Biomedical subjects

Flora Tassone

Publications and source records attributed to Flora Tassone.

32 records · Page 2Linked to original sources

PubMed2004

The effect of pre-mutation of X chromosome CGG trinucleotide repeats on brain anatomy.

Expanded trinucleotide repeats are associated with several neuropsychiatric disorders, including fragile X syndrome (FraX) which is the most common inherited form of mental retardation. It is currently thought that FraX results from having >200 CGG trinucleotide repeats, with consequent methylation of the fragile X mental retardation gene (FMR1) and loss of FMR1 protein (FMRP). Pre-mutation carriers of FraX (with 55-200 CGG trinucleotide repeats) were originally considered unaffected, although recent studies challenge this view. However, there are few studies on the effect of pre-mutation trinucleotide repeat expansion on the male human brain using quantitative MRI. Also the results of prior investigations may be confounded because people were selected on the basis of clinical and neurological features, and not genetic phenotype. We compared the brain anatomy of 20 adult male pre-mutation members of known FraX families with 20 healthy male controls. The two groups did not differ significantly in age, intelligence quotient (IQ) or handedness. We also investigated whether any observed effects were associated with: (i) ageing; (ii) expansion of pre-mutation CGG trinucleotide repeats; (iii) reduction in the percentage of lymphocytes staining with anti-FMRP antibodies [%FMRP(+) lymphocytes]; and (iv) elevation of FMR1 mRNA levels. Male pre-mutation carriers of FraX, compared with matched controls, had significantly less voxel density in several brain regions, including the cerebellum, amygdalo-hippocampal complex and thalamus. Within pre-mutation carriers of FraX, ageing, increases in the number of CGG trinucleotide repeats and decreases in %FMRP(+) lymphocytes were associated with decreasing voxel density of regions previously identified as decreased relative to controls. Regional grey and white matter density is significantly affected in male pre-mutation carriers of FraX recruited on the basis of genetic, not clinical, phenotype. The association of voxel density reduction and ageing is consistent with observations of a subgroup of older pre-mutation males who present with cognitive decline. Moreover, our findings suggest, for the first time, an association between voxel density reduction and genetic variation in FraX.

Adolescent↗

PubMed2004

Paternal transmission of fragile X syndrome.

We present a family in which a fragile X mosaic male, who carries both premutation and full mutation alleles in his peripheral blood leukocytes, has a daughter with both premutation and partially methylated full mutation alleles and a significant developmental disability. To our knowledge, this is the first report of such an occurrence and it challenges current thinking about the expansion and transmission of unstable FMR1 alleles from men to their daughters. It is currently accepted that neither males with premutations nor full mutations are at risk for having daughters with full mutations and fragile X syndrome. The sperm cells of full mutation males are thought to carry only premutation alleles. These alleles, when transmitted through a male, regardless of his cognitive status, are thought to be unable to expand to full mutations in the next generation. In effect, the expansion from premutation to full mutation has only been observed through female meioses. The sperm cells in the father in this family have been shown to contain only alleles in the premutation range. Since his daughter has both premutation and full mutation alleles the expansion to full mutation in this case must have occurred postzygotically.

Alleles↗

PubMed2004

FMR1 RNA within the intranuclear inclusions of fragile X-associated tremor/ataxia syndrome (FXTAS).

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a recently identified neurodegenerative disorder affecting older adult males with premutation alleles of the fragile X mental retardation 1 (FMR1) gene. The principal clinical features of FXTAS include progressive intention tremor, gait ataxia, parkinsonism, and autonomic dysfunction. The disorder affects at least one-third of carrier males over 50 years of age and, with an estimated carrier frequency of approximately 1/800 males, is likely to be one of the most common heritable forms of tremor and ataxia among older adult males in the general population. Brains from all FXTAS cases examined to date (10/10) possess numerous ubiquitin-positive intranuclear inclusions in broad distribution throughout the cerebrum and brainstem. The absence of either the neurodegenerative disorder or inclusions among adults with fragile X syndrome (who lack the FMR1 protein), coupled with elevated FMR1 mRNA with expanded CGG repeats in premutation carriers, has led us to propose an RNA toxic gain-of-function model for FXTAS. Consistent with this model, we have now identified FMR1 mRNA within the intranuclear inclusions isolated from post-mortem (FXTAS) brain tissue.

Aged↗

PubMed2004

Penetrance of the fragile X-associated tremor/ataxia syndrome in a premutation carrier population.

CONTEXT: Premutation expansions (55-200 CGG repeats) of the fragile X mental retardation 1 (FMR1) gene are frequent in the general population, with estimated prevalences of 1 per 259 females and 1 per 813 males. Several articles have recently described the presence of late-onset neurological symptoms in male carriers of premutation (FMR1) alleles. The main clinical features described in this newly identified syndrome are cerebellar ataxia and intention tremor. Additional documented symptoms include short-term memory loss, executive functional deficits, cognitive decline, parkinsonism, peripheral neuropathy, lower-limb proximal muscle weakness, and autonomic dysfunction. OBJECTIVE: To study the penetrance of the fragile X-associated tremor/ataxia syndrome (FXTAS) among premutation carriers. DESIGN, SETTING, AND PARTICIPANTS: Family-based study of 192 individuals (premutation carriers and controls) whose families belong to the Northern or Southern California Fragile X Associations. Data were collected (March 2002-April 2003) through a survey and a standardized neurological examination, which was videotaped and subsequently scored in a blinded fashion. MAIN OUTCOME MEASURES: Penetrance of intention tremor and ataxia among adult carriers (aged > or =50 years) of premutation expansions of the FMR1 gene. RESULTS: Data from the survey of 192 individuals demonstrated an age-related penetrance of the combination of reported intention tremor and gait ataxia in male carriers (17%, 38%, 47%, and 75% [lower-bound estimates] for participants aged 50-59, 60-69, 70-79, and > or =80 years, respectively). The male carrier group had an age-adjusted 13-fold increased risk (95% confidence interval, 3.9-25.4; P =.003) of combined intention tremor and gait ataxia when compared with male controls. The clinical examination data from 93 individuals demonstrated that male carriers experienced more difficulties on each of 3 standardized neurological rating scales compared with controls (P<.05). Female carrier scores were also higher than those of female controls (P<.05) on 2 of the 3 neurological rating scales, but no participant was identified with probable or definite FXTAS. CONCLUSIONS: The study demonstrates that older male carriers of premutation alleles of the FMR1 gene are at high risk of developing FXTAS. Since male premutation carriers are relatively common in the general population, older men with ataxia and intention tremor should be screened for the FMR1 mutation, especially if these signs are accompanied by parkinsonism, autonomic dysfunction, or cognitive decline, regardless of family history.

Aged↗

PubMed2004

Redistribution of transcription start sites within the FMR1 promoter region with expansion of the downstream CGG-repeat element.

Fragile X syndrome, the most common form of mental impairment, is caused by expansion of a (CGG)n trinucleotide repeat element located in the 5' untranslated region of the fragile X mental retardation 1 (FMR1) gene. Repeat expansion is known to influence both transcription and translation; however, the mechanisms by which the CGG element exerts its effects are not known. In the current work, we have utilized 5'-RLM-RACE to examine the influence of CGG repeat number on the utilization of transcription start sites in normal (n<55) and premutation (54<n<200) cell lines of both non-neural (lymphoblastoid) and neural (primary astrocyte) origin. Our results demonstrate that, in both neural and non-neural cells, transcription of the FMR1 gene is initiated from several transcription start sites within a approximately 50 nt region that lies approximately 130 nt upstream of the CGG repeat element. For normal alleles, most transcripts initiate from the downstream-most start site, close to the single position identified previously. Surprisingly, as the size of the CGG repeat expands into the premutation range, initiation shifts to the upstream sites, suggesting that the CGG element may act as a downstream enhancer/modulator of transcription. The shift in start site selection for both neural and non-neural cells indicates that the effect is general. Furthermore, the correspondence between start site utilization and the degree of elevation of FMR1 mRNA suggests that a substantial fraction of the increased message in the premutation range may derive from the upstream start sites.

Base Sequence↗

PubMed2004

Screen for expanded FMR1 alleles in patients with essential tremor.

Fragile X-associated tremor/ataxia syndrome (FXTAS), a neurodegenerative disorder, was described recently among male carriers of expanded alleles (55-200 CGG repeats; premutation range) of the fragile X mental retardation 1 (FMR1) gene. Major features of the syndrome include intention tremor, gait ataxia, and parkinsonism in men over 50 years of age. This disorder is believed to be relatively common, possibly affecting 1 in 3,000 men over the age of 50 years in the general population. This raises the possibility that some patients presenting with essential tremor (ET) may harbor expanded FMR1 alleles. We screened 81 ET patients (40 males, 41 females) for expanded FMR1 alleles to determine whether ET is associated with such alleles. None of the ET cases had the premutation genotype. CGG repeat sizes ranged from 5 to 47 repeats within this study population, suggesting that expanded FMR1 alleles are uncommon among patients with ET. Screening of movement disorder patients with other clinical features of FXTAS (e.g., ataxia and parkinsonism) may be more likely to yield expanded FMR1 alleles.

Aged↗

PubMed2004

A neuropsychological investigation of male premutation carriers of fragile X syndrome.

It is currently thought that fragile X syndrome (FraX; the most common inherited form of learning disability) results from having more than 200 cytosine-guanine-guanine (CGG) trinucleotide repeats, with consequent methylation of the fragile X mental retardation (FMR1) gene and loss of FMR1 protein (FMRP). It was also considered that premutation carriers (with 55-200 CGG repeats) are unaffected, although a tremor/ataxia syndrome has recently been described in older adult male carriers. We reported that premutation expansion of CGG trinucleotide repeats affects brain anatomy, which, together with other studies, indicates that the molecular model for FraX needs modification. However, there are few studies on the cognitive ability of adult male premutation carriers. Thus, we selected 20 male premutation carriers on the basis of their genetic phenotype, and compared them to 20 male controls matched on age, IQ and handedness. We investigated intellectual functioning, executive function, memory, attention, visual and spatial perception, and language and pragmatics. The premutation carriers had significant impairments on tests of executive function (Verbal Fluency, Trail Making Test and Tower of London) and memory (Names sub-test of the Doors and People, Verbal Paired Associates Immediate Recall and Visual Paired Associates Delayed Recall sub-tests of the WMS-R, and Category Fluency Test for natural kinds). We therefore suggest that CGG trinucleotide repeats in the premutation range affect specific neuronal circuits that are concordant with specific neuropsychological deficits; and that these deficits reflect an emerging neuropsychological phenotype of premutation FraX.

Adult↗

PubMed2004

Autistic spectrum disorder and the fragile X premutation.

Fragile X syndrome (FXS) is the most common inherited cause of mental retardation. It is also one of the most common identifiable causes of Autism Spectrum Disorder (ASD). Carriers of FXS are often considered to be cognitively and behaviorally unaffected. However, we report here on six individuals in the premutation range who also have ASD. A comparison is made with five subjects in the premutation range who did not receive a diagnosis of ASD. The six individuals with ASD had a range of cognitive ability levels from no impairment to moderate retardation. Discussion includes the impact of molecular variables including lowered FMR1 protein and elevated FMR1 mRNA in addition to environmental factors leading to the complex neurodevelopmental disorder of ASD.

Adult↗

PubMed2003

The (CGG)n repeat element within the 5' untranslated region of the FMR1 message provides both positive and negative cis effects on in vivo translation of a downstream reporter.

The human fragile X mental retardation 1 (FMR1) gene contains a polymorphic (CGG) trinucleotide repeat element in its 5' untranslated region. Expansion of the (CGG)n element beyond 200 repeats (full mutation range) generally leads to transcriptional silencing; consequent loss of the FMR1 protein (FMRP) results in fragile X syndrome, the most frequent form of inherited mental impairment. For carriers of smaller expansions (55< or =n< or =200; premutation range), FMRP levels are gradually reduced with increasing repeat number, despite elevated FMR1 mRNA levels, suggesting that translation is impeded within the premutation range. To examine in more detail the influence of the CGG repeat on translation, CMV immediate-early promoter constructs, containing the FMR1 5'-UTR with various (CGG)n repeat lengths (0< or =n< or =99) and a downstream (luciferase) reporter, were transfected into two human cell lines, a neural cell-derived line (SK) and a fetal kidney cell-derived line (293). For both cell types, the CGG element exerts distinct effects on reporter expression, depending on the length of the repeat. For n> or =30, luciferase expression decreases with increasing repeat length, consistent with earlier observations of decreased FMRP expression in peripheral blood leucocytes over the same repeat range, despite a slight increase in mRNA level for the larger repeats. Surprisingly, for smaller alleles (0< or =n< or =30), reporter expression actually increases by nearly two-fold with increasing repeat length in the absence of any change in mRNA level. These results suggest that the CGG repeat element can exert both positive (n<30) and negative (n>30) effects on translation. Interestingly, optimal translation appears to occur near the modal repeat number within the general human population.

5' Untranslated Regions↗

PubMed2003

The FMR1 CGG repeat mouse displays ubiquitin-positive intranuclear neuronal inclusions; implications for the cerebellar tremor/ataxia syndrome.

Recent studies have reported that alleles in the premutation range in the FMR1 gene in males result in increased FMR1 mRNA levels and at the same time mildly reduced FMR1 protein levels. Some elderly males with premutations exhibit an unique neurodegenerative syndrome characterized by progressive intention tremor and ataxia. We describe neurohistological, biochemical and molecular studies of the brains of mice with an expanded CGG repeat and report elevated Fmr1 mRNA levels and intranuclear inclusions with ubiquitin, Hsp40 and the 20S catalytic core complex of the proteasome as constituents. An increase was observed of both the number and the size of the inclusions during the course of life, which correlates with the progressive character of the cerebellar tremor/ataxia syndrome in humans. The observations in expanded-repeat mice support a direct role of the Fmr1 gene, by either CGG expansion per se or by mRNA level, in the formation of the inclusions and suggest a correlation between the presence of intranuclear inclusions in distinct regions of the brain and the clinical features in symptomatic premutation carriers. This mouse model will facilitate the possibilities to perform studies at the molecular level from onset of symptoms until the final stage of the disease.

Animals↗

PubMed2003

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.

Aged↗

PubMed2003

The fragile X premutation presenting as essential tremor.

CONTEXT: The fragile X premutation has recently been reported to be associated with a neurodegenerative syndrome, chiefly characterized by intention tremor, gait ataxia, and executive cognitive deficits in men older than 50 years. Essential tremor is a frequent cause of tremor in elderly patients and in some cases is associated with impaired tandem gait and cognitive deficits. OBJECTIVE: To describe 2 fragile X carriers whose clinical presentation mimicked essential tremor. DESIGN: The 2 patients described herein underwent neurologic examinations by experienced movement disorders neurologists, magnetic resonance imaging, and fragile X gene, messenger RNA, and protein analyses. One underwent detailed neuropsychological testing. SETTING: Patients were studied at 2 large university movement disorders clinics. PATIENTS: Both patients were white men older than 50 years who had been diagnosed as having essential tremor and then found to be fragile X carriers. RESULTS: Besides disabling intention tremor, the 2 patients had impaired tandem, generalized brain atrophy, and unusual bilateral T2 middle cerebellar hyperintensities on magnetic resonance imaging. The patient who underwent neuropsychological testing had frontal executive deficits. Both patients had elevated fragile X mental retardation gene 1 messenger RNA and reduced fragile X mental retardation 1 protein levels. CONCLUSION: The fragile X carrier state may underlie the clinical findings in some older men diagnosed as having essential tremor.

Aged↗

PubMed2002

Reduced FMR1 mRNA translation efficiency in fragile X patients with premutations.

The Fragile X mental retardation gene (FMR1) contains a polymorphic trinucleotide CGG repeat in the 5' untranslated region (UTR) of the FMR1 messenger. We have characterized three lymphoblastoid cell lines derived from unrelated male carriers of a premutation that overexpress FMR1 mRNA and show reduced FMRP level compared to normal cells. The analysis of polysomes/mRNPs distribution of mRNA in the cell lines with a premutation shows that the polysomal association of FMR1 mRNA, which is high in normal cells, becomes progressively lower with increasing CGG repeat expansion. In addition, we could detect a very low level of FMR1 mRNA in a lymphoblastoid cell line from a patient with a full mutation. In this case, FMR1 mRNA is not at all associated with polysomes, in agreement with the complete absence of FMRP. The impairment of FMR1 mRNA translation in patients with the Fragile X syndrome with FMR1 premutation is the cause of the lower FMRP levels that leads to the clinical involvement.

Cell Line↗

PubMedDate not supplied

Fragile X premutation carriers: characteristic MR imaging findings of adult male patients with progressive cerebellar and cognitive dysfunction.

BACKGROUND AND PURPOSE: Our purpose was to characterize the findings of MR imaging of the brain of adult male fragile X premutation carriers with a recently identified disorder characterized by ataxia, tremor, rigidity, and cognitive dysfunction. METHODS: MR imaging studies of the brain of 17 male patients were characterized for signal intensity and for size of ventricles, cerebral and cerebellar sulci, and brain stem. Comparison was made with age- and sex-matched control participants. Southern blot and/or polymerase chain reaction methods were used to analyze CGG trinucleotide repeats in the fragile X mental retardation 1 gene. RESULTS: Fifteen of 17 patients showed symmetrically decreased T1 and increased T2 signal intensity in cerebellar white matter lateral, superior, and inferior to the dentate nuclei. Fourteen of 17 had similar signal intensity alterations in the middle cerebellar peduncles. Cerebellar cortical atrophy was present in 16 of 17 and cerebral atrophy in 17 of 17. Evan's Index as a measure of ventricular size averaged 0.35 (range, 0.25-0.46), with that for age-matched control participants averaging 0.28 (range, 0.24-0.31) (P <.005). The mean third ventricle width was 11 mm (for control participants, 6 mm; P <.01). Corpus callosum was thinned in 14 of 16 participants. Middle cerebellar peduncles were atrophic when compared with those of control participants (P <.005). Pontine transverse dimension was 25 mm (for control participants, 31 mm; P <.005), and rostral-caudal length averaged 26 mm (for control participants, 29 mm; P <.005). CGG repeats clustered in the low to mid premutation range (86 +/- 10 CGG repeats) in the 17 patients. CONCLUSION: MR imaging findings in symptomatic male fragile X premutation carriers are characteristic of this disorder. Recognition of these alterations may support a specific diagnosis and may have implications for the potential occurrence of fragile X syndrome in the children of reproductive age female relatives.

Aged↗