{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,25]],"date-time":"2026-04-25T00:30:04Z","timestamp":1777077004662,"version":"3.51.4"},"reference-count":58,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2016,11,30]],"date-time":"2016-11-30T00:00:00Z","timestamp":1480464000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Genes"],"abstract":"<jats:p>The identification of a trinucleotide (CGG) expansion as the chief mechanism of mutation in Fragile X syndrome in 1991 heralded a new chapter in molecular diagnostic genetics and generated a new perspective on mutational mechanisms in human genetic disease, which rapidly became a central paradigm (\u201cdynamic mutation\u201d) as more and more of the common hereditary neurodevelopmental disorders were ascribed to this novel class of mutation. The progressive expansion of a CGG repeat in the FMR1 gene from \u201cpremutation\u201d to \u201cfull mutation\u201d provided an explanation for the \u201cSherman paradox,\u201d just as similar expansion mechanisms in other genes explained the phenomenon of \u201canticipation\u201d in their pathogenesis. Later, FMR1 premutations were unexpectedly found associated with two other distinct phenotypes: primary ovarian insufficiency and tremor-ataxia syndrome. This review will provide a historical perspective on procedures for testing and reporting of Fragile X syndrome and associated disorders, and the population genetics of FMR1 expansions, including estimates of prevalence and the influence of AGG interspersions on the rate and probability of expansion.<\/jats:p>","DOI":"10.3390\/genes7120110","type":"journal-article","created":{"date-parts":[[2016,11,30]],"date-time":"2016-11-30T10:10:36Z","timestamp":1480500636000},"page":"110","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Development of Genetic Testing for Fragile X Syndrome and Associated Disorders, and Estimates of the Prevalence of FMR1 Expansion Mutations"],"prefix":"10.3390","volume":"7","author":[{"given":"James","family":"Macpherson","sequence":"first","affiliation":[{"name":"Wessex Regional Genetics Laboratory, Salisbury NHS Foundation Trust, Salisbury District Hospital, Salisbury SP2 8BJ, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Anna","family":"Murray","sequence":"additional","affiliation":[{"name":"Medical School, University of Exeter, RILD Level 3, Royal Devon &amp; Exeter Hospital, Barrack Road, Exeter EX2 5DW, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2016,11,30]]},"reference":[{"key":"ref_1","first-page":"9","article-title":"The Fragile (X): A marker for the Martin-Bell syndrome","volume":"3","author":"Jacobs","year":"1985","journal-title":"Dis. Markers"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"396","DOI":"10.1136\/jmg.23.5.396","article-title":"The frequency of the fragile X chromosome among schoolchildren in Coventry","volume":"23","author":"Webb","year":"1986","journal-title":"J. Med. Genet."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1210","DOI":"10.1016\/0140-6736(92)91142-U","article-title":"Population screening for fragile X","volume":"339","author":"Turner","year":"1992","journal-title":"Lancet"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"821","DOI":"10.1016\/S0022-3476(87)80392-X","article-title":"Fragile X syndrome","volume":"110","author":"Chudley","year":"1987","journal-title":"J. Paediatr."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"289","DOI":"10.1007\/BF00291644","article-title":"Further segregation analysis of the fragile X syndrome with special reference to transmitting males","volume":"69","author":"Sherman","year":"1985","journal-title":"Hum. Genet."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"709","DOI":"10.1002\/ajmg.1320210413","article-title":"A premutation that generates a defect at crossing-over explains the inheritance of fragile X mental retardation","volume":"21","author":"Pembrey","year":"1985","journal-title":"Am. J. Med. Genet. Part A"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1097","DOI":"10.1126\/science.252.5009.1097","article-title":"Instability of a 550-base pair DNA segment and abnormal methylation in Fragile X syndrome","volume":"252","author":"Rousseau","year":"1991","journal-title":"Science"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"905","DOI":"10.1016\/0092-8674(91)90397-H","article-title":"Identification of a gene (FMR-1) containing a CGG repeat coincident with a breakpoint cluster region exhibiting length variation in Fragile X syndrome","volume":"65","author":"Verkerk","year":"1991","journal-title":"Cell"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"1711","DOI":"10.1126\/science.1675488","article-title":"Mapping of DNA instability at the Fragile X to a trinucleotide repeat sequence p(CCG)n","volume":"252","author":"Kremer","year":"1991","journal-title":"Science"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"4355","DOI":"10.1093\/nar\/19.16.4355","article-title":"Molecular heterogeneity of the fragile X syndrome","volume":"19","author":"Nakahori","year":"1991","journal-title":"Nucl. Acids Res."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"901","DOI":"10.1093\/hmg\/9.6.901","article-title":"Understanding the molecular basis of fragile X syndrome","volume":"9","author":"Jin","year":"2000","journal-title":"Hum. Mol. Genet."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"3636","DOI":"10.1073\/pnas.92.9.3636","article-title":"Simple tandem repeats and human genetic disease","volume":"92","author":"Sutherland","year":"1995","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1047","DOI":"10.1016\/0092-8674(91)90283-5","article-title":"Variation of the CGG repeat at the Fragile X site results in genetic instability: Resolution of the Sherman paradox","volume":"67","author":"Fu","year":"1991","journal-title":"Cell"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"1673","DOI":"10.1056\/NEJM199112123252401","article-title":"Direct diagnosis by DNA analysis of the Fragile X syndrome of mental retardation","volume":"325","author":"Rousseau","year":"1991","journal-title":"New Eng. J. Med."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"298","DOI":"10.1002\/ajmg.1320510404","article-title":"High functioning Fragile X males: Demonstration of an unmethylated fully expanded FMR-1 mutation associated with protein expression","volume":"51","author":"Hagerman","year":"1994","journal-title":"Am. J. Med. Genet."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"127","DOI":"10.1016\/0092-8674(93)90300-F","article-title":"Trinucleotide repeat amplification and hypermethylation of a CpG island in FRAXE mental retardation","volume":"74","author":"Knight","year":"1993","journal-title":"Cell"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"802","DOI":"10.1136\/jmg.29.11.802","article-title":"Frequent small amplifications in the FMR-1 gene in fra(X) families: Limits to the diagnosis of \u2018premutations\u2019","volume":"29","author":"Macpherson","year":"1992","journal-title":"J. Med. Genet."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"196","DOI":"10.1002\/(SICI)1096-8628(19960712)64:1<196::AID-AJMG35>3.0.CO;2-G","article-title":"Prevalence of Fragile X Syndrome","volume":"64","author":"Turner","year":"1996","journal-title":"Am. J. Med. Genet."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"415","DOI":"10.1136\/jmg.37.6.415","article-title":"FRAXA and FRAXE: The results of a five year survey","volume":"37","author":"Youings","year":"2000","journal-title":"J. Med. Genet."},{"key":"ref_20","first-page":"103","article-title":"Predisposition to the Fragile X Syndrome in Jews of Tunisian descent is due to the absence of AGG interruptions on a rare Mediterranean haplotype","volume":"60","author":"Shachak","year":"1997","journal-title":"Am. J. Hum. Genet."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"226","DOI":"10.1002\/ajmg.10427","article-title":"Prevalence of the fragile X syndrome in African-Americans","volume":"110","author":"Crawford","year":"2002","journal-title":"Am. J. Med. Genet."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"454","DOI":"10.1086\/367713","article-title":"Expansion of the Fragile X CGG repeat in females with premutation or intermediate alleles","volume":"72","author":"Nolin","year":"2003","journal-title":"Am. J. Hum. Genet."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"306","DOI":"10.2353\/jmoldx.2009.080174","article-title":"Expansion of an FMR1 grey-zone allele to a full mutation in two generations","volume":"11","author":"Pan","year":"2009","journal-title":"J. Mol. Diagn."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"173","DOI":"10.1093\/hmg\/6.2.173","article-title":"The role of size, sequence and haplotype in the stability of FRAXA and FRAXE alleles during transmission","volume":"6","author":"Murray","year":"1997","journal-title":"Hum. Mol. Genet."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"88","DOI":"10.1038\/ng0994-88","article-title":"Length of uninterrupted CGG repeats determines instability in the FMR1 gene","volume":"8","author":"Eichler","year":"1994","journal-title":"Nature Genet."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"319","DOI":"10.1093\/hmg\/5.3.319","article-title":"Haplotype and interspersion analysis of the FMR1 CGG repeat identifies two different mutational pathways for the origin of the fragile X syndrome","volume":"5","author":"Eichler","year":"1996","journal-title":"Hum. Mol. Genet."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"1935","DOI":"10.1093\/hmg\/7.12.1935","article-title":"Re-examination of factors associated with expansion of CGG repeats using a single nucleotide polymorphism in FMR1","volume":"7","author":"Gunter","year":"1998","journal-title":"Hum. Mol. Genet."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"99","DOI":"10.1002\/1096-8628(20000717)93:2<99::AID-AJMG4>3.0.CO;2-W","article-title":"Haplotype and AGG-interspersion analysis of FMR1 (CGG)n alleles in the Danish population: Implications for multiple mutational pathways towards Fragile X alleles","volume":"93","author":"Larsen","year":"2000","journal-title":"Am. J. Med. Genet."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"358","DOI":"10.1038\/gim.2014.106","article-title":"Fragile X full mutation expansions are inhibited by one or more AGG interruptions in premutation carriers","volume":"17","author":"Nolin","year":"2015","journal-title":"Genet. Med."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"853","DOI":"10.1016\/0092-8674(94)90134-1","article-title":"Cryptic and polar variation of the Fragile X repeat could result in predisposing normal alleles","volume":"77","author":"Kunst","year":"1994","journal-title":"Cell"},{"key":"ref_31","first-page":"351","article-title":"Fragile X gene instability: Anchoring AGGs and linked microsatellites","volume":"57","author":"Zhong","year":"1995","journal-title":"Am. J. Hum. Genet."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"399","DOI":"10.1093\/hmg\/3.3.399","article-title":"Insert size and flanking haplotype in fragile X and normal populations: Possible multiple origins for the fragile X mutation","volume":"3","author":"Macpherson","year":"1994","journal-title":"Hum. Mol. Genet."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1543","DOI":"10.1093\/hmg\/3.9.1543","article-title":"Sequence analysis of the fragile X trinucleotide repeat: Implications for the origin of the fragile X mutation","volume":"3","author":"Snow","year":"1994","journal-title":"Hum. Mol. Genet."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"5199","DOI":"10.1073\/pnas.92.11.5199","article-title":"Hairpins are formed by the single DNA strands of the fragile X triplet repeats: Structure and biological implications","volume":"92","author":"Chen","year":"1995","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"53","DOI":"10.1007\/BF02703683","article-title":"Triplet repeat DNA structures and human genetic disease: Dynamic mutations from dynamic DNA","volume":"27","author":"Sinden","year":"2002","journal-title":"J. Biosci."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"1216","DOI":"10.1002\/humu.20600","article-title":"Closely linked cis-acting modifier of expansion of the CGG repeat in high risk FMR1 haplotypes","volume":"28","author":"Ennis","year":"2007","journal-title":"Hum. Mutat."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"599","DOI":"10.1083\/jcb.201404157","article-title":"Cis-acting DNA sequence at a replication origin promotes repeat expansion to a fragile X full mutation","volume":"206","author":"Gerhardt","year":"2014","journal-title":"J. Cell Biol."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"605","DOI":"10.1016\/S1525-1578(10)60594-6","article-title":"An enhanced polymerase chain reaction assay to detect pre- and full mutation alleles of the Fragile X Mental Retardation 1 gene","volume":"7","author":"Saluto","year":"2005","journal-title":"J. Mol. Diagn."},{"key":"ref_39","first-page":"1025","article-title":"Mental status of females with an FMR1 gene full mutation","volume":"58","author":"Wiegers","year":"1996","journal-title":"Am. J. Hum. Genet."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"431","DOI":"10.1586\/14737159.2015.1001749","article-title":"Single-tube methylation-specific duplex-PCR assay for rapid and accurate diagnosis of Fragile X Mental Retardation 1-related disorders","volume":"15","author":"Teo","year":"2015","journal-title":"Expert Rev. Mol. Diagn."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"121","DOI":"10.1101\/gr.141705.112","article-title":"Sequencing the unsequenceable: Expanded CGG-repeat alleles of the fragile X gene","volume":"23","author":"Loomis","year":"2013","journal-title":"Genome Res."},{"key":"ref_42","unstructured":"United Kingdom Genetic Testing Network (UKGTN) testing criteria for Fragile X Mental Retardation Syndrome. Available online: www.ukgtn.nhs.uk."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"322","DOI":"10.1002\/(SICI)1096-8628(19990402)83:4<322::AID-AJMG17>3.0.CO;2-B","article-title":"Fragile X premutation is a significant risk factor for premature ovarian failure: The International Collaborative POF in Fragile X Study\u2014preliminary data","volume":"83","author":"Chitayat","year":"1999","journal-title":"Am. J. Med. Genet."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"253","DOI":"10.1038\/sj.ejhg.5201510","article-title":"Nonlinear association between CGG repeat number and age of menopause in FMR1 premutation carriers","volume":"14","author":"Ennis","year":"2006","journal-title":"Eur. J. Hum. Genet."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"2396","DOI":"10.1093\/humrep\/dew204","article-title":"Length of FMR1 repeat alleles within the normal range does not substantially affect the risk of early menopause","volume":"31","author":"Ruth","year":"2016","journal-title":"Hum. Reprod."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"1335","DOI":"10.1093\/humrep\/deq058","article-title":"Intermediate sized CGG repeats are not a common cause of idiopathic premature ovarian failure","volume":"25","author":"Bennett","year":"2010","journal-title":"Hum. Reprod."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"19","DOI":"10.1038\/gim.2013.64","article-title":"Population-based estimates of the prevalence of FMR1 expansion mutations in women with early menopause and primary ovarian insufficiency","volume":"16","author":"Murray","year":"2014","journal-title":"Genet. Med."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"247","DOI":"10.1038\/sj.ejhg.5200451","article-title":"Reproductive and menstrual history of females with fragile X expansions","volume":"8","author":"Murray","year":"2000","journal-title":"Eur. J. Hum. Genet."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"460","DOI":"10.1001\/jama.291.4.460","article-title":"Penetrance of the Fragile X-associated Tremor\/Ataxia Syndrome in a premutation carrier population","volume":"291","author":"Jacquemont","year":"2004","journal-title":"JAMA"},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"963","DOI":"10.1373\/clinchem.2013.217331","article-title":"Early detection of Fragile X Syndrome: Applications of a novel approach for improved quantitative methylation analysis in venous blood and newborn blood spots","volume":"60","author":"Inaba","year":"2014","journal-title":"Clin. Chem."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"343","DOI":"10.1373\/clinchem.2015.244681","article-title":"Identification of males with cryptic Fragile X alleles by methylation-specific quantitative melt analysis","volume":"62","author":"Aliaga","year":"2016","journal-title":"Clin. Chem."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"339","DOI":"10.1089\/109065703322783725","article-title":"Incidence of Fragile X in 5,000 consecutive newborn males","volume":"7","author":"Badenas","year":"2003","journal-title":"Genetic Testing"},{"key":"ref_53","doi-asserted-by":"crossref","unstructured":"Tassone, F., Iong, K.P., Tong, T.-H., Lo, J., Gane, L.W., Berry-Kravis, E., Nguyen, D., Mu, L.Y., Laffin, J., and Bailey, D.B. (2012). FMR1 CGG allele size and prevalence ascertained through newborn screening in the United States. Genome Med.","DOI":"10.1186\/gm401"},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"351","DOI":"10.1086\/321974","article-title":"Fragile-X carrier screening and the prevalence of premutation and full-mutation carriers in Israel","volume":"69","author":"Magal","year":"2001","journal-title":"Am. J. Hum. Genet."},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"991","DOI":"10.1002\/pd.1815","article-title":"Preconceptual and prenatal screening for fragile X syndrome: Experience with 40 000 tests","volume":"27","author":"Berkenstadt","year":"2007","journal-title":"Prenat. Diagn."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"1147","DOI":"10.1016\/S0140-6736(95)90979-6","article-title":"Rapid antibody test for fragile X syndrome","volume":"345","author":"Willemsen","year":"1995","journal-title":"Lancet"},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"4972","DOI":"10.2174\/1381612821666150914121038","article-title":"Advances in the understanding of the gabaergic neurobiology of FMR1 expanded alleles leading to targeted treatments for Fragile X Spectrum disorder","volume":"21","author":"Lozano","year":"2015","journal-title":"Curr. Pharm. Des."},{"key":"ref_58","doi-asserted-by":"crossref","unstructured":"Kumari, D., and Usdin, K. (2016). Sustained expression of FMR1 mRNA from reactivated fragile X syndrome alleles after treatment with small molecules that prevent trimethylation of H3K27. Hum. Mol. Genet.","DOI":"10.1093\/hmg\/ddw215"}],"container-title":["Genes"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-4425\/7\/12\/110\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T19:27:43Z","timestamp":1760210863000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-4425\/7\/12\/110"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2016,11,30]]},"references-count":58,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2016,12]]}},"alternative-id":["genes7120110"],"URL":"https:\/\/doi.org\/10.3390\/genes7120110","relation":{},"ISSN":["2073-4425"],"issn-type":[{"value":"2073-4425","type":"electronic"}],"subject":[],"published":{"date-parts":[[2016,11,30]]}}}