title: CGG allele size somatic mosaicism and methylation in FMR1 premutation alleles.
abstract: BACKGROUND
  Greater than 200 CGG repeats in the 5'UTR of the FMR1 gene lead to epigenetic silencing and lack of the FMR1 protein, causing fragile X Syndrome. Individual carriers of a premutation (PM) allele with 55-200 CGG repeats are typically unmethylated and can present with clinical features defined as FMR1-associated conditions.
  
  
  METHODS
  Blood samples from 17 male PM carriers were assessed clinically and molecularly by Southern blot, western blot, PCR and QRT-PCR. Blood and brain tissue from an additional 18 PM males were also similarly examined. Continuous outcomes were modelled using linear regression and binary outcomes were modelled using logistic regression.
  
  
  RESULTS
  Methylated alleles were detected in different fractions of blood cells in all PM cases (n=17). CGG repeat numbers correlated with percent of methylation and mRNA levels and, especially in the upper PM range, with greater number of clinical involvements. Inter-tissue/intra-tissue somatic instability and differences in percent methylation were observed between blood and fibroblasts (n=4) and also observed between blood and different brain regions in three of the 18 PM cases examined. CGG repeat lengths in lymphocytes remained unchanged over a period of time ranging from 2 to 6 years, three cases for whom multiple samples were available.
  
  
  CONCLUSIONS
  In addition to CGG size instability, individuals with a PM expanded allele can exhibit methylation and display more clinical features likely due to RNA toxicity and/or FMR1 silencing. The observed association between CGG repeat length and percent of methylation with the severity of the clinical phenotypes underscores the potential value of methylation in affected PM to further understand penetrance, inform diagnosis and expand treatment options.
authors.affiliation: Department of Biochemistry and Molecular Medicine, University of California Davis, School of Medicine, Sacramento, California, USA.
authors.forename: Dalyir I
authors.initials: DI
authors.lastname: Pretto
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Mendoza-Morales
authors.forename: Joyce
authors.initials: J
authors.lastname: Lo
authors.forename: Ru
authors.initials: R
authors.lastname: Cao
authors.forename: Andrew
authors.initials: A
authors.lastname: Hadd
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Latham
authors.forename: Blythe
authors.initials: B
authors.lastname: Durbin-Johnson
authors.forename: Randi
authors.initials: R
authors.lastname: Hagerman
authors.forename: Flora
authors.initials: F
authors.lastname: Tassone
mesh_terms: D000293:Adolescent; D000368:Aged; D000483:Alleles; D002648:Child; D002675:Child, Preschool; D019175:DNA Methylation; D005347:Fibroblasts; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics* / Q000378:metabolism; D005600:Fragile X Syndrome / Q000209:etiology / Q000235:genetics; D006579:Heterozygote; D006801:Humans; D008297:Male; D009030:Mosaicism; D009154:Mutation; D019680:Trinucleotide Repeat Expansion; D055815:Young Adult
chemical_list: D051860:Fragile X Messenger Ribonucleoprotein 1; C497683:FMR1 protein, human
keywords: Diagnosis; Genetics; Movement disorders (other than Parkinsons)