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Background: RFC1‐related disorder (RFC1/CANVAS) shares clinical features with other late‐onset ataxias, such as spinocerebellar ataxias (SCA) and multiple system atrophy cerebellar type (MSA‐C). Thinning of cranial nerves V (CNV) and VIII (CNVIII) has been reported in magnetic resonance imaging (MRI) scans of RFC1/CANVAS, but its specificity remains unclear. Objectives: To assess the usefulness of CNV and CNVIII thinning to differentiate RFC1/CANVAS from SCA and MSA‐C. Methods: Seventeen individuals with RFC1/CANVAS, 57 with SCA (types 2, 3 and 6), 11 with MSA‐C and 15 healthy controls were enrolled. The Balanced Fast Field Echo sequence was used for assessment of cranial nerves. Images were reviewed by a neuroradiologist, who classified these nerves as atrophic or normal, and subsequently the CNV was segmented manually by an experienced neurologist. Both assessments were blinded to patient and clinical data. Non‐parametric tests were used to assess between‐group comparisons. Results: Atrophy of CNV and CNVIII, both alone and in combination, was significantly more frequent in the RFC1/CANVAS group than in healthy controls and all other ataxia groups. Atrophy of CNV had the highest sensitivity (82%) and combined CNV and CNVIII atrophy had the best specificity (92%) for diagnosing RFC1/CANVAS. In the quantitative analyses, CNV was significantly thinner in the RFC1/CANVAS group relative to all other groups. The cutoff CNV diameter that best identified RFC1/CANVAS was ≤2.2 mm (AUC = 0.91; sensitivity 88.2%, specificity 95.6%). Conclusion: MRI evaluation of CNV and CNVIII using a dedicated sequence is an easy‐to‐use tool that helps to distinguish RFC1/CANVAS from SCA and MSA‐C. [ABSTRACT FROM AUTHOR]

Background: Ataxia telangiectasia is one of the most common causes of autosomal recessive cerebellar ataxias. However, absence of telangiectasia, normal levels of alpha‐fetoprotein and negative genetic test may direct to alternative diagnosis with similar phenotypes such as ataxia telangiectasia‐like disorders (ATLD). Cases: We report two instructive cases of ATLD: the first case with ataxia telangiectasia‐like disorder type 1 related to MRE11A gene, and the second case with ataxia telangiectasia‐like disorder type 2 related to PCNA gene. Literature Review: ATLD is an unusual group of autosomal recessive diseases that share some clinical features and pathophysiological mechanisms with ataxia telangiectasia (AT). ATLD may be associated with mutations in the MRE11A (ATLD type 1) and PCNA (ATLD type 2) genes. ATLD belongs to the group of chromosomal instability syndromes. The reason for the term ATLD is related to the similar pathophysiological mechanisms observed in AT, which is characterized by chromosomal instability and radiosensitivity. Conclusions: In this review, the main clinical features, biomarkers, brain imaging and genetics of ATLD are discussed. Mutations in the MRE11A and PCNA genes should be included in the differential diagnosis for early onset cerebellar ataxia with absence of telangiectasia and normal levels of alpha‐fetoprotein. View Supplementary Video 1 [ABSTRACT FROM AUTHOR]

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