The MAPT gene exists in two major haplotypes—H1 and H2—defined by an inversion of a 900 kb genomic region at 17q21.31[1]. The H1 haplotype is strongly associated with increased risk of sporadic 4R-tauopathies including Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD), and Argyrophilic Grain Disease (AGD)[2].
| Feature | H1 Haplotype | H2 Haplotype |
|---|---|---|
| Genomic Structure | Non-inverted (ancestral) | Inverted genomic segment |
| Population Frequency | ~75% (European) | ~25% (European) |
| 4R Tau Expression | Upregulated | Baseline |
| Tauopathy Risk | Increased | Baseline/reduced |
PSP shows the strongest association with the MAPT H1 haplotype, with nearly universal H1 homozygosity in sporadic cases.
CBD shows similar but slightly weaker H1 association compared to PSP[3].
AGD shows a more modest H1 association than PSP or CBD[4].
GGT shows intermediate H1 association with limited available data.
Pathogenic MAPT mutations are fully penetrant regardless of haplotype. However, H1 may accelerate disease onset in mutation carriers. Different subhaplotypes interact with various mutations to modify phenotype.
Beyond H1/H2, finer genetic substructure exists within the MAPT locus:
| Subhaplotype | Key Variants | Functional Implications |
|---|---|---|
| H1a | rs246408 (A), rs2471738 (T) | Baseline risk |
| H1b | rs246408 (G), rs2471738 (C) | Modified splicing |
| H1c/H1P | rs8070723, rs242557 | Highest PSP risk |
Subhaplotypes differ in their effects on:
Baker et al. Association of an extended haplotype in the tau gene with progressive supranuclear palsy (1999). 1999. ↩︎
Sala Frigerio et al. The MAPT H1 haplotype is a risk factor for tauopathies: meta-analysis (2021). 2021. ↩︎
Taga et al. Association of MAPT haplotypes with progressive supranuclear palsy in a US cohort (2021). 2021. ↩︎
Zeithmann et al. H1 haplotype of MAPT and the risk of argyrophilic grain disease (2020). 2020. ↩︎
Vandrovcova et al. Differential association of the MAPT H1 subhaplotype with neurodegenerative diseases (2019). 2019. ↩︎