title: Molecular testing for Fragile X Syndrome: lessons learned from 119,232 tests performed in a clinical laboratory.
abstract: OBJECTIVE
  To examine the data from over 119,000 Fragile X Syndrome tests and 307 prenatal tests to detect unsuspected findings and obtain clinical data when indicated to optimize genetic counseling.
  
  
  METHODS
  A proprietary database containing 119,232 consecutive postnatal and 307 prenatal FXS tests performed between November 2, 1992 and June 1, 2006 was queried.
  
  
  RESULTS
  The distribution of normal FMR1 alleles was a bimodal distribution with a major peak at 30 repeats and a minor peak at 21 repeats. Of 59,707 tests performed for males, 1.4% had a fully expanded and methylated FMR1 allele. Of 59,525 tests performed for females, 0.61% had an affected FMR1 allele, and 1.7% had a premutation FMR1 allele for a total carrier frequency of 1.3%. When fetuses inherited an expanded maternal allele, the risk of expansion to a full affected allele was 0%, 5%, 30% and 100% for allele sizes of <50, 50-75, 76-100 and >100 repeats, respectively.
  
  
  CONCLUSIONS
  These figures can be used for genetic counseling of patients presenting for carrier detection and prenatal diagnosis for Fragile X Syndrome.
authors.affiliation: Nichols Institute, Quest Diagnostics, 33608 Ortega Highway, San Juan Capistrano, California 92690, USA. charles.m.strom@questdiagnostics.com
authors.forename: Charles M
authors.initials: CM
authors.lastname: Strom
authors.forename: Beryl
authors.initials: B
authors.lastname: Crossley
authors.forename: Joy B
authors.initials: JB
authors.lastname: Redman
authors.forename: Arlene
authors.initials: A
authors.lastname: Buller
authors.forename: Franklin
authors.initials: F
authors.lastname: Quan
authors.forename: Mei
authors.initials: M
authors.lastname: Peng
authors.forename: Matthew
authors.initials: M
authors.lastname: McGinnis
authors.forename: Raymond G
authors.initials: RG
authors.lastname: Fenwick
authors.forename: Weimin
authors.initials: W
authors.lastname: Sun
mesh_terms: D000328:Adult; D002648:Child; D005260:Female; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics*; D005600:Fragile X Syndrome / Q000175:diagnosis* / Q000453:epidemiology / Q000235:genetics; D005787:Gene Frequency; D005817:Genetic Counseling; D005820:Genetic Testing; D006579:Heterozygote; D006801:Humans; D007753:Laboratories; D008297:Male; D011296:Prenatal Diagnosis; D019680:Trinucleotide Repeat Expansion
chemical_list: D051860:Fragile X Messenger Ribonucleoprotein 1; C497683:FMR1 protein, human