Haplotype analysis at the FRAXA locus in Thai subjects.

Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand. lpornpro@yahoo.com

The prevalence of fragile X syndrome (FXS) is approximately 7% in Thai boys with developmental delay of unknown cause. To determine if FXS might have a specific haplotype association, we analyzed 125 unrelated control subjects and 25 unrelated FXS patients using 3 microsatellites, DXS548, FRAXAC1 and FRAXE, and two single nucleotide polymorphisms, ATL1 and IVS10. FRAXAC1 and DXS548 are located approximately 7 kb and approximately 150 kb proximal to the CGG-FMR1 whereas ATL1, IVS10 and FRAXE are located approximately 5.6 kb, approximately 24.5 kb and approximately 600 kb distal to the CGG-FMR1. We found 40 haplotypes in the control group and 14 haplotypes in the FXS group. Of 14 haplotypes in the FXS group, 6 haplotypes were not found in the control group suggesting possible new mutations or admixture of immigrant haplotypes. We observed that most diverse haplotypes came from different FRAXE alleles. For this reason, we analyzed haplotypes composed from the remaining markers alone (DXS548-FRAXAC1-ATL1-IVS10). We found 2 major haplotypes (20-18-G-T and 20-19-A-C) with no significant haplotype differences between the control group (67/125 of 20-18-G-T and 25/125 of 20-19-A-C) and FXS group (16/25 of 20-18-G-T and 6/25 of 20-19-A-C). The other haplotypes found were 33/125 in the control group and 3/25 in the FXS group. The two major haplotypes associated FXS in Thai subjects were the two most common haplotypes in the normal Thai subjects. We could not prove, therefore, that there were founder effects at the FRAXA locus in Thailand. We could not, however, exclude it completely. These findings apparently contrast with most other reports on FXS founder effects in various ethnic groups.

PMID: 11169559 [PubMed - indexed for MEDLINE]

Validity of analysis of FMRP expression in blood smears as a screening test for Fragile X Syndrome in the Indian population.

Genetic Research Centre, National Institute for Research in Reproductive Health, Parel Mumbai, Maharashtra, India.

Molecular diagnosis of Fragile X Syndrome (FXS) is carried out by PCR or Southern blot analysis on DNA isolated from leukocytes. These DNA analyses are time consuming and expensive, making it impractical for mass screening programs. We have recently standardized and tested the diagnostic potential of a rapid antibody test on blood smears, based on the presence of FMRP, the protein product of the FMR1 gene, in lymphocytes from normal individuals and the absence of FMRP in lymphocytes in patients with FXS. This test is essentially similar to the one developed at Erasmus University in the Netherlands, with suitable modifications. The diagnostic power of the antibody test is perfect for males, whereas the results are less specific for females. The cutoff value for affected male individuals, expressed as the percentage of FMRP-positive cells, was 20%. In normal individuals, the cutoff value was 85%. The results of the antibody test correlated well with that of Southern blots. Sensitivity of the test was 100% and specificity was 97.5%. This noninvasive test requires one or two drops of blood and is rapid, simple, and cheap, making it an ideal choice for large screening large groups of male mental retardates and neonates for FXS in developing countries such as India. Copyright 2005 Wiley-Liss, Inc.

PMID: 15900569 [PubMed - indexed for MEDLINE]

Is the 31 CAG repeat allele of the spinocerebellar ataxia 1 (SCA1) gene locus non-specifically associated with trinucleotide expansion diseases?

Faculty of Biology, University of Belgrade, Belgrade, Yugoslavia.

A number of human hereditary neuromuscular and neurodegenerative disorders are caused by the expansion of trinucleotide repeats within certain genes. The molecular mechanisms that underlie these expansions are not yet known. We have analyzed six trinucleotide repeat-containing loci [spinocerebellar ataxias (SCA1, SCA3, SCA8), dentatorubral-pallidoluysian atrophy (DRPLA), Huntington chorea (HD) and fragile X syndrome (FRAXA)] in myotonic dystrophy type 1 (DM1) patients (n = 52). As controls, we analyzed two groups of subjects: healthy control subjects (n =133), and a group of patients with non-triplet neuromuscular diseases (n = 68) caused by point mutations, deletions or duplications (spinal muscular atrophy, Charcot-Marie-Tooth disease, type 1A, hereditary neuropathy with liability to pressure palsies, and Duchenne and Becker muscular dystrophy). Allele frequency distributions for all tested loci were similar in these three groups with the exception of the SCA1 locus. In DM1 patients, the SCA1 allele with 31 CAG repeats account for 40.4% of all chromosomes tested, which is significantly higher than in two other groups (11.3% in healthy controls and 6.6% in the group of non-triplet diseased patients; P < 0.001, Fisher's exact test). This is consistent with our previous findings in HD patients. The absence of this association in non-triplet diseases as well as in healthy controls could indicate a possible role of this SCA1 allele with 31 repeats in triplet diseases. Here we discuss a possible role of the SCA1 region in pathological trinucleotide repeat expansions.

PMID: 11807410 [PubMed - indexed for MEDLINE]

Prevalence of the FMR1 mutation in Taiwan assessed by large-scale screening of newborn boys and analysis of DXS548-FRAXAC1 haplotype.

Department of Pathology, Chi Mei Medical Center, Tainan, Taiwan, Republic of China. tzeng-tainan@yahoo.com.tw

If carrier women could be identified in time and take appropriate measures, fragile X syndrome (FXS) can be prevented. Wide screening of women to be or in their early pregnancy was considered a good approach to identify carriers without misdetection. Nevertheless, we argued against the cost-effectiveness of implementing such a screening program in Taiwan, due to the lower carrier rate found in our pilot study. To reliably estimate the prevalence of mutant FMR1 gene in Taiwan, we anonymously screened 10,046 newborn boys using bloodspot polymerase chain reaction (PCR). Among them, the sample from one boy, who was most likely had FXS, failed repeatedly in PCR amplification. The estimated prevalence of premutation (55-200 CGG repeats) and intermediate alleles (45-54 CGG repeats) was 1:1,674 (n = 6) and 1:143 (n = 70), respectively. All these estimates were constantly lower than that reported in Caucasian populations, with variable statistic significance. Furthermore, when comparing analyses of the distribution of alleles at the two most often investigated microsatellite loci, DXS548 and FRAXAC1, between 100 control and 28 unrelated fragile X chromosomes, we found no apparent founder haplotype prevalent among the fragile X patients. Because a few founder haplotypes were reportedly prevalent in two thirds of fragile X alleles in Caucasians and in Chinese from Central China, we thus suggested that lack of founder fragile X chromosomes might result in a relatively low prevalence of mutant FMR1 gene in a population, as observed in Taiwan. (c) 2005 Wiley-Liss, Inc.

PMID: 15637705 [PubMed - indexed for MEDLINE]

Comment in:

Acta Paediatr Taiwan. 2004 Mar-Apr;45(2):67-8.

A step-wise diagnosis of fragile X syndrome in Taiwan.

Departments of Pediatrics, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan.

Fragile X syndrome (FXS), an X-linked dominant disorder, is one of the common forms of inherited mental retardation. This project aimed at identifying fragile X syndrome patients in schools by a two-step diagnosis with questionnaire and photography followed by molecular analysis. A total of 734 children with mental retardation were enrolled from kindergartens, primary schools, junior high schools, and schools for the mentally retarded. School teachers or nurses administered the questionnaires and took pictures of the faces and hands for of the patients. After viewing of the questionnaire and photos by a geneticist, 145 cases were selected for molecular study and 11 cases were identified as having full mutations in the FMRI gene. The detection rate was 1.5% (11 in 734) in all enrolled cases, and was 7.6% (11 in 145) in those who underwent molecular test. Those affected by FXS were more likely to have simian crease (p<0.001) and a head circumference larger than the 50th percentile (p=0.0295), and those who were not affected by FXS were lower in gestational age (p=0.0243). This screening method is useful for the detection of fragile X syndrome.

PMID: 15335113 [PubMed - indexed for MEDLINE]

[Polymorphism of trinucleotide repeats at loci FRAXA and FRAXE in the population of Tomsk]

Institute of Medical Genetics, Tomsk Research Center, Russian Academy of Medical Sciences, Tomsk, 634050 Russia.

Polymorphism of CGG and GCC trinucleotide repeats, whose expansions at the FRAXA and FRAXE loci have been identified as causative mutations in two forms of mental retardation, was studied in Slavic population of Tomsk. At the FRAXA locus a total of 31 allelic variants ranging from 8 to 56 copies of CGG repeat with two modal classes of 28-29 and 18-20 repeat units (with the frequencies of 24.6 and 11.5% respectively) were revealed. Compared to other populations, this locus was characterized by unusually high frequency of intermediate alleles with the sizes of more than 40 CGG repeat units (12.4%). Since intermediate repeats of the FRAXA locus were more prone to instability than normal alleles, it was suggested that Slavic population of Siberia had higher risk of the development of FMR1 dynamic mutations, giving rise to the Martin-Bell syndrome. The FRAXE allele frequency distribution was demonstrated to be normal with 18 allelic variants ranging from 9 to 27 GCC repeat units. In the population of Tomsk this locus had higher than in other populations frequency (26.7%) of short (less than 15 repeat units in size) alleles. In addition, in the Tomsk population both loci were characterized by high level of heterozygosity and low frequencies of modal allele classes. These results can be explained by the high level of outbreeding typical of the population of Siberia.

PMID: 11898618 [PubMed - indexed for MEDLINE]

Fragile X syndrome: a clinico-genetic study of mentally retarded patients in Kuwait.

Kuwait Medical Genetics Centre, Kuwait.

In a prospective study in Kuwait, 182 mentally retarded male patients who fulfilled 5 or more clinical criteria of fragile X syndrome were screened using polymerase chain reaction (PCR) testing. Twenty patients (11%) were highly suspected of having fragile X syndrome due to mutation at the FRAXA locus; none had mutation at the FRAXE locus. Of these, 11 (55%) were confirmed fragile-X-positive by both cytogenetic and PCR techniques. The most frequent clinical features were: prominent forehead, high arched palate, hyperextensible joints, long ears, prominent jaw, height > 10th centile and attention-deficit hyperactivity. Less common were avoidance of eye contact (45%), autism (45%) and seizures (30%). Large testes were found in 55% of cases. Pre-pubertal and post-pubertal clinical criteria were different.

PMID: 16201716 [PubMed - indexed for MEDLINE]

Fragile X syndrome carrier screening in the prenatal genetic counseling setting.

Genetic Services and Molecular Diagnostic Laboratory, Genzyme Genetics, Westborough, Massachusetts, USA.

PURPOSE: To document our experience with fragile X carrier screening. METHODS: In this study, 29,103 women with no known or suspected family history of fragile X syndrome were offered fragile X carrier screening during their prenatal genetic counseling visit. Screening acceptance was analyzed by referral indication, carrier frequencies documented, and prenatal outcome data presented. RESULTS: Overall, 7.9% accepted carrier screening. The premutation frequency was 1 in 382, and the intermediate allele frequency was 1 in 143. CONCLUSIONS: Fragile X screening is a desirable option for some women seeking prenatal genetic counseling and should be made available to this population.

PMID: 15834242 [PubMed - indexed for MEDLINE]

Prevalence of the fragile X syndrome in Yugoslav patients with non-specific mental retardation.

Faculty of Biology, School of Medicine, University Belgrade,11000, Yugoslavia.

Mutations at two fragile sites, FRAXA and FRAXE, loci are caused by an expansion of a CGG/GCC trinucleotide repeat and are characterized by mental retardation. Here we report molecular screening survey of 97 unrelated individuals diagnosed with non-specific mental retardation (MR), which produced positive test for FRAXA in two boys and none positive for the FRAXE mutation. In addition, we studied allelic frequency distribution for the FRAXA locus in this group of mentally retarded patients, as well as in the 99 healthy subjects of Yugoslav population. The distribution of FMR1 CGG repeat size in both groups was similar: the most common allele contained 29 repeats (32.86% in the healthy population and 54.54% in MR population), followed by the allele with 28 CGG repeats (21.43% in the healthy and 12.2% in MR population). Premutation alleles with more than 45 repeats were not found in control nor in the MR group.

PMID: 14668200 [PubMed - indexed for MEDLINE]

Fragile X premutation alleles in SCA, ET, and parkinsonism in an Asian cohort.

Department of Neurology, Singapore General Hospital, Outram Road, Singapore 169608. gnrtek@sgh.com.sg

Among 367 subjects, the authors analyzed 167 patients with essential tremor, sporadic progressive cerebellar ataxia, multiple-system atrophy, and atypical parkinsonism and 200 healthy control subjects for FMR1 premutation alleles. None of the subjects carried alleles within the premutation range. These findings suggest that in the absence of other supportive clinical or imaging features, the cost-effectiveness of routine fragile X tremor/ataxia syndrome screening in this Asian cohort with movement disorders was low.

PMID: 15277639 [PubMed - indexed for MEDLINE]

Fragile X gene premutation in multiple system atrophy.

Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232-2195, USA.

Previous reports have suggested that expansion of the CGG repeat located in the fragile X mental retardation 1 (FMR1) gene might be responsible for a significant number of patients with the multiple system atrophy (MSA) phenotype. Analysis of 65 MSA patients found only 4.6% displayed CGG expansions in the suspected range. This is similar to the frequency reported in the normal population, suggesting that this expansion does not play a major role in the MSA phenotype.

PMID: 15546601 [PubMed - indexed for MEDLINE]