Giunti, Paola

Abstract Alpha-tubulin 4A encoding gene (TUBA4A) has been associated with familial amyotrophic lateral sclerosis and frontotemporal dementia, based on identification of likely pathogenic variants in patients from distinct amyotrophic lateral sclerosis and frontotemporal dementia cohorts. By screening a multicentric French cohort of 448 unrelated probands presenting with cerebellar ataxia, we identified ultra-rare TUBA4A missense variants, all being absent from public databases and predicted pathogenic by multiple in silico tools. In addition, gene burden analyses in the 100 000 Genomes project (100KGP) showed enrichment of TUBA4A rare variants in the inherited ataxia group compared to controls [odds ratio: 57.0847 (10.2−576.7); P = 4.02 ×10−7]. Taken together, we report 12 patients presenting with spasticity and/or cerebellar ataxia and harbouring a predicted pathogenic TUBA4A missense mutation, including five confirmed de novo cases and a mutation previously reported in a large family presenting with spastic ataxia. Cultured fibroblasts from three patients harbouring distinct TUBA4A missense showed significant alterations in microtubule organization and dynamics, providing insight of TUBA4A variants pathogenicity. Our data confirm the identification of a hereditary spastic ataxia disease gene with variable age of onset, expanding the clinical spectrum of TUBA4A associated phenotypes.

AbstractBackground and purposeClinical trials in spinocerebellar ataxia type 3 (SCA3) will require biomarkers for use as outcome measures.MethodsTo evaluate total tau (t‐tau), glial fibrillary acidic protein (GFAP), ubiquitin carboxy‐terminal hydrolase L1 (UCHL1) and neurofilament light‐chain (NfL) as fluid biomarkers in SCA3, ATXN3 mutation carriers (n = 143) and controls (n = 172) were clinically assessed, and the plasma concentrations of the four proteins were analysed on the Simoa HD‐1 platform. Eleven ATXN3 mutation carrier cerebrospinal fluid samples were analysed for t‐tau and phosphorylated tau (p‐tau181). A transgenic SCA3 mouse model (MJDTg) was used to measure cerebellar t‐tau levels.ResultsPlasma t‐tau levels were higher in mutation carriers below the age of 50 compared to controls, and the Inventory of Non‐Ataxia Signs was associated with t‐tau in ataxic patients (p = 0.004). Pre‐ataxic carriers showed higher cerebrospinal fluid t‐tau and p‐tau181 concentrations compared to ataxic patients (p = 0.025 and p = 0.014, respectively). Cerebellar t‐tau was elevated in MJDTg mice compared to wild‐type (p = 0.033) only in the early stages of the disease. GFAP and UCHL1 did not show higher levels in mutation carriers compared to controls. Plasma NfL concentrations were higher in mutation carriers compared to controls, and differences were greater for younger carriers. The Scale for the Assessment and Rating of Ataxia was the strongest predictor of NfL in ataxic patients (p < 0.001).ConclusionOur results suggest that tau might be a marker of early disease stages in SCA3. NfL can discriminate mutation carriers from controls and is associated with different clinical variables. Longitudinal studies are required to confirm their potential role as biomarkers in clinical trials.

PolyQ ATXN3 is a pharmacodynamic marker for SCA3, and a SNP associated with the expanded allele may serve to specifically target mutant ATXN3 .