title: Identification of fragile X pre-mutation carriers in the Chinese obstetric population using a robust FMR1 polymerase chain reaction assay: implications for screening and prenatal diagnosis.
abstract: BACKGROUND
  There is significant morbidity associated with fragile X syndrome. Unfortunately, most maternal carriers are clinically silent during their reproductive years. Because of this, many experts have put forward the notion of preconception or prenatal fragile X carrier screening for females. This study aimed to determine the prevalence of fragile X syndrome pre-mutation and asymptomatic full-mutation carriers in a Chinese pregnant population, and the distribution of cytosine-guanine-guanine (CGG) repeat numbers using a robust fragile X mental retardation 1 (FMR1) polymerase chain reaction assay.
  
  
  METHODS
  This was a cross-sectional survey in prospectively recruited pregnant women from a university hospital in Hong Kong. Chinese pregnant women without a family history of fragile X syndrome were recruited between April 2013 and May 2015. A specific FMR1 polymerase chain reaction assay was performed on peripheral blood to determine the CGG repeat number of the FMR1 gene. Prenatal counselling was offered to full-mutation and pre-mutation carriers.
  
  
  RESULTS
  In 2650 Chinese pregnant women, two individuals with pre-mutation alleles (0.08%, one in 1325) and one asymptomatic woman with full-mutation (0.04%, one in 2650) alleles were identified. The overall prevalence of pre-mutation and full-mutation alleles was 0.11% (1 in 883). Furthermore, 30 (1.1%) individuals with intermediate alleles were detected. In the 2617 women with normal CGG repeats, the most common CGG repeat allele was 30.
  
  
  CONCLUSIONS
  The overall prevalence of pre-mutation and asymptomatic full-mutation carriers in the Chinese pregnant population was one in 883, detected by a new FMR1 polymerase chain reaction assay.
authors.affiliation: Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong, Shatin, Hong Kong.
authors.forename: Y Ky
authors.initials: YK
authors.lastname: Cheng
authors.affiliation: Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong, Shatin, Hong Kong.
authors.forename: C Sw
authors.initials: CS
authors.lastname: Lin
authors.affiliation: Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong, Shatin, Hong Kong.
authors.forename: Y Ky
authors.initials: YK
authors.lastname: Kwok
authors.affiliation: Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong, Shatin, Hong Kong.
authors.forename: Y M
authors.initials: YM
authors.lastname: Chan
authors.affiliation: Fetal Medicine Centre, Paramount Medical Centre, Hong Kong.
authors.forename: T K
authors.initials: TK
authors.lastname: Lau
authors.affiliation: Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong, Shatin, Hong Kong.
authors.forename: T Y
authors.initials: TY
authors.lastname: Leung
authors.affiliation: Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong, Shatin, Hong Kong.
authors.forename: K W
authors.initials: KW
authors.lastname: Choy
mesh_terms: D000328:Adult; D000483:Alleles; D003430:Cross-Sectional Studies; D005260:Female; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics*; D005600:Fragile X Syndrome / Q000453:epidemiology* / Q000235:genetics*; D006580:Genetic Carrier Screening / Q000379:methods*; D005820:Genetic Testing; D006579:Heterozygote; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D009154:Mutation; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D011446:Prospective Studies
chemical_list: D051860:Fragile X Messenger Ribonucleoprotein 1; C497683:FMR1 protein, human
keywords: Fragile X syndrome; Mutation; Prenatal diagnosis