Sławek, Jarosław

Abstract Background Spinocerebellar ataxia type 3 (SCA3), the most common autosomal dominant ataxia, is driven by the accumulation of polyglutamine‐expanded (polyQ) ATXN3 proteins. While promising as biomarkers, their longitudinal trajectories across multiple biofluids remain poorly defined. Objectives To quantify polyQ ATXN3 levels in cerebrospinal fluid (CSF), plasma, and urine within a comprehensive cohort, utilizing serial measurements to map protein dynamics. Methods We employed a validated immunoassay to quantify polyQ ATXN3 in 97 symptomatic and 13 presymptomatic SCA3 patients, correlating levels with clinical features, ancestry, disease status, and longitudinal progression. Results Asian participants exhibited lower plasma but elevated urinary polyQ ATXN3 levels relative to other ancestries. While CSF levels were higher in symptomatic patients at baseline, they showed a significant longitudinal decline. Conclusions PolyQ ATXN3 is a viable multi‐biofluid biomarker. Declining CSF levels likely reflect neurodegeneration, supporting its role in tracking progression and emphasizing the need for ancestry‐based adjustment in trials. © 2026 International Parkinson and Movement Disorder Society.

Abstract Leigh syndrome (LS) is a progressive neurodegenerative disease, characterized by extensive clinical, biochemical, and genetic heterogeneity. Recently, biallelic variants in DNAJC30 gene, encoding a protein crucial for the repair of mitochondrial complex I subunits, have been associated with Leber hereditary optic neuropathy and LS. It was suggested that clinical heterogeneity of DNAJC30 ‐associated mitochondrial disease may be attributed to digenic inheritance. We describe three Polish patients, a 9‐year‐old boy, and female and male siblings, aged 17 and 11 years, with clinical and biochemical manifestations of LS. Exome sequencing (ES) identified a homozygous pathogenic variant in DNAJC30 c.152A>G, p.(Tyr51Cys) in the 9‐year‐old boy. In the siblings, ES identified two DNAJC30 variants: c.152A>G, p.(Tyr51Cys) and c.130_131del, p.(Ser44ValfsTer8) in a compound heterozygous state. In addition, both siblings carried a novel heterozygous c.484G>T, p.(Val162Leu) variant in NDUFS8 gene. This report provides further evidence for the association of DNAJC30 variants with LS. DNAJC30 ‐associated LS is characterized by variable age at onset, movement disorder phenotype and normal or moderately elevated blood lactate level. Identification of a candidate heterozygous variant in NDUFS8 supports the hypothesis of digenic inheritance. Importantly, DNAJC30 pathogenic variants should be suspected in patients with LS irrespective of optic nerve involvement.