Trinucleotide CGG repeat in theFMR1 gene in Chinese mentally retarded patients

Abstract

The fragile X syndrome of mental retardation is related to the number of trinucleotide CGG repeats at the 5'-untranslated region of the FMR1 gene located on the X-chromosome. We have studied X-chromosomes from 649 unaffected Chinese subjects and 324 patients with mild mental retardation. All study subjects were unrelated. The CGG repeat number was analysed by electrophoresis of a polymerase chain reaction followed by gel transfer and hybridisation with a 32P-labeled (CCG)5 probe. The DNA samples having detectable CGG expansion were further analysed by Southern blot analysis with probe StB12.3 after restriction digestion by EcoR I and Eag I. For the unaffected Chinese subjects, a different distribution pattern of CGG allele size from Caucasians was observed. It was a bimodal pattern and the CGG repeat number ranged from 19 to 54. The most common CGG repeat allele was 29 compared with 30 in Caucasians. The second mode appeared at 36 repeats. There was mild statistical difference in the repeat patterns between the mentally retarded patients and unaffected subjects, although the essential features were similar. Among the mentally retarded patients, one male had an unmethylated full mutation and one female had a full mutation. The fragile X prevalence was 0.6%, which is lower than two previous studies in Chinese mentally retarded patients utilising cytogenetic analysis. Our results indicate that a large-scale screening program would be worthwhile to determine the prevalence of the fragile X syndrome in the Chinese population.

Fragile X syndrome screening in Chinese children with unknown intellectual developmental disorder

“…The FXS yield from the patients in this study is also different from that reported in previous Chinese IDD/MR populations [ 18 , 19 ]. Zhong et al performed multi-institutional screening of 1127 adult/child individuals with mild-moderate IDD, and found that 2.8 % of the Chinese IDD patients carry a full mutation.…”

“…The prevalence of FXS in a Chinese IDD population has been previously reported [ 18 , 19 ] However, the rate of FXS in IDD children seeking diagnosis/treatment in mainland China is unknown. The availability of such information is expected to help enhance awareness among neurologists in suspicious populations and improve options for intervention and treatment.…”

Distribution of CGG repeats and FRAXAC1/DXS548 alleles in South American populations

“…In quilombos, the absence of the peak around 19 or 20 copies might explain somewhat the lower expected heterozygosity of CGG repeats in African Brazilians, when compared to those of São Paulo (Table III). In Japanese [Arinami et al, 1993], Chinese [Pang et al, 1999], and other Asians [Eichler et al, 1995; Chen et al, 1997], this peak does not occur either. Our results corroborate that the high frequency of 19 or 20 copies is a European peculiarity.…”

“…One could speculate that this allele increased its frequency in Western Europe, probably much later than the early dispersals from ancestral populations coming from Africa. In Asians, a second peak around 36 or 37 copies seems to be characteristic [Arinami et al, 1993; Eichler et al, 1995; Chen et al, 1997; Pang et al, 1999]. The higher frequency of 20‐copy alleles among Europeans and 36‐copy alleles among Asians seem to be a signature of founder effects in groups that gave rise to the present Asian and Western European populations.…”

Fragile X Syndrome: Prevalence, Treatment, and Prevention in China

“…Only 0.6% of 324 patients met the FXS diagnostic criteria. According to this result, the prevalence of FXS among Chinese individuals with ID is lower than in Western countries (12). Tzeng et al (13) evaluated the mutant rate of the FMR1 gene among 10,046 neonatal boys in Taiwan.…”