Progressive Supranuclear Palsy (PSP) is a tauopathy characterized by progressive postural instability, vertical supranuclear gaze palsy, and cognitive impairment. Genetic studies have identified strong associations between PSP and variants in the MAPT (microtubule-associated protein tau) gene, particularly the H1 haplotype, which accounts for a significant portion of genetic risk. Specific pathogenic mutations in MAPT also cause familial PSP.
PSP is a 4-repeat tauopathy with the following genetic architecture:
- MAPT H1 haplotype: Major risk factor, ~40% of genetic susceptibility
- Specific MAPT mutations: Cause familial PSP (P301L, ΔN296, etc.)
- Other risk genes: STX6, MOBP, EIF2AK3
The MAPT gene has two major haplotypes, H1 and H2. The H1 haplotype is overrepresented in PSP patients:
- Mechanism: The H1 haplotype has increased expression of 3R and 4R tau isoforms
- Risk: H1/H1 genotype increases PSP risk by 3-5 fold compared to H1/H2
- Prevalence: >95% of PSP patients are H1/H1
The H1 haplotype contains several single nucleotide polymorphisms (SNPs) that tag the risk allele:
- rs1800547
- rs242557
- rs2471738
The P301L mutation in MAPT is one of the most common pathogenic mutations causing familial PSP:
- Inheritance: Autosomal dominant
- Penetrance: High (~90% by age 60)
- Phenotype: Classic PSP phenotype with early onset
- Mechanism: Mutation promotes tau aggregation and reduces microtubule binding
This mutation affects tau exon 10 splicing:
- Effect: Increases 4R tau isoform production
- Phenotype: PSP phenotype with prominent supranuclear gaze palsy
- Family history: Often autosomal dominant
- P301S: Rare mutation with PSP phenotype
- K369I: Reported in families with PSP features
- R5L: Associated with PSP in some families
Genome-wide association studies (GWAS) have identified STX6 as a risk gene for PSP:
- Function: Involved in vesicle trafficking
- Mechanism: May affect tau secretion or propagation
- Effect size: Modest odds ratio (~1.2)
MOBP variants are associated with PSP risk:
- Function: Myelin maintenance in the brain
- Mechanism: May affect white matter integrity
Variants in EIF2AK3, encoding the PERK protein involved in the unfolded protein response:
- Function: ER stress response
- Mechanism: May affect tau processing
The genetic variants in MAPT lead to tau dysfunction:
- Hyperphosphorylation: Increased tau kinase activity leads to abnormal tau phosphorylation
- Aggregation: Phosphorylated tau forms neurofibrillary tangles
- Microtubule dysfunction: Tau normally stabilizes microtubules; loss of function disrupts axonal transport
- Tau spreading: Pathological tau may spread between neurons via synaptic connections
The H1 haplotype likely increases risk through:
- Increased expression of 4R tau (exon 10 inclusion)
- Altered splicing efficiency
- Promoter activity differences
Genetic testing for PSP is considered in:
- Early-onset patients (<50 years)
- Patients with family history
- Atypical presentations
Testing typically includes:
- MAPT haplotype analysis
- Targeted MAPT mutation screening
- Autosomal dominant inheritance for mutations
- Variable penetrance for risk alleles
- Implications for family members
- Tau-targeted therapies: Anti-tau antibodies, tau aggregation inhibitors
- Gene therapy: AAV-based MAPT silencing
- Small molecule inhibitors: Tau phosphorylation inhibitors
The study of Psp Genetic Variants has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
- Hoglinger GU, et al. Identification of common genetic risk variants for progressive supranuclear palsy. Nat Genet. 2011;43(7):699-705.
- Coppola G, et al. Evidence for a role of the rare H1 haplotype in increasing risk for PSP. JAMA Neurol. 2012;69(7):870-874.
- Boxer AL, et al. Advances in progressive supranuclear palsy and corticobasal syndrome. Nat Rev Neurol. 2014;10(10):590-598.
- Liu Y, et al. The MAPT H1 haplotype is a risk factor for PSP independent of gene expression. Acta Neuropathol Commun. 2019;7(1):8.
- Malpetti M, et al. Tau PET in progressive supranuclear palsy: association with cognitive decline and genetic risk. Neurology. 2020;95(22):e2989-e3001.