Disease relevance of FRAXA

• Molecular diagnosis to exclude the fragile X (FRAXA) syndrome used the direct probe pfxa3, together with a control probe pS8 (DXS296), against PstI restriction digests of DNA [1].
• Deletions of the IDS gene can include a conserved locus that is tightly linked to FRAXA, suggesting that deletion of nearby genes may contribute to the variable clinical severity noted in Hunter syndrome [2].
• There is evidence that male subjects with a clinical picture of action tremor, Parkinsonism, and cerebellar ataxia may have Fragile X premutations (FRAXA) [3].
• Families with mentally retarded males found to be negative for FRAXA and FRAXE mutations are useful in understanding the genetic basis of X-linked mental retardation [4].
• We analyzed FRAXA and FRAXE triplet repeats in 203 male subjects with Parkinson's disease (PD) and 370 healthy controls [3].

Psychiatry related information on FRAXA

• Of the three X chromosome sites, FRAXA, FRAXE and FRAXF, the former two are associated with mental retardation in their expanded forms [5].
• We report the results of a five year survey of FRAXA and FRAXE mutations among boys aged 5 to 18 with special educational needs (SEN) related to learning disability [6].
• We examined comparably aged children and adolescents with FRAXA or autism to determine whether longitudinal changes in cognitive ability and adaptive behavior were similar in the two groups [7].
• Deletion of FMR1 in Purkinje cells enhances parallel fiber LTD, enlarges spines, and attenuates cerebellar eyelid conditioning in Fragile X syndrome [8].
• In addition, Fmr1 knockout animals exhibited increased locomotor activity, while no differences were found for aggression and anxiety [9].

High impact information on FRAXA

• Acetylated histones are associated with FMR1 in normal but not fragile X-syndrome cells [10].
• The most common FMR1 mutation is expansion of a CGG repeat tract at the 5' end of FMR1, which leads to cytosine methylation and transcriptional silencing [10].
• Our results represent the first description of loss of histone acetylation at a specific locus in human disease, and advance understanding of the mechanism of FMR1 transcriptional silencing [10].
• FRAXA expansion results in fragile X syndrome due to down regulation of expression of the FMR1 gene, which carries the hypermutable CGG repeat in the 5' untranslated portion of its first exon [5].
• A 5-kilobase EcoRI fragment derived from a cosmid coincident with the cytogenetic anomaly detects expanded, methylated and unstable sequences in five individuals who exhibit fragile sites in distal Xq; these individuals have normal repeat lengths at both FRAXA and FRAXE [11].

Chemical compound and disease context of FRAXA

• A further two families had consistent expression of a different folate sensitive fragile site, FRAXE, close to FRAXA but not associated with fragile X syndrome and not detectable with the pfxa3 probe [12].

Biological context of FRAXA

• This situation is similar to that seen at the FRAXA locus and is another example in which a trinucleotide repeat expansion is associated with a human genetic disorder [13].
• Three folate-sensitive fragile sites, termed FRAXA, FRAXE and FRAXF, have been identified on the distal end of chromosome Xq [11].
• Our results suggest that the threshold of repeat length for abnormal methylation and fragile-site expression may be smaller at FRAXE than at FRAXA [14].
• The locus DXS304 is closely linked to FRAXA, giving a peak lod score of 5.86 at a corresponding recombination fraction of .00 [15].
• To define more extensively this altered region of DNA replication, as well as to extend these studies to female cells containing premutant and mutant alleles, study of the replication timing properties of a >2-Mb zone in the FRAXA region (Xq27.3-q28) was undertaken by using a FISH technique [16].

Anatomical context of FRAXA

• The apparent enrichment for breakpoints lying within the Hprt-DXHX254E region is discussed in relation to both the nature of the embryonic stem cell fusions and the presence of the Fmr1 gene associated with FRAXA in man within this span [17].
• We have recently reported results of DNA replication analysis of three X-linked loci (FRAXA, F8C and XIST) on the X chromosomes in male and female fibroblasts using fluorescence in situ hybridization (FISH) (1) [18].
• Pathological studies from the brains of patients and from Fmr1 knockout mice show abnormal dendritic spines implicating FMRP in synapse formation and function [19].
• Physical mapping of new DNA probes near the fragile X mutation (FRAXA) by using a panel of cell lines [20].
• We report the validation and use of a cell hybrid panel which allowed us a rapid physical localization of new DNA probes in the vicinity of the fragile-X locus (FRAXA) [21].

Associations of FRAXA with chemical compounds

• We have developed an assay which allows simultaneous amplification of the triplet repeat sequences at the FRAXA and FRAXE loci by polymerase chain reaction, and detection of the products on non-denaturing gels stained with ethidium bromide [22].
• Treatment with acetyl-L-carnitine (ALC), a compound that reduces the in vitro expression of the FRAXA fragile site without affecting DNA methylation, caused an increase of H3 and H4 acetylation [23].
• By using the bisulfite protocol of the genomic sequencing method, we have determined the methylation patterns in this region on single chromosomes of healthy individuals and of selected premutation carriers and FRAXA patients [24].
• The overall evaluation of the in situ and genetic data reported suggest that the CDR locus 1) is located at the upper boundary of the FRAXA site; 2) is distal to DXS51 and proximal to DXS 389; and 3) segregates in a close linkage association with the loci DXS98 and DXS105 and, to a lesser extent, with the locus for MBS [25].
• Given this observation and knowing that the open reading frame of the mutated FMR1 gene is intact, we decided to investigate whether its activity could be restored in vitro by inducing DNA demethylation with 5-azadeoxycytidine (5-azadC) in fragile X patients' lymphoblastoid cells [26].

Regulatory relationships of FRAXA

• Therefore, it appears that FRAXD occurs very rarely in cultures treated to induce FRAXA since only one positive cell was observed in over 88,000 analyzed [27].

Other interactions of FRAXA

• It appears that very low frequencies of fra(X)(q27) can be accounted for only in part by the presence of the common fragile site since only one of 9 cases, each with one fra(X)(q27) positive cell, exhibited FRAXD and the others were FRAXA [27].
• In dealing with patients who are found to have fragile sites, other than FRAXA, FRAXE and possibly FRA11B, considerable reassurance can be given that they are not at increased risk of having children with congenital disease or developing disease themselves because of their fragile sites [28].
• In contrast to the rare fragile sites, including FRAXA, no repeat motifs, such as trinucleotide repeats, have been identified within FRA3B [29].
• Premutations of the fragile-X (FRAXA) gene were thought to have no clinical effects until recent reports of an increased incidence of premature ovarian failure in females and a late-onset neurological disorder in males [30].
• In this study of fragile X fra(X) syndrome families, the DXS105 locus was calculated to be proximal to FRAXA with a maximum lod score of 10.36 at theta = 0.08 [31].

Analytical, diagnostic and therapeutic context of FRAXA

• A simple multiplex FRAXA, FRAXE, and FRAXF PCR assay convenient for wide screening programs [32].
• FRAXA locus in fragile X diagnosis: family studies, prenatal diagnosis, and diagnosis of sporadic cases of mental retardation [33].
• METHODS: We screened by denaturing high-pressure liquid chromatography the entire coding region and flanking intronic sequences of the MECP2 gene in a cohort of 354 mentally retarded males found negative for an expansion across the FRAXA CGG repeat and in a family in which a boy and his sister were mentally retarded [34].
• The 25 FRAXA full mutations alleles detected were confirmed by Southern blot analysis [35].
• The diagnosis of fragile X A syndrome (FRAXA) during childhood depends largely on DNA-based diagnostic tests due to the lack of the specific clinical features [36].

References