A rare subtype of type I autosomal dominant cerebellar ataxia (ADCA type I). It is characterized by a variable clinical picture which can include dementia, psychiatric disorders, parkinsonism, dystonia, chorea, spasticity, and epilepsy¹.

Prevalence

0.2 100,000

Unknown (global), <100 families, 0.47:1,000,000 (Japanese), 0.16/100,000 (England)^2,3: 0.2/100,000. Found across ethnicities/ancestries, with population-dependent prevalence².

Age of Onset

Typical: 19-48; Range: 3-75⁴, has a second variant to delay onset⁵.

HPO Terms

HP:0000020 Urinary incontinence HP:0000473 Torticollis HP:0000640 Gaze-evoked nystagmus HP:0000643 Blepharospasm HP:0000708 Atypical behavior HP:0000716 Depression HP:0000718 Aggressive behavior HP:0000726 Dementia HP:0000727 Frontal lobe dementia HP:0000738 Hallucinations HP:0000743 Frontal release signs HP:0000757 Lack of insight HP:0001250 Seizure HP:0001251 Ataxia HP:0001257 Spasticity HP:0001260 Dysarthria HP:0001268 Mental deterioration HP:0001272 Cerebellar atrophy HP:0001288 Gait disturbance HP:0001289 Confusion HP:0001300 Parkinsonism HP:0001310 Dysmetria HP:0001332 Dystonia HP:0001336 Myoclonus HP:0002015 Dysphagia HP:0002063 Rigidity HP:0002066 Gait ataxia HP:0002067 Bradykinesia HP:0002070 Limb ataxia HP:0002072 Chorea HP:0002080 Intention tremor HP:0002136 Broad-based gait HP:0002171 Gliosis HP:0002186 Apraxia HP:0002300 Mutism HP:0002356 Writer's cramp HP:0002403 Positive Romberg sign HP:0002506 Diffuse cerebral atrophy HP:0002529 Neuronal loss in central nervous system HP:0004305 Involuntary movements HP:0007058 Generalized cerebral atrophy/hypoplasia HP:0007256 Abnormal pyramidal sign HP:0007366 Atrophy/Degeneration affecting the brainstem HP:0007668 Impaired pursuit initiation and maintenance HP:0011999 Paranoia HP:0012082 Cerebellar Purkinje layer atrophy

Association

Mendelian

Locus

hg19 chr6:170870994-170871105

hg38 chr6:170561906-170562017

t2t chr6:171935458-171935569

Details

Benign range is 25-40 repeats, pathogenic range is 49+ repeats (largest to date 66 motifs, with mild correlation between size and age of onset), and intermediate alleles (41-48 repeats) are associated with reduced penetrance and potentially milder phenotypes². Huntington's disease-like phenotype⁶. CAA CAG CAA interruption is seen in all alleles stably transmitted across generations^2,7.

Mechanism

LoF/GoF

Polyglutamine expansion leading to transcriptional dysregulation⁸.

Detection

Short-read sequencing is reported to detect expansions but cannot size alleles beyond 250 bp. PCR amplification may detect expansions of ≤66 repeats^9,2.

Year

1999¹⁰

Location in Gene

Coding Exon 3

Gene Strand

Alleles

Ref. Motif

CAG

Ranges

Benign (ref.)

–

Benign (gene)

–

Pathogenic (ref.)

CAG

Pathogen. (gene)

CAG

Unknown (ref.)

–

Unknown (gene)

–

Interruption (ref.)

CAA

Interrup. (gene)

CAA

gnomAD

Pathogenic genotype frequency data is not displayed for this locus because a substantial number of large alleles failed manual review by the gnomAD team.

References

Direct supporting references for info on this page.

Ontology Lookup Service (OLS)

mondo:0011781

Spinocerebellar Ataxia Type 17

Yasuko,Toyoshima, Osamu,Onodera, Mitsunori,Yamada, Shoji,Tsuji, Hitoshi,Takahashi

GeneReviews® · 1993-01-01

genereviews:NBK1438

Profiling of Short-Tandem-Repeat Disease Alleles in 12,632 Human Whole Genomes.

Haibao,Tang, Ewen F,Kirkness, Christoph,Lippert, William H,Biggs, Martin,Fabani, Ernesto,Guzman, Smriti,Ramakrishnan, Victor,Lavrenko, Boyko,Kakaradov, Claire,Hou, Barry,Hicks, David,Heckerman, Franz J,Och, C Thomas,Caskey, J Craig,Venter, Amalio,Telenti

American journal of human genetics · 2017-11-02

pmid:29100084

4pmid:18418687

5omim:607136

Huntington's disease-like phenotype due to trinucleotide repeat expansions in the TBP and JPH3 genes.

Giovanni,Stevanin, Hiroto,Fujigasaki, Anne-Sophie,Lebre, Agnes,Camuzat, Cecile,Jeannequin, Catherine,Dode, Junko,Takahashi, Chankranira,San, Robert,Bellance, Alexis,Brice, Alexandra,Durr

Brain : a journal of neurology · 2003-05-06

pmid:12805114

Comprehensive genetic diagnosis of tandem repeat expansion disorders with programmable targeted nanopore sequencing.

Igor,Stevanovski, Sanjog R,Chintalaphani, Hasindu,Gamaarachchi, James M,Ferguson, Sandy S,Pineda, Carolin K,Scriba, Michel,Tchan, Victor,Fung, Karl,Ng, Andrea,Cortese, Henry,Houlden, Carol,Dobson-Stone, Lauren,Fitzpatrick, Glenda,Halliday, Gianina,Ravenscroft, Mark R,Davis, Nigel G,Laing, Avi,Fellner, Marina,Kennerson, Kishore R,Kumar, Ira W,Deveson

Science advances · 2022-03-04

pmid:35245110

Molecular Mechanisms in Pentanucleotide Repeat Diseases.

Joana R,Loureiro, Ana F,Castro, Ana S,Figueiredo, Isabel,Silveira

Cells · 2022-01-08

pmid:35053321

The Frequency of Intermediate Alleles in Patients with Cerebellar Phenotypes.

Elena,Capacci, Silvia,Bagnoli, Giulia,Giacomucci, Costanza Maria,Rapillo, Alessandra,Govoni, Valentina,Bessi, Cristina,Polito, Irene,Giotti, Alice,Brogi, Elisabetta,Pelo, Sandro,Sorbi, Benedetta,Nacmias, Camilla,Ferrari

Cerebellum (London, England) · 2023-10-31

pmid:37906407

A neurological disease caused by an expanded CAG trinucleotide repeat in the TATA-binding protein gene: a new polyglutamine disease?

R,Koide, S,Kobayashi, T,Shimohata, T,Ikeuchi, M,Maruyama, M,Saito, M,Yamada, H,Takahashi, S,Tsuji

Human molecular genetics · 1999-10-01

pmid:10484774

Additional Literature

Additional literature related to this locus.

Raw PubMed search results
(All PubMed results returned by searching for this gene, tandem repeats, and disease, in medline format)

Diagnostic redirection in dementia-first spinocerebellar ataxia type 17: a family-based case report and focused literature review.

Siqi,Zhang, Xie,Zhang, Lijuan,Li, Bingling,Zhou, Wei,Shao

Frontiers in neuroscience · 2026-07-13

pmid:42516548

Computational Short Tandem Repeat Genotyping Reveals Clinically Relevant Expansions in a Large Turkish Neurodegeneration Disease Cohort.

Zakhiriddin,Khojakulov, Robin J,Palvadeau, Müge,Kovancılar-Koç, Irmak,Atay, Irmak,Şahbaz, Şeyma,Tekgül, Ayça,Şahin, Esmer Zeynep Duru,Badakal, Tuğçe,Gül-Demirkale, Vildan,Çiftçi, Elif,Bayraktar, Ceren,Tunca, Natalia,Smolina, Fulya,Akçimen, Ayşe Nazlı,Başak

International journal of molecular sciences · 2026-05-13

pmid:42196324

Detection of short tandem repeat expansions on a targeted neurological gene panel using STRipy improves the diagnostic rate for ataxias.

Carolin K,Scriba, Chiara,Folland, Michael,Black, Jessica,Baker, Daniel,Abromeit, Samantha,Saw, Mei-Ting,Chiew, Rebecca,Gooding, Nigel G,Laing, Mark R,Davis, Gianina,Ravenscroft

Brain communications · 2026-03-16

pmid:42038259

Childhood-Onset Huntington's Disease-Like Presentation of SCA17 with Intermediate Repeats, A Case Report.

Meaghan,Berns, Kelsey,Jensen, Laura,Speltz, Leonardo Brito,Almeida

Cerebellum (London, England) · 2026-03-17

pmid:41843312

Short tandem repeat expansions in patients with neurodegenerative dementia.

Yuan,Zhu, Xuewen,Xiao, Yiliang,Liu, Zheng,Wang, Tengfei,Luo, Tianyan,Xu, Qijie,Yang, Xiaoli,Hao, Cong,Zhang, Sizhe,Zhang, Shilin,Luo, Yafang,Zhou, Xinxin,Liao, Yun,Tian, Ling,Weng, Liangjuan,Fang, Beisha,Tang, Bin,Jiao, Jinchen,Li, Lu,Shen

EBioMedicine · 2026-02-26

pmid:41762523

Repeat Variants, Biomarkers, and Molecular Signatures in Parkinson's Disease:

Jose Miguel,Laffita-Mesa, Martin,Paucar, Per,Svenningsson

International journal of molecular sciences · 2025-09-20

pmid:41009775

Diagnostic yield and limitations of whole-genome sequencing for hereditary cerebellar ataxia.

Wai Yan,Yau, Roisin,Sullivan, Emer,O'Connor, David,Pellerin, Michael H,Parkinson, Paola,Giunti, Marie-Josée,Dicaire, Matt C,Danzi, Stephan,Züchner, Bernard,Brais, Nicholas W,Wood, Henry,Houlden, Jana,Vandrovcova

Brain communications · 2025-05-17

pmid:40488180

Isolated Generalized Chorea in a Patient with Small-Expanded Allele Spinocerebellar Ataxia 17.

Giulia,Paparella, Martina,De Riggi, Simone,Aloisio, Adriana,Martini, Luca,Angelini, Daniele,Birreci, Davide,Costa, Antonio,Cannavacciuolo, Anna Maria,Griguoli, Stefano,Gambardella, Matteo,Bologna

Cerebellum (London, England) · 2025-06-06

pmid:40478462

TBP Repeat Expansion Analysis in Patients Carrying Heterozygous STUB1 Variants.

Jonathan,De Winter, Liedewei,Van de Vondel, Kristof,Van Schil, Tine,Deconinck, Katrien,Storm, Karine,Geens, Charlotte,Sommeling, David,Crosiers, Emke,Marechal, Willem,De Ridder, Peter,De Jonghe, Jonathan,Baets

Movement disorders : official journal of the Movement Disorder Society · 2025-02-14

pmid:39950762

Locus SCA17 TBP

Disease

Locus

Alleles

gnomAD

References

Additional Literature