Flora Tassone

Fragile X premutation tremor/ataxia syndrome: molecular, clinical, and neuroimaging correlates.

We present a series of 26 patients, all >50 years of age, who are carriers of the fragile X premutation and are affected by a multisystem, progressive neurological disorder. The two main clinical features of this new syndrome are cerebellar ataxia and/or intention tremor, which were chosen as clinical inclusion criteria for this series. Other documented symptoms were short-term memory loss, executive function deficits, cognitive decline, parkinsonism, peripheral neuropathy, lower limb proximal muscle weakness, and autonomic dysfunction. Symmetrical regions of increased T2 signal intensity in the middle cerebellar peduncles and adjacent cerebellar white matter are thought to be highly sensitive for this neurologic condition, and their presence is the radiological inclusion criterion for this series. Molecular findings include elevated mRNA and low-normal or mildly decreased levels of fragile X mental retardation 1 protein. The clinical presentation of these patients, coupled with a specific lesion visible on magnetic resonance imaging and with neuropathological findings, affords a more complete delineation of this fragile X premutation-associated tremor/ataxia syndrome and distinguishes it from other movement disorders.

Fragile-X–Associated Tremor/Ataxia Syndrome (FXTAS) in Females with the FMR1 Premutation

We describe five female carriers of the FMR1 premutation who presented with symptoms of tremor and ataxia and who received a diagnosis of definite or probable fragile-X-associated tremor/ataxia syndrome (FXTAS). Unlike their male counterparts with FXTAS, none of the women had dementia. Females had not been reported in previous studies of FXTAS, suggesting that they may be relatively protected from this disorder. Brain tissue was available from one of the five subjects, a women who died at age 85 years; microscopic examination revealed intranuclear neuronal and astrocytic inclusions, in accord with the findings previously reported in males with FXTAS. The work-up of families with the FMR1 mutation should include questions regarding neurological symptoms in both older male and female carriers, with the expectation that females may also manifest the symptoms of FXTAS, although more subtly and less often than their male counterparts.

Autism Profiles of Males With Fragile X Syndrome.

Autism, which is common in individuals with fragile X syndrome, is often difficult to diagnose. We compared the diagnostic classifications of two measures for autism diagnosis, the ADOS and the ADI-R, in addition to the DSM-IV-TR in 63 males with this syndrome. Overall, 30% of the subjects met criteria for autistic disorder and 30% met criteria for PDD-NOS. The classifications on the ADOS and DSM-IV-TR were most similar, whereas the ADI-R classified subjects as autistic much more frequently. We further investigated the relationship of both FMRP and FMRI mRNA to symptoms of autism in this cohort and found no significant relationship between the measures of autism and molecular features, including FMRP, FMRI mRNA, and CGG repeat number.

A Rapid Polymerase Chain Reaction-Based Screening Method for Identification of All Expanded Alleles of the Fragile X (FMR1) Gene in Newborn and High-Risk Populations

Fragile X syndrome, the most common inherited cause of intellectual impairment and the most common single gene associated with autism, generally occurs for fragile X mental retardation 1 (FMR1) alleles that exceed 200 CGG repeats (full-mutation range). Currently, there are no unbiased estimates of the number of full-mutation FMR1 alleles in the general population; a major obstacle is the lack of an effective screening tool for expanded FMR1 alleles in large populations. We have developed a rapid polymerase chain reaction (PCR)-based screening tool for expanded FMR1 alleles. The method utilizes a chimeric PCR primer that targets randomly within the expanded CGG region, such that the presence of a broad distribution of PCR products represents a positive result for an expanded allele. The method is applicable for screening both males and females and for allele sizes throughout the premutation (55 to 200 CGG repeats) and full-mutation ranges. Furthermore, the method is capable of rapid detection of expanded alleles using as little as 1% of the DNA from a single dried blood spot. The methodology presented in this work is suitable for screening large populations of newborn or those at high risk (eg, autism, premature ovarian failure, ataxia, dementia) for expanded FMR1 alleles. The test described herein costs less than

Mitochondrial dysfunction in autism.

5 per sample for materials; with suitable scale-up and automation, the cost should approach

Fragile X-associated tremor/ataxia syndrome: clinical features, genetics, and testing guidelines.

1 per sample.

Expanded clinical phenotype of women with the FMR1 premutation

CONTEXT Impaired mitochondrial function may influence processes highly dependent on energy, such as neurodevelopment, and contribute to autism. No studies have evaluated mitochondrial dysfunction and mitochondrial DNA (mtDNA) abnormalities in a well-defined population of children with autism. OBJECTIVE To evaluate mitochondrial defects in children with autism. DESIGN, SETTING, AND PATIENTS Observational study using data collected from patients aged 2 to 5 years who were a subset of children participating in the Childhood Autism Risk From Genes and Environment study in California, which is a population-based, case-control investigation with confirmed autism cases and age-matched, genetically unrelated, typically developing controls, that was launched in 2003 and is still ongoing. Mitochondrial dysfunction and mtDNA abnormalities were evaluated in lymphocytes from 10 children with autism and 10 controls. MAIN OUTCOME MEASURES Oxidative phosphorylation capacity, mtDNA copy number and deletions, mitochondrial rate of hydrogen peroxide production, and plasma lactate and pyruvate. RESULTS The reduced nicotinamide adenine dinucleotide (NADH) oxidase activity (normalized to citrate synthase activity) in lymphocytic mitochondria from children with autism was significantly lower compared with controls (mean, 4.4 [95% confidence interval {CI}, 2.8-6.0] vs 12 [95% CI, 8-16], respectively; P = .001). The majority of children with autism (6 of 10) had complex I activity below control range values. Higher plasma pyruvate levels were found in children with autism compared with controls (0.23 mM [95% CI, 0.15-0.31 mM] vs 0.08 mM [95% CI, 0.04-0.12 mM], respectively; P = .02). Eight of 10 cases had higher pyruvate levels but only 2 cases had higher lactate levels compared with controls. These results were consistent with the lower pyruvate dehydrogenase activity observed in children with autism compared with controls (1.0 [95% CI, 0.6-1.4] nmol × [min × mg protein](-1) vs 2.3 [95% CI, 1.7-2.9] nmol × [min × mg protein](-1), respectively; P = .01). Children with autism had higher mitochondrial rates of hydrogen peroxide production compared with controls (0.34 [95% CI, 0.26-0.42] nmol × [min × mg of protein](-1) vs 0.16 [95% CI, 0.12-0.20] nmol × [min × mg protein](-1) by complex III; P = .02). Mitochondrial DNA overreplication was found in 5 cases (mean ratio of mtDNA to nuclear DNA: 239 [95% CI, 217-239] vs 179 [95% CI, 165-193] in controls; P = 10(-4)). Deletions at the segment of cytochrome b were observed in 2 cases (ratio of cytochrome b to ND1: 0.80 [95% CI, 0.68-0.92] vs 0.99 [95% CI, 0.93-1.05] for controls; P = .01). CONCLUSION In this exploratory study, children with autism were more likely to have mitochondrial dysfunction, mtDNA overreplication, and mtDNA deletions than typically developing children.

Sam68 sequestration and partial loss of function are associated with splicing alterations in FXTAS patients

Fragile X‐associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder with core features of action tremor and cerebellar gait ataxia. Frequent associated findings include parkinsonism, executive function deficits and dementia, neuropathy, and dysautonomia. Magnetic Resonance Imaging studies in FXTAS demonstrate increased T2 signal intensity in the middle cerebellar peduncles (MCP sign) in the majority of patients. Similar signal alterations are seen in deep and subependymal cerebral white matter, as is general cortical and subcortical atrophy. The major neuropathological feature of FXTAS is the presence of intranuclear, neuronal, and astrocytic, inclusions in broad distribution throughout the brain and brainstem. FXTAS is caused by moderate expansions (55–200 repeats; premutation range) of a CGG trinucleotide in the fragile X mental retardation 1 (FMR1) gene, the same gene which causes fragile X syndrome when in the full mutation range (200 or greater CGG repeats). The pathogenic mechanism is related to overexpression and toxicity of the FMR1 mRNA per se. Although only recently discovered, and hence currently under‐diagnosed, FXTAS is likely to be one of the most common single‐gene disorders leading to neurodegeneration in males. In this report, we review information available on the clinical, radiological, and pathological features, and prevalence and management of FXTAS. We also provide guidelines for the practitioner to assist with identifying appropriate patients for DNA testing for FXTAS, as well as recommendations for genetic counseling once a diagnosis of FXTAS is made.

Abnormal elevation of FMR1 mRNA is associated with psychological symptoms in individuals with the fragile X premutation

Fragile X‐associated tremor/ataxia syndrome (FXTAS) is generally considered to be uncommon in older female carriers of premutation alleles (55–200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene; however, neither prevalence, nor the nature of the clinical phenotype, has been well characterized in female carriers. In this study, we evaluated 146 female carriers (mean, 42.3 years; range, 20–75 years) with and without core features of FXTAS (tremor; gait ataxia), and 69 age‐matched controls (mean, 45.8 years; range, 21–78 years). Compared with controls, carriers with definite or probable FXTAS had greater medical co‐morbidity, with increased prevalence of thyroid disease (P = 0.0096), hypertension (P = 0.0020), seizures (P = 0.0077), peripheral neuropathy (P = 0.0040), and fibromyalgia (P = 0.0097), in addition to the typical symptoms of FXTAS–tremor (P < 0.0001) and ataxia (P < 0.0001). The non‐FXTAS premutation group had more complaints of chronic muscle pain (P = 0.0097), persistent paraesthesias in extremities (P < 0.0001), and history of tremor (P < 0.0123) than controls. The spectrum of clinical involvement in female carriers with FXTAS is quite broad, encompassing a number of medical co‐morbidities as well as the core movement disorder. The remarkable degree of thyroid dysfunction (17% in the non‐FXTAS group and 50% in the FXTAS group) warrants consideration of thyroid function studies in all female premutation carriers, particularly those with core features of FXTAS.

Maternal periconceptional folic acid intake and risk of autism spectrum disorders and developmental delay in the CHARGE (CHildhood Autism Risks from Genetics and Environment) case-control study

Fragile X‐associated Tremor/Ataxia Syndrome (FXTAS) is a neurodegenerative disorder caused by expansion of 55–200 CGG repeats in the 5′‐UTR of the FMR1 gene. FXTAS is characterized by action tremor, gait ataxia and impaired executive cognitive functioning. It has been proposed that FXTAS is caused by titration of RNA‐binding proteins by the expanded CGG repeats. Sam68 is an RNA‐binding protein involved in alternative splicing regulation and its ablation in mouse leads to motor coordination defects. Here, we report that mRNAs containing expanded CGG repeats form large and dynamic intranuclear RNA aggregates that recruit several RNA‐binding proteins sequentially, first Sam68, then hnRNP‐G and MBNL1. Importantly, Sam68 is sequestered by expanded CGG repeats and thereby loses its splicing‐regulatory function. Consequently, Sam68‐responsive splicing is altered in FXTAS patients. Finally, we found that regulation of Sam68 tyrosine phosphorylation modulates its localization within CGG aggregates and that tautomycin prevents both Sam68 and CGG RNA aggregate formation. Overall, these data support an RNA gain‐of‐function mechanism for FXTAS neuropathology, and suggest possible target routes for treatment options.