title: Fragile X carrier screening and FMR1 allele distribution in the Japanese population.
abstract: Fragile X syndrome (FXS), which is the most common form of familial mental retardation, is caused by the expansion of the CGG repeat in the FMR1 gene on the X chromosome. Previous studies have suggested that as compared to other populations, Japanese have a lower prevalence of FXS. In addition, in the normal population, there are no carriers who have the premutation allele. We analyzed a total of 946 normal Japanese (576 males and 370 females) and attempted to estimate the frequency of the FMR1 allele. Within this population, we found that 1,155 alleles were in the normal range (less than 40 CGG repeats) and had a modal number of 27 repeats (35.75%). No carriers with premutations (55-200 CGG repeats) were observed in this normal population. We also identified six intermediate-sized alleles (40-54 CGG repeats), with a reported incidence of 1 in 103 males and 1 in 324 females. However, this allele frequency was different from that previously reported for the Japanese population. Since data from previous studies has suggested that FXS might possibly be associated with the genetic mechanism of autism, we also analyzed the length of the CGG repeats in 109 autistic patients. In all cases the CGG repeat numbers were within the normal range (16-36 repeats) and no individuals presented with expanded premutation or intermediate alleles. This finding indicates that the length of the CGG repeat within the FMR1 is unlikely to be responsible for autism in Japanese.
authors.affiliation: Research Center for Bioscience and Technology, Tottori University, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Otsuka
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Sakamoto
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Siomi
authors.forename: Mituo
authors.initials: M
authors.lastname: Itakura
authors.forename: Kenji
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Hideo
authors.initials: H
authors.lastname: Matumoto
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Sasaki
authors.forename: Nobumasa
authors.initials: N
authors.lastname: Kato
authors.forename: Eiji
authors.initials: E
authors.lastname: Nanba
mesh_terms: D044466:Asian People / Q000235:genetics*; D001321:Autistic Disorder / Q000235:genetics; D005260:Female; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics*; D005600:Fragile X Syndrome / Q000235:genetics*; D005787:Gene Frequency; D005820:Genetic Testing; D006579:Heterozygote; D006801:Humans; D008297:Male; D019680:Trinucleotide Repeat Expansion
chemical_list: D051860:Fragile X Messenger Ribonucleoprotein 1; C497683:FMR1 protein, human