Specific Biomarkers in Spinocerebellar Ataxia Type 3: A Systematic Review of Their Potential Uses in Disease Staging and Treatment Assessment.

Spinocerebellar ataxia type 3 (SCA3) is the most common type of disease related to poly-glutamine (polyQ) repeats. Its hallmark pathology is related to the abnormal accumulation of ataxin 3 with a longer polyQ tract (polyQ-ATXN3). However, there are other mechanisms related to SCA3 progression that require identifying trait and state biomarkers for a more accurate diagnosis and prognosis. Moreover, the identification of potential pharmacodynamic targets and assessment of therapeutic efficacy necessitates valid biomarker profiles. The aim of this review was to identify potential trait and state biomarkers and their potential value in clinical trials. Our results show that, in SCA3, there are different fluid biomarkers involved in neurodegeneration, oxidative stress, metabolism, miRNA and novel genes. However, neurofilament light chain NfL and polyQ-ATXN3 stand out as the most prevalent in body fluids and SCA3 stages. A heterogeneity analysis of NfL revealed that it may be a valuable state biomarker, particularly when measured in plasma. Nonetheless, since it could be a more beneficial approach to tracking SCA3 progression and clinical trial efficacy, it is more convenient to perform a biomarker profile evaluation than to rely on only one.

Machado Joseph-Disease Is Rare in the Peruvian Population.

Spinocerebellar ataxia type 3 or Machado-Joseph disease (MJD/SCA3) is the most prevalent autosomal dominant cerebellar ataxia worldwide, but its frequency varies by geographic region. We describe MJD/SCA3 patients diagnosed in a tertiary healthcare institution in Peru. In a cohort of 341 individuals (253 probands) with clinical ataxia diagnosis, seven MJD/SCA3 probands were identified and their pedigrees extended, detecting a total of 18 MJD/SCA3 cases. Out of 506 alleles from all probands from this cohort, the 23-CAG repeat was the most common ATXN3 allele (31.8%), followed by the 14-CAG repeat allele (26.1%). Normal alleles ranged from 12 to 38 repeats while pathogenic alleles ranged from 64 to 75 repeats. We identified 80 large normal (LN) alleles (15.8%). Five out of seven families declared an affected family member traced back to foreign countries (England, Japan, China, and Trinidad and Tobago). MJD/SCA3 patients showed ataxia, accompanied by pyramidal signs, dysarthria, and dysphagia as well as abnormal oculomotor movements. In conclusion, ATXN3 allelic distribution in non-MJD/SCA3 patients with ataxia is similar to the distribution in normal individuals around the world, whereas LN allele frequency reinforces no correlation with the frequency of MJD/SCA3. Evidence of any atypical MJD/SCA3 phenotype was not found. Furthermore, haplotypes are required to confirm the foreign origin of MJD/SCA3 in the Peruvian population.

CAG Repeat Size Influences the Progression Rate of Spinocerebellar Ataxia Type 3.

OBJECTIVE: In spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD), the expanded cytosine adenine guanine (CAG) repeat in ATXN3 is the causal mutation, and its length is the main factor in determining the age at onset (AO) of clinical symptoms. However, the contribution of the expanded CAG repeat length to the rate of disease progression after onset has remained a matter of debate, even though an understanding of this factor is crucial for experimental data on disease modifiers and their translation to clinical trials and their design. METHODS: Eighty-two Dutch patients with SCA3/MJD were evaluated annually for 15 years using the International Cooperative Ataxia Rating Scale (ICARS). Using linear growth curve models, ICARS progression rates were calculated and tested for their relation to the length of the CAG repeat expansion and to the residual age at onset (RAO): The difference between the observed AO and the AO predicted on the basis of the CAG repeat length. RESULTS: On average, ICARS scores increased 2.57 points/year of disease. The length of the CAG repeat was positively correlated with a more rapid ICARS progression, explaining 30% of the differences between patients. Combining both the length of the CAG repeat and RAO as comodifiers explained up to 47% of the interpatient variation in ICARS progression. INTERPRETATION: Our data imply that the length of the expanded CAG repeat in ATXN3 is a major determinant of clinical decline, which suggests that CAG-dependent molecular mechanisms similar to those responsible for disease onset also contribute to the rate of disease progression in SCA3/MJD. ANN NEUROL 2021;89:66-73.

Selective forces acting on spinocerebellar ataxia type 3/Machado-Joseph disease recurrency: A systematic review and meta-analysis.

Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is a dominant neurodegenerative disease caused by the expansion of a CAG repeat tract in ATXN3. Anticipation and worsening of clinical picture in subsequent generations were repeatedly reported, but there is no indication that SCA3/MJD frequency is changing. Thus, we performed a systematic review and meta-analysis on phenomena with potential effect on SCA3/MJD recurrency in populations: instability of CAG repeat transmissions, anticipation, fitness, and segregation of alleles. Transmission of the mutant allele was associated with an increase of 1.23 CAG repeats in the next generation, and the average change in age at onset showed an anticipation of 7.75 years per generation; but biased recruitments cannot be ruled out. Affected SCA3/MJD individuals had 45% more children than related controls. Transmissions from SCA3/MJD carriers showed that the expanded allele was segregated in 64% of their children. In contrast, transmissions from normal subjects showed that the minor allele was segregated in 54%. The present meta-analysis concluded that there is a segregation distortion favoring the expanded allele, among children of carriers. Therefore, further studies on transmissions and anticipation phenomena as well as more observations about fertility are required to clarify these selective forces over SCA3/MJD.

Distribution of the CAG Triplet Repeat in ATXN1, ATXN3, and CACNA1A Loci in Peruvian Population.

Spinocerebellar ataxia subtypes 1, 3, and 6 (SCA1, MJD/SCA3, and SCA6) are among the most prevalent autosomal dominant cerebellar ataxias worldwide, but their relative frequencies in Peru are low. Frequency of large normal (LN) alleles at spinocerebellar ataxia-causative genes has been proposed to be associated with disease prevalence. To investigate the allelic distribution of the CAG repeat in ATXN1, ATXN3, and CACNA1A genes in a Peruvian mestizo population and examine their association with the relative frequency of SCA1, MJD/SCA3, and SCA6 across populations. We genotyped 213 healthy mestizo individuals from Northern Lima, Peru, for ATXN1, ATXN3, and CACNA1A using polymerase chain reaction (PCR) and polyacrylamide gel electrophoresis (PAGE). We compared the frequency of LN alleles and relative disease frequency between populations. We also tested 40 samples for CAT repeat interruptions within the CAG tract of ATXN1. We found no association between disease frequency and population frequency of LN alleles at ATXN1 and ATXN3. All 40 ATXN1 samples tested for CAT interruptions were positive. Frequency of LN alleles at CACNA1A correlates with SCA6 frequency across several populations, but this effect was largely driven by data from a single population. Low frequency of SCA1 and MJD/SCA3 in Peru is not explained by frequency of LN alleles at ATXN1 and ATXN3, respectively. The observed correlation between CACNA1A LN alleles and SCA6 frequency requires further assessment.

Founder Effects of Spinocerebellar Ataxias in the American Continents and the Caribbean.

Spinocerebellar ataxias (SCAs) comprise a heterogeneous group of autosomal dominant disorders. The relative frequency of the different SCA subtypes varies broadly among different geographical and ethnic groups as result of genetic drifts. This review aims to provide an update regarding SCA founders in the American continents and the Caribbean as well as to discuss characteristics of these populations. Clusters of SCAs were detected in Eastern regions of Cuba for SCA2, in South Brazil for SCA3/MJD, and in Southeast regions of Mexico for SCA7. Prevalence rates were obtained and reached 154 (municipality of Báguano, Cuba), 166 (General Câmara, Brazil), and 423 (Tlaltetela, Mexico) patients/100,000 for SCA2, SCA3/MJD, and SCA7, respectively. In contrast, the scattered families with spinocerebellar ataxia type 10 (SCA10) reported all over North and South Americas have been associated to a common Native American ancestry that may have risen in East Asia and migrated to Americas 10,000 to 20,000 years ago. The comprehensive review showed that for each of these SCAs corresponded at least the development of one study group with a large production of scientific evidence often generalizable to all carriers of these conditions. Clusters of SCA populations in the American continents and the Caribbean provide unusual opportunity to gain insights into clinical and genetic characteristics of these disorders. Furthermore, the presence of large populations of patients living close to study centers can favor the development of meaningful clinical trials, which will impact on therapies and on quality of life of SCA carriers worldwide.

Variation in DNA Repair System Gene as an Additional Modifier of Age at Onset in Spinocerebellar Ataxia Type 3/Machado-Joseph Disease.

Spinocerebellar ataxia type 3, or Machado-Joseph disease (SCA3/MJD), is caused by an expansion of CAG repeats, which is inversely correlated to age at onset (AO) of symptoms. However, on average, just 55.2% of variation in AO can be explained by expansion length. Additional modulators, such as polymorphic CAG tract in ATXN2 gene, can raise to 63.0% of the variation in AO. A sequence variation (rs3512) in FAN1 gene has previously been shown to be associated with late AO in Huntington's disease and polyglutaminopathies associated to ataxia. In the present study, genotype frequency of rs3512 was demonstrated in a cohort of SCA3/MJD patients from South Brazil, and these data were correlated to AO. The disease started 2.44 years earlier in subjects with the G/G genotype when compared to those subjects carrying the same CAGexp length at the ATXN3 gene and other genotypes (C/G and C/C) at rs3512. Placing together data on rs3512 genotype with data on CAG tract in ATXN2, AO of patients with G/G genotype was 2.58 years earlier, and a delay of 4.25 years was observed in patients that carry a short ATXN2 allele. Data presented here add further insights on the contribution of other factors in AO of SCA3/MJD beyond the causal mutation. Thus, well-known modifiers can help to unveil new ones and, as a whole, to better elucidate the mechanisms behind disease onset.

Childhood-Onset Spinocerebellar Ataxia 3: Tongue Dystonia as an Early Manifestation.

Background: Dystonia is a relatively common feature of spinocerebellar ataxia 3 (SCA3). Childhood onset of SCA3 is rare and typically associated with either relatively large, or homozygous, CAG repeat expansions. Case report: We describe a 10-year-old girl with SCA3, who presented with tongue dystonia in addition to limb dystonia and gait ataxia due to a heterozygous expansion of 84 repeats in ATXN3. Discussion: Diagnosis of the SCAs can be challenging, and even more so in children. Tongue dystonia has not previously been documented in SCA3.

Diagnosis of Spinocerebellar Ataxia in the West Indies.

Background: Access to medical care in many regions is limited by socioeconomic status, at both the individual and the community level. This report describes the diagnostic process of a family residing on an underserved Caribbean island where routine neurological care is typically addressed by general practitioners, and genetic diagnosis is not available through regular medical channels. The diagnosis and management of neurodegenerative disorders is especially challenging in this setting. Case Report: We diagnosed a family with spinocerebellar ataxia type 3 (SCA3) in an underdeveloped nation with limited access to genetic medicine and no full-time neurologist. Discussion: Molecular diagnosis of the SCAs can be challenging, even in developed countries. In the Caribbean, genetic testing is generally only available at a small number of academic centers. Diagnosis in this family was ultimately made by utilizing an international, pro bono, research-based collaborative process. Although access to appropriate resources, such as speech, physical, and occupational therapies, is limited on this island because of economic and geographical factors, the provision of a diagnosis appeared to be ultimately beneficial for this family. Identification of affected families highlights the need for access to genetic diagnosis in all communities, and can help direct resources where needed.

The Machado-Joseph disease-associated expanded form of ataxin-3: Overexpression, purification, and preliminary biophysical and structural characterization.

An expansion of the polyglutamine (polyQ) tract within the deubiquitinase ataxin-3 protein is believed to play a role in a neurodegenerative disorder. Ataxin-3 contains a Josephin catalytic domain and a polyQ tract that renders it intrinsically prone to aggregate, and thus full-length protein is difficult to characterize structurally by high-resolution methods. We established a robust protocol for expression and purification of wild-type and expanded ataxin-3, presenting 19Q and 74Q, respectively. Both proteins are monodisperse as assessed by analytical size exclusion chromatography. Initial biophysical characterization was performed, with apparent transition melting temperature of expanded ataxin-3 lower than the wild-type counterpart. We further characterize the molecular envelope of wild-type and expanded polyQ tract in ataxin-3 using small angle X-ray scattering (SAXS). Characterization of protein-protein interactions between ataxin-3 and newly identified binding partners will benefit from our protocol.

Planning Future Clinical Trials for Machado-Joseph Disease.

Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is an autosomal dominant multiple neurological systems degenerative disorder caused by a CAG repeat expansion at ATXN3 gene. Only a few treatments were evaluated in randomized clinical trials (RCT) in SCA3/MJD patients, with a lack of evidence for both disease-modifying and symptomatic therapies. The present chapter discuss in detail major methodological issues for planning future RCT for SCA3/MJD. There are several potential therapies for SCA3/MJD with encouraging preclinical results. Route of treatment, dosage titration and potential therapy biomarkers might differ among candidate drugs; however, the core study design and protocol will be mostly the same. RCT against placebo group is the best study design to test a disease-modifying therapy; the same cannot be stated for some symptomatic treatments. Main outcomes for future RCT are clinical scales: the Scale for the Assessment and Rating of ataxia (SARA) is currently the instrument of choice to prove efficacy of disease-modifying or symptomatic treatments against ataxia, the most important disease feature. Ataxia quantitative scales or its composite scores can be used as primary outcomes to provide preliminary evidence of efficacy in phase 2 RCT, due to a greater sensitivity to change. Details regarding eligibility criteria, randomization, sample size estimation, duration and type of analysis for both disease modifying and symptomatic treatment trials, were also discussed. Finally, a section anticipates the methodological issues for testing novel drugs when an effective treatment is already available. We conclude emphasizing four points, the first being the need of RCT for a number of different aims in the care of SCA3/MJD. Due to large sample sizes needed to warrant power, RCT for disease-modifying therapies should be multicenter enterprises. There is an urge need for surrogate markers validated for several drug classes. Finally, engagement of at risk or presymptomatic individuals in future trials will enable major advances on treatment research for SCA3/MJD.

Spinocerebellar ataxia type 3/Machado-Joseph disease: segregation patterns and factors influencing instability of expanded CAG transmissions.

Controversies about Mendelian segregation and CAG expansion (CAGexp) instabilities during meiosis in spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) need clarification. Additional evidence about these issues was obtained from the cohort of all SCA3/MJD individuals living in South Brazil. A survey was carried out to update information registered since 2001. Deaths were checked with the Public Information System, and data was made anonymous. Anticipation and delta-CAGexp from parent-offspring pairs, and delta-CAGexp between siblings were obtained. One hundred and fifty-nine families (94% of the entire registry) were retrieved, comprising 3725 living individuals as of 2015, 625 of these being symptomatic. Minimal prevalence was 6:100,000. Carriers of a CAGexp represented 65.6% of sibs in the genotyped offspring (p < 0.001). Median instability was larger among paternal than maternal transmissions, and instabilities correlated with anticipation (r = 0.38; p = 0.001). Age of the parent correlated to delta-CAGexp among 115 direct parent-offspring CAGexp transmissions (ρ = 0.23, p = 0.014). In 98 additional kindreds, the delta-CAGexp between 269 siblings correlated with their delta-of-age (ρ = 0.27, p < 0.0001). SCA3/MJD was associated with a segregation distortion favoring the expanded allele in our cohort. Instability of expansion during meiosis was weakly influenced by the age of the transmitting parent at the time of conception.

Dystonia in Machado-Joseph disease: Clinical profile, therapy and anatomical basis.

INTRODUCTION: Dystonia is frequent in Machado-Joseph disease, but several important aspects are not yet defined, such as the detailed clinical profile, response to treatment and anatomical substrate. METHODS: We screened 75 consecutive patients and identified those with dystonia. The Burke-Marsden-Fahn Dystonia Rating Scale was employed to quantify dystonia severity. Patients with dystonia received levodopa 600 mg/day for 2 months and were videotaped before and after treatment. A blinded evaluator rated dystonia in the videos. Patients with disabling dystonia who failed to respond to levodopa treatment received botulinum toxin. Finally, volumetric T1 and diffusion tensor imaging sequences were obtained in the dystonic group using a 3T-MRI scanner to identify areas of gray and white matter that were selectively damaged. RESULTS: There were 21 patients with dystonia (28%): 9 classified as generalized and 12 as focal/segmental. Patients with dystonia had earlier onset and larger (CAG) expansions (28.9 ± 11.7 vs 40.6 ± 11.4; p < 0.001 and 75 vs 70; p < 0.001, respectively). Although group analyses failed to show benefit on levodopa (p = 0.07), some patients had objective improvement. In addition, ten patients received botulinum toxin resulting in a significant change in dystonia scores after 4 weeks (p = 0.03). Patients with dystonia had atrophy at pre- and paracentral cortices; whereas, non-dystonic patients had occipital atrophy. Basal ganglia volume was reduced in both groups, but atrophy at the thalami, cerebellar white matter and ventral diencephali was disproportionately higher in the dystonic group. CONCLUSION: Dystonia in Machado-Joseph disease is frequent and often disabling, but may respond to levodopa. It is associated predominantly with structural abnormalities around the motor cortices and in the thalami.

Psychiatric disorders, spinocerebellar ataxia type 3 and CAG expansion.

Few studies have investigated the association between spinocerebellar ataxia type 3 (SCA3) and psychiatric disorders, using mainly screening scales to assess signs and symptoms of depression and anxiety. With these limitations in mind, we assessed the prevalence of DSM-IV Axis I psychiatric disorders in SCA3 patients and their possible associations with the length of CAG repeats and socio-demographic characteristics, highlighting potential risk factors. DNA samples were collected from 59 adults diagnosed with SCA3 for the quantification of CAG repeats. Next, the patients were assessed in respect to the presence of psychiatric disorders with the Structured Clinical Interview for DSM-IV. Approximately half of the sample had at least one psychiatric disorder (mood disorders 45.2 %), mainly dysthymia and current depression. There were no statistically significant differences in the length of CAG repeats between subjects with and without psychiatric disorders. The perception that SCA3 has a negative impact on life and the subjective assessment of current health status as poor emerged as risk factors for the occurrence of psychiatric disorders in the sample. There is a higher prevalence of psychiatric disorders in SCA3 patients compared to the general population. The lack of association between CAG repeats and occurrence of psychiatric disorders lends support to the hypothesis that psychiatric disorders in this group are associated with adaptive emotional responses to becoming ill.