Study On Screening, Diagnosis And Social Adaptation Of Children With Fragile X Syndrome And The Neuromechanism Of Fmr1Knockout Mice

Fragile X mental retardation syndrome (hereafter FXS) is one of the most common genetic syndromes causing mental retardation, with an estimated prevalence of1in4000in the population. FXS results from a CGG repeat expansion that triggers hypermethylation and silencing of the FMR1gene. FXS is characterized by moderate to severe mental retardation, pubertal macroorchidism, and facial features, including long face, large and prominent ears. Many individuals with FXS have behavioral problems including impulsion, hyperactivity and autistic behavior, such as anxiety, social withdrawal, stereotyped speech etc. Early diagnosis, early intervention and treatment would improve the prognosis of the patients. The diagnosis of proband would also make it possible that the familial members get genetic counseling from geneticist and avoid future sufferer.In the present study, we developed an assay called "double real time fluorescent quantitative PCR", common real time PCR and methylation-sensitive restriction enzymes-based quantitative PCR (MSRE-QPCR), to quantitatively assess FMR1gene CGG-repeats and the methylation status of CpG islands respectively. This assay displays high specificity and sensitivity for detecting FMR1methylation, successfully distinguishing males with full mutation or full mutation/permutation mosaic FXS from normal males. Females with FMR1full mutations can also be detected by this assay. But it is not sensitive enough to discriminate full mutations female and mosaic female with full mutation and permutation. Furthermore, the assay is inexpensive and can be carried out with high-throughput. So it can be used to screen and diagnose fragile â…© syndrome especially in male population.Thus far, there is no study on clinical features and social adaptation in children with FXS in China. In this study, we carried out the assessments among FXS boys with a clinical checklist and Infants-Junior Middle School Students'Social-Life Abilities Scales. It was found that the simplified six-item checklist for screening for fragile â…© syndrome is suitable for Chinese male children. If a score of5or more is used as the criterion for requesting fragile â…© testing, then61.6%of those tests from our patient population could have been eliminated without missing any positive cases. We also found that the prevalence of attention deficit hyperactivity disorder (ADHD) among our boys with FXS was higher than that of western countries. That might be partially ascribed to fewer medicines taken by our children. As to the social skills, boys with FXS in China developed the same level as that of mental age matched controls from normal and Down syndrome boys, and were more delayed than the chronological age matched controls. Moreover, different domains of social skills were unbalanced in boys with FXS. The domains of operation, socialization and self-direction of boys with FXS were even poorer than that of controls. We need to pay more attention to the early intervention of children with fragile â…© syndrome.Treatments for FXS targeted to the neurobiology mechanisms are developed largely based on work in the Fmr1knockout mouse model. In the present study, we assessed the spatiotemporal expression of postsynaptic density95(PSD-95) and its mRNA in Fmr1knockout mice brain regions (cortex, hippocampus and cerebellum) with real time quantitative reverse transcription PCR, immunohistochemistry and Western blot. It was found that in the three principal brain areas of Fmrl knockout mice and wild-type mice, the expression of PSD-95mRNA and protein were detected in the lowest levels on7th postnatal day (P7), and then significantly increased on P14, reaching the peak levels at adolescent or adult. Moreover, it was found that PSD-95mRNA and protein in hippocampus were significantly decreased in Fmrl knockout mice during developmental period (P7, P14, P21and P28) as well as adult (P90). However, there is no significant difference of expression of PSD-95in cortex and cerebellum between Fmrl knockout and wild mice. The expression of PSD-95in the hippocampus might be regulated by fragile X mental retardation protein (FMRP) during mice early developmental and adult period. It is suggested that impairment of PSD-95was possible involved in hippocampal-dependent learning defects, which are common in people with FXS. So work on treatments for FXS targeted the pathway of PSD-95should be carried out in the future.