity levels in certain situations with their children. Persons with fragile X syndrome in their family histories are advised to seek genetic counseling to assess the likelihood of having children who are affected, and how severe any impairments may be in affected descendants.
If an individual is diagnosed with FXS, genetic counseling for testing family members at risk for carrying the full mutation or premutation is a critical first-step.
Due to a higher prevalence of FXS in boys, the most commonly used medications are stimulants that target hyperactivity, impulsivity, and attentional problems. Following antidepressants, antipsychotics such as risperidone and quetiapine are used to treat high rates of self-injurious, aggressive and aberrant behaviors in this population Bailey Jr et al.
Drugs targeting the mGluR5 metabotropic glutamate receptors that are linked with synaptic plasticity are especially beneficial for targeted symptoms of FXS. Few studies suggested using folic acid, but more researches are needed due to the low quality of that evidence. However, as there has been very little research done in this specific population, the evidence to support the use of these medications in individuals with FXS is poor.
However, monitoring is required for metabolic side effects including weight gain and diabetes, as well as movement disorders related to extrapyramidal side effects such as tardive dyskinesia. Individuals with coexisting seizure disorder may require treatment with anticonvulsants. Prognosis[ edit ] A review stated that life expectancy for FXS was 12 years lower than the general population and that the causes of death were similar to those found for the general population.
Evidence from mouse models shows that mGluR5 antagonists blockers can rescue dendritic spine abnormalities and seizures, as well as cognitive and behavioral problems, and may show promise in the treatment of FXS.
An open trial in humans has shown promising results, although there is currently no evidence from controlled trials to support its use. And, in , Felix F.
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