title: EMQN best practice guidelines for the molecular genetic testing and reporting of fragile X syndrome and other fragile X-associated disorders.
abstract: Different mutations occurring in the unstable CGG repeat in 5' untranslated region of FMR1 gene are responsible for three fragile X-associated disorders. An expansion of over ∼200 CGG repeats when associated with abnormal methylation and inactivation of the promoter is the mutation termed 'full mutation' and is responsible for fragile X syndrome (FXS), a neurodevelopmental disorder described as the most common cause of inherited intellectual impairment. The term 'abnormal methylation' is used here to distinguish the DNA methylation induced by the expanded repeat from the 'normal methylation' occurring on the inactive X chromosomes in females with normal, premutation, and full mutation alleles. All male and roughly half of the female full mutation carriers have FXS. Another anomaly termed 'premutation' is characterized by the presence of 55 to ∼200 CGGs without abnormal methylation, and is the cause of two other diseases with incomplete penetrance. One is fragile X-associated primary ovarian insufficiency (FXPOI), which is characterized by a large spectrum of ovarian dysfunction phenotypes and possible early menopause as the end stage. The other is fragile X-associated tremor/ataxia syndrome (FXTAS), which is a late onset neurodegenerative disorder affecting males and females. Because of the particular pattern and transmission of the CGG repeat, appropriate molecular testing and reporting is very important for the optimal genetic counselling in the three fragile X-associated disorders. Here, we describe best practice guidelines for genetic analysis and reporting in FXS, FXPOI, and FXTAS, including carrier and prenatal testing.
authors.affiliation: Laboratoire Diagnostic Génétique, Faculté de Médecine-CHRU, Strasbourg, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Biancalana
authors.affiliation: Genetikum, Center for Human Genetics, Neu-Ulm, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Glaeser
authors.affiliation: National Centre for Medical Genetics, Our Lady's Children's Hospital, Crumlin, Dublin, Ireland.
authors.forename: Shirley
authors.initials: S
authors.lastname: McQuaid
authors.affiliation: Institute of Human Genetics, University Hospital of Ulm, Ulm, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Steinbach
mesh_terms: D020121:5' Untranslated Regions; D000483:Alleles; D001259:Ataxia / Q000175:diagnosis* / Q000235:genetics; D019175:DNA Methylation; D005260:Female; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics*; D005600:Fragile X Syndrome / Q000175:diagnosis* / Q000235:genetics; D005820:Genetic Testing / Q000592:standards*; D006801:Humans; D008297:Male; D009154:Mutation; D010641:Phenotype; D017410:Practice Guidelines as Topic; D016649:Primary Ovarian Insufficiency / Q000175:diagnosis* / Q000235:genetics; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D014202:Tremor / Q000175:diagnosis* / Q000235:genetics
chemical_list: D020121:5' Untranslated Regions; D051860:Fragile X Messenger Ribonucleoprotein 1; D012333:RNA, Messenger; C497683:FMR1 protein, human