Extreme phenotypic heterogeneity in non-expansion spinocerebellar ataxias

Paulina Cunha, Emilien Petit, Marie Coutelier, Giulia Coarelli, Caterina Mariotti, Jennifer Faber, Judith Van Gaalen, Joana Damasio, Zofia Fleszar, Michele Tosi, Clarissa Rocca, Giovanna De Michele, Martina Minnerop, Claire Ewenczyk, Filippo M. Santorelli, Anna Heinzmann, Thomas Bird, Matthias Amprosi, Elisabetta Indelicato, Alberto BenussiPerrine Charles, Claudia Stendel, Silvia Romano, Marina Scarlato, Isabelle Le Ber, Maria Teresa Bassi, Mercedes Serrano, Tanja Schmitz-Hübsch, Sarah Doss, Gijs A.J. Van Velzen, Quentin Thomas, Antonio Trabacca, Juan Dario Ortigoza-Escobar, Stefano D'Arrigo, Dagmar Timmann, Chiara Pantaleoni, Andrea Martinuzzi, Elsa Besse-Pinot, Luca Marsili, Ettore Cioffi, Francesco Nicita, Alejandro Giorgetti, Isabella Moroni, Romina Romaniello, Carlo Casali, Penina Ponger, Giorgio Casari, Susanne T. De Bot, Giovanni Ristori, Lubov Blumkin, Barbara Borroni, Cyril Goizet, Cecilia Marelli, Sylvia Boesch, Mathieu Anheim, Alessandro Filla, Henry Houlden, Enrico Bertini, Thomas Klopstock, Matthis Synofzik, Florence Riant, Ginevra Zanni, Stefania Magri, Daniela Di Bella, Lorenzo Nanetti, Jorge Sequeiros, Jorge Oliveira, Bart Van de Warrenburg, Ludger Schöls, Franco Taroni, Alexis Brice, Alexandra Durr*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Although the best-known spinocerebellar ataxias (SCAs) are triplet repeat diseases, many SCAs are not caused by repeat expansions. The rarity of individual non-expansion SCAs, however, has made it difficult to discern genotype-phenotype correlations. We therefore screened individuals who had been found to bear variants in a non-expansion SCA-associated gene through genetic testing, and after we eliminated genetic groups that had fewer than 30 subjects, there were 756 subjects bearing single-nucleotide variants or deletions in one of seven genes: CACNA1A (239 subjects), PRKCG (175), AFG3L2 (101), ITPR1 (91), STUB1 (77), SPTBN2 (39), or KCNC3 (34). We compared age at onset, disease features, and progression by gene and variant. There were no features that reliably distinguished one of these SCAs from another, and several genes—CACNA1A, ITPR1, SPTBN2, and KCNC3—were associated with both adult-onset and infantile-onset forms of disease, which also differed in presentation. Nevertheless, progression was overall very slow, and STUB1-associated disease was the fastest. Several variants in CACNA1A showed particularly wide ranges in age at onset: one variant produced anything from infantile developmental delay to ataxia onset at 64 years of age within the same family. For CACNA1A, ITPR1, and SPTBN2, the type of variant and charge change on the protein greatly affected the phenotype, defying pathogenicity prediction algorithms. Even with next-generation sequencing, accurate diagnosis requires dialogue between the clinician and the geneticist.

Original languageEnglish
Pages (from-to)1098-1109
Number of pages12
JournalAmerican Journal of Human Genetics
Issue number7
StatePublished - 6 Jul 2023


  • Spinocerebellar Ataxia, SCA, CACNA1A, PRKCG, AFG3L2, ITPR1, STUB1, SPTBN2, KCNC3, onset


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