GAA Allele Research Articles

Differential Gene Expression in Late-Onset Friedreich Ataxia: A Comparative Transcriptomic Analysis Between Symptomatic and Asymptomatic Sisters.

Friedreich ataxia (FRDA) is the most common inherited ataxia, primarily impacting the nervous system and the heart. It is characterized by GAA repeat expansion in the FXN gene, leading to reduced mitochondrial frataxin levels. Previously, we described a family displaying two expanded GAA alleles, not only in the proband affected by late-onset FRDA but also in the younger asymptomatic sister. The molecular characterization of the expanded repeats showed that the affected sister carried two canonical uninterrupted GAA expended repeats, whereas the asymptomatic sister had a compound heterozygous for a canonical GAA repeat and an expanded GAAGGA motif. Therefore, we decided to perform RNA sequencing (RNA-seq) on fibroblasts from both sisters in order to understand whether some genes and/or pathways might be differently involved in the occurrence of FRDA clinical manifestation. The transcriptomic analysis revealed 398 differentially expressed genes. Notably, TLR4, IL20RB, and SLITRK5 were up-regulated, while TCF21 and GRIN2A were down-regulated, as validated by qRT-PCR. Gene ontology (GO) enrichment and network analysis highlighted significant involvement in immune response and neuronal functions. Our results, in particular, suggest that TLR4 may contribute to inflammation in FRDA, while IL20RB, SLITRK5, TCF21, and GRIN2A dysregulation may play roles in the disease pathogenesis. This study introduces new perspectives on the inflammatory and developmental aspects in FRDA, offering potential targets for therapeutic intervention.

Nuclear Factor Erythroid 2-Related Factor 2 Activation Might Mitigate Clinical Symptoms in Friedreich's Ataxia: Clues of an "Out-Brain Origin" of the Disease From a Family Study.

Friedreich’s ataxia (FRDA) is the most frequent autosomal recessive ataxia in western countries, with a mean age of onset at 10–15 years. Patients manifest progressive cerebellar and sensory ataxia, dysarthria, lower limb pyramidal weakness, and other systemic manifestations. Previously, we described a family displaying two expanded GAA alleles not only in the proband affected by late-onset FRDA but also in the two asymptomatic family members: the mother and the younger sister. Both of them showed a significant reduction of frataxin levels, without any disease manifestation. Here, we analyzed if a protective mechanism might contribute to modulate the phenotype in this family. We particularly focused on the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2), the first line of antioxidant defense in cells, and on the glutathione (GSH) system, an index of reactive oxygen species (ROS) detoxification ability. Our findings show a great reactivity of the GSH system to the frataxin deficiency, particularly in the asymptomatic mother, where the genes of GSH synthesis [glutamate–cysteine ligase (GCL)] and GSSG detoxification [GSH S-reductase (GSR)] were highly responsive. The GSR was activated even in the asymptomatic sister and in the proband, reflecting the need of buffering the GSSG increase. Furthermore, and contrasting the NRF2 expression documented in FRDA tissues, NRF2 was highly activated in the mother and in the younger sister, while it was constitutively low in the proband. This suggests that, also under frataxin depletion, the endogenous stimulation of NRF2 in asymptomatic FRDA subjects may contribute to protect against the progressive oxidative damage, helping to prevent the onset of neurological symptoms and highlighting an “out-brain origin” of the disease.

Methylated and unmethylated epialleles support variegated epigenetic silencing in Friedreich ataxia.

Friedreich ataxia (FRDA) is typically caused by homozygosity for an expanded GAA triplet-repeat in intron 1 of the FXN gene, which results in transcriptional deficiency via epigenetic silencing. Most patients are homozygous for alleles containing > 500 triplets, but a subset (~20%) have at least one expanded allele with < 500 triplets and a distinctly milder phenotype. We show that in FRDA DNA methylation spreads upstream from the expanded repeat, further than previously recognized, and establishes an FRDA-specific region of hypermethylation in intron 1 (~90% in FRDA versus < 10% in non-FRDA) as a novel epigenetic signature. The hypermethylation of this differentially methylated region (FRDA-DMR) was observed in a variety of patient-derived cells; it significantly correlated with FXN transcriptional deficiency and age of onset, and it reverted to the non-disease state in isogenically corrected induced pluripotent stem cell (iPSC)-derived neurons. Bisulfite deep sequencing of the FRDA-DMR in peripheral blood mononuclear cells from 73 FRDA patients revealed considerable intra-individual epiallelic variability, including fully methylated, partially methylated, and unmethylated epialleles. Although unmethylated epialleles were rare (median = 0.33%) in typical patients homozygous for long GAA alleles with > 500 triplets, a significantly higher prevalence of unmethylated epialleles (median = 9.8%) was observed in patients with at least one allele containing < 500 triplets, less severe FXN deficiency (>20%) and later onset (>15 years). The higher prevalence in mild FRDA of somatic FXN epialleles devoid of DNA methylation is consistent with variegated epigenetic silencing mediated by expanded triplet-repeats. The proportion of unsilenced somatic FXN genes is an unrecognized phenotypic determinant in FRDA and has implications for the deployment of effective therapies.

Frequency and Genetic Profile of Compound Heterozygous Friedreich’s Ataxia Patients—the Brazilian Experience

Friedreich ataxia (FRDA) is the most common autosomal recessive ataxia in Caucasian populations. It is caused by a homozygous GAA expansion in the first intron of the frataxin gene (FXN) (OMIM: 606829) in 96% of the affected individuals. The remaining patients have a GAA expansion in one allele and a point mutation in the other. Little is known about compound heterozygous patients outside Europe and North America. We have thus designed a study to determine the frequency and mutational profile of these patients in Brazil. To accomplish that, we recruited all patients with ataxia and at least one expanded GAA allele at FXN from 3 national reference centers. We identified those subjects with a single expansion and proceeded with further genetic testing (Sanger sequencing and CGH arrays) for those. There were 143 unrelated patients (128 families), five of which had a single expanded allele. We identified point mutations in three out of these five (3/128 = 2.34%). Two patients had the c.157delC variant, whereas one individual had the novel variant c.482+1G>T. These results indicate that FXN point mutations are rare, but exist in Brazilian patients with FRDA. This has obvious implications for diagnostic testing and genetic counseling.

Effects of a higher dose of alglucosidase alfa on ventilator-free survival and motor outcome in classic infantile Pompe disease: an open-label single-center study.

BackgroundThough enzyme-replacement therapy (ERT) with alglucosidase alfa has significantly improved the prospects for patients with classic infantile Pompe disease, some 50 % of treated infants do not survive ventilator-free beyond the age of 3 years. We investigated whether higher and more frequent dosing of alglucosidase alfa improves outcome.MethodsEight cross-reactive immunological material (CRIM) positive patients were included in the study. All had fully deleterious mutations in both GAA alleles. Four received a dose of 20 mg/kg every other week (eow) and four received 40 mg/kg/week. Survival, ventilator-free survival, left-ventricular mass index (LVMI), motor outcome, infusion-associated reactions (IARs), and antibody formation were evaluated.ResultsAll eight patients were alive at study end, seven of them remained ventilator-free. The patient who became ventilator dependent was treated with 20 mg/kg eow. Three of the four patients receiving 20 mg/kg eow learned to walk; two of them maintained this ability at study end. All four patients receiving 40 mg/kg/week acquired and maintained the ability to walk at study end (ages of 3.3–5.6 years), even though their baseline motor functioning was poorer. There were no apparent differences between the two dose groups with respect to the effect of ERT on LVMI, the number of IARs and antibody formation.ConclusionsOur data may suggest that a dose of 40 mg/kg/week improves outcome of CRIM positive patients over that brought by the currently recommended dose of 20 mg/kg eow. Larger studies are needed to draw definite conclusions.

Friedreich Ataxia: Executive Control Is Related to Disease Onset and GAA Repeat Length

Friedreich ataxia (FRDA) is the most frequent inherited ataxia. Neuropsychological studies suggest that FRDA may be associated with specific cognitive impairment. Very little is known about the relation between cognitive performance, demographics and disease-related parameters, such as GAA repeat size, age of onset and disease duration. The present investigation aimed at assessing cognitive functions in a representative sample of FRDA patients and at identifying the most relevant disease-related parameters. Twenty-nine adult FRDA patients underwent neuropsychological tests assessing executive functions, attention, memory and visual perception. Performance was compared with 28 age- and education-matched controls as well as with standardized norms. The relation between neuropsychological outcome, demographical variables and disease-related parameters was assessed. Cognitive impairment affected only a subgroup of patients and mostly concerned attentional and executive functions. Good cognitive performance was associated with a later disease onset, shorter GAA repeat length and lower burden of disease. Age at disease onset has been found to be a good predictor when a cut-off of 14years was chosen. No correlation was found between cognitive performance and education, age or disease duration. The present study extends earlier findings in FRDA showing that performance in attentional and executive function tasks is best predicted by the age at disease onset. Moreover, executive functions show a clear relationship to disease severity and repeat size of the shorter GAA allele. These findings therefore have important implications for patient counselling regarding education and career choices.

Neurons and cardiomyocytes derived from induced pluripotent stem cells as a model for mitochondrial defects in Friedreich's ataxia

SUMMARYFriedreich’s ataxia (FRDA) is a recessive neurodegenerative disorder commonly associated with hypertrophic cardiomyopathy. FRDA is due to expanded GAA repeats within the first intron of the gene encoding frataxin, a conserved mitochondrial protein involved in iron-sulphur cluster biosynthesis. This mutation leads to partial gene silencing and substantial reduction of the frataxin level. To overcome limitations of current cellular models of FRDA, we derived induced pluripotent stem cells (iPSCs) from two FRDA patients and successfully differentiated them into neurons and cardiomyocytes, two affected cell types in FRDA. All FRDA iPSC lines displayed expanded GAA alleles prone to high instability and decreased levels of frataxin, but no biochemical phenotype was observed. Interestingly, both FRDA iPSC-derived neurons and cardiomyocytes exhibited signs of impaired mitochondrial function, with decreased mitochondrial membrane potential and progressive mitochondrial degeneration, respectively. Our data show for the first time that FRDA iPSCs and their neuronal and cardiac derivatives represent promising models for the study of mitochondrial damage and GAA expansion instability in FRDA.

Clinical use of frataxin measurement in a patient with a novel deletion in the FXN gene

Friedreich ataxia (FRDA) is caused by a GAA expansion in the first intron of the FXN gene, which encodes frataxin. Four percent of patients harbor a point mutation on one allele and a GAA expansion on the other. We studied an Italian patient presenting with symptoms suggestive of FRDA, and carrying a single expanded 850 GAA allele. As a second diagnostic step, frataxin was measured in peripheral blood mononuclear cells, and proved to be in the pathological range (2.95 pg/μg total protein, 12.7 % of control levels). Subsequent sequencing revealed a novel deletion in exon 5a (c.572delC) which predicted a frameshift at codon 191 and a premature truncation of the protein at codon 194 (p.T191IfsX194). FXN/mRNA expression was reduced to 69.2 % of control levels. Clinical phenotype was atypical with absent dysarthria, and rapid disease progression. L-Buthionine-sulphoximine treatment of the proband's lymphoblasts showed a severe phenotype as compared to classic FRDA.

The genotype–phenotype correlation in Pompe disease

Pompe disease is an autosomal recessive lysosomal glycogen storage disorder that is caused by acid α-glucosidase (GAA) deficiency and is due to pathogenic sequence variations in the corresponding GAA gene. The correlation between genotypes and phenotypes is strict, in that patients with the most severe phenotype, classic infantile Pompe disease, have two pathogenic mutations, one in each GAA allele, that prevent the formation of GAA or totally obliterates its function. All patients with less progressive phenotypes have at least one sequence variation that allows normal or low level synthesis of GAA leading to the formation of analytically measurable, low level GAA activity in most cases. There is an overall trend of finding higher GAA enzyme levels in patients with onset of symptoms in adulthood when compared to patients who show clinical manifestations in early childhood, aged 0-5 years, with a rapidly progressive course, but who lack the severe characteristics of classic infantile Pompe disease. However, several cases have been reported of adult-onset disease with very low GAA activity, which in all those cases corresponds with the GAA genotype. The clinical diversity observed within a large group of patients with functionally the same GAA genotype and the same c.-32-13C > T haplotype demonstrates that modifying factors can have a substantial effect on the clinical course of Pompe disease, disturbing the GAA genotype-phenotype correlation. The present day challenge is to identify these factors and explore them as therapeutic targets.

P3.59 Remarkably low acid alpha-glucosidase activity in two patients with adult-onset Pompe disease

Pompe disease in adults usually presents as a limb-girdle myopathy and is caused by pathogenic mutations in the GAA-gene. The majority of the adult patients have the c.-32-13T>G mutation in 1 GAA allele, resulting in residual enzyme activity, and a fully deleterious mutation in the other. In the Dutch population the activity of acid alpha-glucosidase in these patients ranges from 7.3 to 19.9nmol/mg.h. We present 2 adult patients that don’t have the common c.-32-13T>G/ null genotype, but novel pathogenic mutations that encode much lower enzyme activity.

Predictors of progression in patients with Friedreich ataxia

Friedreich ataxia is an inherited, progressive, neurodegenerative disorder that is clinically heterogeneous. It is caused by a trinucleotide (GAA) repeat expansion resulting in frataxin loss and oxidative stress. We assessed clinical features including the development of cardiomyopathy and scoliosis and disease progression including loss of ambulation and interference with activities of daily living relative to the length of the GAA repeat, age of onset, and age of diagnosis in a retrospective cohort study of 61 genetically confirmed patients. The use of antioxidants such as vitamins, dietary supplements, and idebenone was also examined. Linear regression and Cox proportional hazard models assessed predictors to disease milestones. The shorter GAA allele accounted for part of the variability in the age of diagnosis (46%) and less in the age of onset (27%). Multivariate analysis demonstrated that age at diagnosis, which may incorporate other genetic and environmental factors, is more important than GAA length in predicting cardiomyopathy, scoliosis, and disease progression.

P.[G576S; E689K]: pathogenic combination or polymorphism in Pompe disease?

We discuss four cases of acid alpha-glucosidase deficiency (EC, 3.2.1.3/20) without evident symptoms of Pompe disease (OMIM No 232300) in individuals of Asian descent. In three cases, the deficiency was associated with homozygosity for the sequence variant c.[1726G>A; 2065G>A] in the acid alpha-glucosidase gene (GAA) translating into p.[G576S; E689K]. One of these cases was a patient with profound muscular atrophy, another had cardio-myopathy and the third had no symptoms. The fourth case, the mother of a child with Pompe disease, was compound heterozygote for the GAA sequence variants c.[1726G>A; 2065G>A]/c.2338G>A (p.W746X) and had no symptoms either. Further investigations revealed that c.[1726A; 2065A] is a common GAA allele in the Japanese and Chinese populations. Our limited study predicts that approximately 4% of individuals in these populations are homozygote c.[1726A; 2065A]. The height of this figure in contrast to the rarity of Pompe disease in Asian populations and the clinical history of the cases described in this paper virtually exclude that homozygosity for c.[1726A; 2065A] causes Pompe disease. As c.[1726A; 2065A] homozygotes have been observed with similarly low acid alpha-glucosidase activity as some patients with Pompe disease, we caution they may present as false positives in newborn screening programs especially in Asian populations.

Extension of the mutation spectrum in Friedreich's ataxia: detection of an exon deletion and novel missense mutations.

Friedreich's ataxia (FRDA), the most common autosomal recessively inherited ataxia, is due to a homozygous GAA triplet repeat expansion in the first intron of the FRDA gene in about 96% of patients. Approximately 4% of FRDA patients are compound heterozygotes with a GAA repeat expansion in one allele and a point mutation in the coding region of the second allele. To reinvestigate the mutation spectrum, we searched for mutations including exon deletions in six patients heterozygous for the GAA repeat expansion and found two unknown missense mutations, p.Asn146Lys and p.Leu186Arg, in trans to the expanded FRDA allele. Interestingly, we detected a heterozygous 2776 bp deletion including exon 5a in one of our patients. This deletion removes 50 of the 210 residues of the frataxin. Furthermore, since no FRDA case with two-point mutations is known, we screened eight patients with FRDA phenotype but GAA alleles within the normal range but did not reveal a mutation within the FRDA gene. In addition, DNA polymorphisms have been found in four out of 100 control individuals in this study.

Twenty-two novel mutations in the lysosomal alpha-glucosidase gene (GAA) underscore the genotype-phenotype correlation in glycogen storage disease type II.

Patients with glycogen storage disease type II (GSDII, Pompe disease) suffer from progressive muscle weakness due to acid alpha-glucosidase deficiency. The disease is inherited as an autosomal recessive trait with a spectrum of clinical phenotypes. We have investigated 29 cases of GSDII and thereby identified 55 pathogenic mutations of the acid alpha-glucosidase gene (GAA) encoding acid maltase. There were 34 different mutations identified, 22 of which were novel. All of the missense mutations and two other mutations with an unpredictable effect on acid alpha-glucosidase synthesis and function were transiently expressed in COS cells. The effect of a novel splice-site mutation was investigated by real-time PCR analysis. The outcome of our analysis underscores the notion that the clinical phenotype of GSDII is largely dictated by the nature of the mutations in the GAA alleles. This genotype-phenotype correlation makes DNA analysis a valuable tool to help predict the clinical course of the disease.

Genotype and phenotype analysis of Friedreich's ataxia compound heterozygous patients.

Friedreich's ataxia is caused by mutations in the FRDA gene that encodes frataxin, a nuclear-encoded mitochondrial protein. Most patients are homozygous for the expansion of a GAA triplet repeat within the FRDA gene, but a few patients show compound heterozygosity for a point mutation and the GAA-repeat expansion. We analyzed DNA samples from a cohort of 241 patients with autosomal recessive or isolated spinocerebellar ataxia for the GAA triplet expansion. Patients heterozygous for the GAA expansion were screened for point mutations within the FRDA coding region. Molecular analyses included the single-strand conformation polymorphism analysis, direct sequencing, and linkage analysis with FRDA locus flanking markers. Seven compound heterozygous patients were identified. In four patients, a point mutation that predicts a truncated frataxin was detected. Three of them associated classic early-onset Friedreich's ataxia with an expanded GAA allele greater than 800 repeats. The other patient associated late-onset disease at the age of 29 years with a 350-GAA repeat expansion. In two patients manifesting the classical phenotype, no changes were observed by single-strand conformation polymorphism (SSCP) analysis. Linkage analysis in a family with two children affected by an ataxic syndrome, one of them showing heterozygosity for the GAA expansion, confirmed no linkage to the FRDA locus. Most point mutations in compound heterozygous Friedreich's ataxia patients are null mutations. In the present patients, clinical phenotype seems to be related to the GAA repeat number in the expanded allele. Complete molecular definition in these patients is required for clinical diagnosis and genetic counseling.