Erdmann Hannes, Schaub Annalisa, Lucas Morghan C, Scholz Veronika, Benet-Pages Anna, Becker Kerstin, Dineiger Christine, Mayer Veronika, van Buren Inga, Breithausen Eva, Akbari Karl, Cordts Isabell, Sauer Mayra, Schneider Christine, Krakowsky Rosanna, Schnabel Franziska, Dunker Konstanze, Fabritius Lena, Gerb Johannes, Grabova Denis, Möhwald Ken, Näher Marius, Steinmetz Karoline, Thiessen Franziska, Jäck Alexander, Schneider-Gold Christiane, Zittel Simone, Petersen Christina, Schreyer Isolde, Mämecke Larissa, Wilfling Sibylle, Wunderlich Gilbert, Brenner David, Hellenbroich Yorck, Muhle Kirsten, Huchtemann Tessa, Claus Inga, Klopstock Thomas, Strupp Michael, Levin Johannes, Höglinger Günter, Huppert Doreen, Becker-Bense Sandra, Filippopulos Filipp, Kilpert Fabian, Leitão Elsa, Kaya Sabine, Depienne Christel, Schöberl Florian, Neuhann Teresa, Holinski-Feder Elke, Zwergal Andreas, Abicht Angela
Medical Genetics Center (MGZ) Munich, 80335 Munich, Germany.
Friedrich Baur Institute at the Department of Neurology, LMU University Hospital, Ludwig-Maximilians-Universität München, 80336 Munich, Germany.
Brain. 2025 Sep 3. doi: 10.1093/brain/awaf318.
Hereditary adult-onset ataxias are a heterogeneous group of phenotypically overlapping conditions, often caused by pathogenic expansions of short tandem repeats. Currently, 18 repeat disorders with a core phenotype of adult-onset ataxia are known. Diagnosis typically relies on sequential PCR-based methods, which are labour-intensive and lack precision. Long-read sequencing (LRS) has the potential to overcome these limitations and is currently implemented and validated in clinical genetics. Using clinical nanopore Cas9-targeted sequencing (Clin-CATS) for parallel in-depth repeat analysis, we evaluated a diagnostic cohort of 513 adult-onset ataxia patients, determining frequencies of all known repeat-associated ataxias except Spinocerebellar ataxia 4 (SCA4), as well as the carrier frequencies for autosomal-recessive disorders, RFC1 spectrum disorder and Friedreich's ataxia (FRDA). Additionally, phenotypes of patients with established genetic diagnoses were characterized, especially those of patients living with RFC1 spectrum disorder and SCA27B. Repeat-associated ataxias were confirmed in 33.3% of cases, including rare ataxias, such as SCA10, SCA36 and SCA37, alongside as the most prevalent conditions SCA27B and RFC1 spectrum disorder. Potentially pathogenic expansions in FGF14 were identified in an additional 4.7% of patients. Testing of another 347 patients for ZFHX3 expansions linked to SCA4 did not identify any cases. Dual diagnoses were frequent, occuring in 6.4% of patients with repeat-associated ataxia. We confirmed a high RFC1 spectrum disorder carrier frequency (7.2%) and reclassified certain FXN expansions as likely non-pathogenic, resulting in a lower than estimated carrier frequency for FRDA of 0.8%. We also identified novel repeat configurations in several loci and illustrated the high heterogeneity of repeat expansions in RFC1, highlighting it as a potential source of false results when using PCR-based methods. This study underscores the diagnostic advantages of LRS for comprehensive repeat analysis and recommends its adoption as a standard in clinical genetics, replacing Southern blot and PCR-based approaches. Furthermore, based on our findings in a large patient cohort a re-evaluation of existing phenotype-genotype correlations is recommended as well as evaluating additional parameters besides repeat length to improve diagnostic precision of repeat analysis.
遗传性成人起病共济失调是一组表型重叠的异质性疾病，通常由短串联重复序列的致病性扩增引起。目前，已知有18种以成人起病共济失调为核心表型的重复序列疾病。诊断通常依赖于基于PCR的序贯方法，这些方法 labor-intensive且缺乏精确性。长读长测序（LRS）有潜力克服这些局限性，目前已在临床遗传学中实施并得到验证。我们使用临床纳米孔Cas9靶向测序（Clin-CATS）进行平行深入的重复序列分析，评估了513例成人起病共济失调患者的诊断队列，确定了除脊髓小脑共济失调4型（SCA4）外所有已知的重复序列相关共济失调的频率，以及常染色体隐性疾病、RFC1谱系障碍和弗里德赖希共济失调（FRDA）的携带者频率。此外，对已确诊遗传疾病患者的表型进行了特征描述，特别是那些患有RFC1谱系障碍和SCA27B的患者。在33.3%的病例中确诊了重复序列相关共济失调，包括罕见的共济失调，如SCA10、SCA36和SCA37，以及最常见的疾病SCA27B和RFC1谱系障碍。在另外4.7%的患者中发现了FGF14中的潜在致病性扩增。对另外347例患者进行与SCA4相关的ZFHX3扩增检测，未发现任何病例。双重诊断很常见，在6.4%的重复序列相关共济失调患者中出现。我们确认了较高的RFC1谱系障碍携带者频率（7.2%），并将某些FXN扩增重新分类为可能无致病性，导致FRDA的携带者频率低于估计值，为0.8%。我们还在几个基因座中发现了新的重复序列构型，并说明了RFC1中重复序列扩增的高度异质性，突出了它在使用基于PCR的方法时作为错误结果潜在来源的问题。这项研究强调了LRS在全面重复序列分析中的诊断优势，并建议将其作为临床遗传学的标准方法采用，取代Southern印迹法和基于PCR的方法。此外，基于我们在大量患者队列中的发现，建议重新评估现有的表型-基因型相关性，并评估除重复序列长度之外的其他参数，以提高重复序列分析的诊断准确性。
