ATXN10 Microsatellite Distribution in a Peruvian Amerindian Population

Mechanistic and Therapeutic Insights into Ataxic Disorders with Pentanucleotide Expansions

Pentanucleotide expansion diseases constitute a special class of neurodegeneration. The repeat expansions occur in non-coding regions, have likely arisen from Alu elements, and often result in autosomal dominant or recessive phenotypes with underlying cerebellar neuropathology. When transcribed (potentially bidirectionally), the expanded RNA forms complex secondary and tertiary structures that can give rise to RNA-mediated toxicity, including protein sequestration, pentapeptide synthesis, and mRNA dysregulation. Since several of these diseases have recently been discovered, our understanding of their pathological mechanisms is limited, and their therapeutic interventions underexplored. This review aims to highlight new in vitro and in vivo insights into these incurable diseases.

Genetic epidemiology of familial ALS in Brazil

Many genes associated with familial forms of the amyotrophic lateral sclerosis (fALS) have been identified in European and North American cohorts. However, little is known about the genetic bases of fALS in Latin America and Brazil, in particular. To address this question, we recruited 107 patients with fALS from 93 unrelated families from Southeastern, Southern, and Northeastern regions of the country. A 3-step diagnostic approach was used: 1) Triplet repeat primed polymerase chain reaction to search for C9orf72 expansions, then 2) fragment digestion to search for the c.166 C>T VAPB variant, and finally, 3) whole exome sequencing for those who tested negative. We identified the genetic cause for fALS in 70% of the families. VAPB and C9orf72 were the most frequent genes (30% and 22%, respectively), followed by SOD1, TARDBP, ANXA11, and FUS. Five novel variants in known ALS genes were found, including the SOD1 Val120Leu and ANXA11 Asp40Tyr, which were seen in 2 unrelated families each. In conclusion, VAPB and then C9orf72 are the genes most commonly related to fALS in Brazil.

Diagnostic Yield of Whole Exome Sequencing for Adults with Ataxia: a Brazilian Perspective

Previous studies using whole exome sequencing (WES) have shown that a significant proportion of adult patients with undiagnosed ataxia in European and North American cohorts have a known genetic cause. Little is known about the diagnostic yield of WES in non-Caucasian ataxic populations. Herein, we used WES to investigate a Brazilian cohort of 76 adult patients with idiopathic ataxia previously screened for trinucleotide expansions in known ataxia genes. We collected clinical and radiological data from each patient. WES was performed following standard procedures. Only variants labeled as pathogenic or likely pathogenic according to American college of medical genetics and genomics (ACMG) criteria were retrieved. We determined the diagnostic yield of WES for the whole cohort and also for subgroups defined according to presence or not of pyramidal signs, peripheral neuropathy, and cerebellar atrophy. There were 41 women and 35 men. Mean age at testing was 48 years. Pyramidal signs, peripheral neuropathy, tremor, and cerebellar atrophy were found in 38.1%, 13.1%, 10.5%, and 68.3% of all subjects, respectively. Diagnostic yield of WES was 35.5%. Thirty-six distinct mutations were found in 20 different genes, determining the diagnosis of 18 autosomal recessive and 9 autosomal dominant ataxias. SACS and SPG7 were the most frequently found underlying genes. WES performed better in the subgroup with vs the subgroup without spasticity (p = 0.005). WES was diagnostic in 35.5% of cases of the Brazilian cohort of ataxia cases. These results have implications for diagnosis, genetic counseling and eventually treatment.