Cortico-basal Syndrome (CBS) is a heterogeneous neurodegenerative disorder with significant genetic contributors. Unlike Alzheimer's disease or Parkinson's disease, CBS shows relatively low heritability, but genetic factors play an important role in disease risk, age of onset, and phenotypic expression[1]. Approximately 10-20% of CBS cases have an identifiable genetic cause, with mutations in several genes associated with frontotemporal dementia and 4R tauopathies.
The MAPT (Microtubule-Associated Protein Tau) gene encodes the tau protein, which is central to tau pathology in CBS. MAPT mutations were among the first genetic causes identified in CBS:
| Mutation | Effect | CBS Phenotype |
|---|---|---|
| P301S | Tau filament formation | Classic CBS with early cognitive decline |
| G389R | Altered splicing | CBS-PDP phenotype |
| R406W | Tau hyperphosphorylation | CBS with prominent aphasia |
| IVS10+16 | Exon 10 splicing disruption | CBS/PSP overlap |
Key Points:
GRN mutations cause progranulin deficiency and are one of the most common genetic causes of CBS:
Clinical Features in GRN carriers:
The C9orf72 hexanucleotide repeat expansion is a major genetic cause of CBS, particularly in cases with FTD/ALS overlap:
Phenotype in C9orf72 carriers:
Large-scale genome-wide association studies have identified several risk loci for CBS and related 4R tauopathies[6]:
| Locus | Gene | Odds Ratio | Function |
|---|---|---|---|
| 17q21.31 | MAPT (H1 haplotype) | 1.8-3.1 | Tau protein |
| 1p32.3 | STX6 | 1.2-1.4 | Vesicle trafficking |
| 19q13.32 | TMEM106B | 1.3-1.5 | Lysosomal function |
| 3p22.1 | MOBP | 1.2-1.3 | Myelin integrity |
| 11p11.2 | DLGAP5 | 1.1-1.2 | Cell division |
Emerging evidence suggests polygenic risk scores combining multiple variants may help predict:
However, polygenic risk scores for CBS remain less validated than for Alzheimer's disease or Parkinson's disease.
| Gene | Motor Onset | Cognitive Features | Neuropsychiatric | Progression |
|---|---|---|---|---|
| MAPT | Moderate | Early dementia | Depression | Moderate |
| GRN | Asymmetric | Aphasia prominent | Disinhibition | Moderate |
| C9orf72 | Often symmetric | Early dysexecutive | Depression, psychosis | Rapid |
| Sporadic | Asymmetric | Late cognitive | Anxiety, apathy | Variable |
Genotype influences the underlying pathology in CBS[7]:
Genetic testing should be considered in CBS patients with:
Recommended testing panel:
Understanding the genetic basis of CBS has therapeutic implications:
| Clinical Feature | Consideration |
|---|---|
| Age <55 at onset | Strongly consider |
| Family history (FTD/ALS) | Essential |
| Prominent aphasia | Consider GRN testing |
| Rapid progression + psychosis | Consider C9orf72 testing |
| PSP-like features | Consider MAPT testing |
Pathogenic variants:
Variants of uncertain significance (VUS):
Negative testing:
Dickson et al. Neuropathology of corticobasal degeneration. Acta Neuropathol Commun. 2020. ↩︎
Rohrer et al. Clinical heterogeneity of corticobasal syndrome associated with GRN mutations. Neurology. 2011. ↩︎
Mott et al. C9orf72 repeat expansions in corticobasal syndrome. Neurology. 2019. ↩︎
Stamelou et al. Tmem106b genetic variants in corticobasal degeneration. Mov Disord. 2019. ↩︎
Kouri et al. Genome-wide association study of corticobasal degeneration. Ann Neurol. 2015. ↩︎
Chen et al. Identification of novel risk loci for corticobasal degeneration. Brain. 2018. ↩︎
Arrone et al. Genetic overlap between corticobasal degeneration and frontotemporal dementia. JAMA Neurol. 2019. ↩︎