Editing Fragile X syndrome (section)

==Diagnosis==
Clinical diagnosis relies on identifying a variant of FMR1 associated with decreased function alongside moderate to severe intellectual impairment, particularly in males or moderate in females. Diagnostic tests include PCR to analyze the number of CGG repeats, Southern blot analysis, and examination of AGG trinucleotides in the FMR1 gene region.

[[Cytogenetic]] analysis for fragile X syndrome was first available in the late 1970s when diagnosis of the syndrome and carrier status could be determined by culturing cells in a folate deficient medium and then assessing for "[[fragile site]]s" (discontinuity of staining in the region of the trinucleotide repeat) on the long arm of the X chromosome.<ref name="Hogan">{{cite journal | vauthors = Hogan AJ | title = Visualizing carrier status: fragile X syndrome and genetic diagnosis since the 1940s | journal = Endeavour | volume = 36 | issue = 2 | pages = 77–84 | date = June 2012 | pmid = 22257912 | doi = 10.1016/j.endeavour.2011.12.002 | url = https://zenodo.org/record/894526 | access-date = 2018-04-20 | url-status = live | archive-url = https://web.archive.org/web/20191105204324/https://zenodo.org/record/894526 | archive-date = 2019-11-05 }}</ref> This technique proved unreliable, however, as the fragile site was often seen in less than 40% of an individual's cells. This was not as much of a problem in males, but in female carriers, where the fragile site could generally only be seen in 10% of cells, the mutation often could not be visualised.{{citation needed|date=August 2021}}

Since the 1990s, more [[Sensitivity and specificity|sensitive]] molecular techniques have been used to determine carrier status.<ref name=Hogan/> The fragile X abnormality is now directly determined by analysis of the number of CGG repeats using [[polymerase chain reaction]] (PCR) and methylation status using [[Southern blot]] analysis.<ref name=Garber/> By determining the number of CGG repeats on the X chromosome, this method allows for more accurate assessment of risk for premutation carriers in terms of their own risk of fragile X associated syndromes, as well as their risk of having affected children. Because this method only tests for expansion of the CGG repeat, individuals with FXS due to [[missense mutations]] or [[Deletion (genetics)|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.{{citation needed|date=September 2021}}

Prenatal testing with [[chorionic villus sampling]] or [[amniocentesis]] allows diagnosis of FMR1 mutation while the fetus is in utero and appears to be reliable.<ref name=Garber/>

Early diagnosis of fragile X syndrome or carrier status is important for providing early intervention in children or fetuses with the syndrome, and allowing genetic counselling with regards to the potential for a couple's future children to be affected. 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.<ref>{{Cite web|url=https://www.nichd.nih.gov/health/topics/fragilex/conditioninfo/Pages/diagnosed.aspx|title=How do health care providers diagnose Fragile X syndrome?|website=  National Institute of Child Health and Human Development |publisher =NIH|location = US | date = 2021-08-25 |access-date=2016-11-21|url-status=live|archive-url=https://web.archive.org/web/20161121234354/https://www.nichd.nih.gov/health/topics/fragilex/conditioninfo/Pages/diagnosed.aspx|archive-date=2016-11-21}}</ref>