Mutations of three different genes-amyloid precursor protein (APP), presenilin 1 (PS-1), presenilin 2 (PS-2)-have been found in early-onset autosomal dominant forms of AD, of the human microtubule associated-protein tau gene (MAPT) in frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), of the BRI gene in familial British dementia, of the PI12 gene in familial encephalopathy with neuroserpin inclusion bodies.
Presenilin 1 (PSEN1) gene mutations deterministic for Alzheimer's disease (AD) are associated with marked heterogeneity in clinical phenotype, with behavioral and psychiatric features, parkinsonism, myoclonus, epileptic seizures, spastic paraparesis, frontal behavioral changes suggestive of the phenotype of frontotemporal dementia, aphasia, and cerebellar ataxia being described as well as cognitive decline.
We investigated the contribution of rare variants in seven genes of known relevance to dementias (β-amyloid precursor protein (APP), PSEN1/2, MAPT (microtubule-associated protein tau), fused in sarcoma (FUS), granulin (GRN) and TAR DNA-binding protein 43 (TDP-43)) to PD and PD plus dementia (PD+D) in a discovery sample of 376 individuals with PD and followed by the genotyping of 25 out of the 27 identified variants with a minor allele frequency <5% in 975 individuals with PD, 93 cases with Lewy body disease on neuropathological examination, 613 individuals with Alzheimer's disease (AD), 182 cases with frontotemporal dementia and 1014 general population controls.
Genetic testing confirmed the absence of mutations in the presenilin 1 gene in 1 patient; subsequent testing revealed the R406W tau mutation in both individuals leading to a diagnosis of frontotemporal dementia [F]FDDNP retention broadly correlated with CSF levels of t-tau and p-tau.
Thirty brain regions were examined in argyrophilic grain disease (AGD; n = 5), tangle-predominant senile dementia (TPSD; n = 5), Pick disease (n = 4), familial AD (FAD; n = 2; PSEN1p.G206A and p.S170P), and frontotemporal dementia with parkinsonism linked to chromosome-17 (FTDP-17; n = 2; MAPT p.P301L and IVS10 + 16).
We screened 37 AD, 8 mild cognitive impairment (MCI), 3 AD and CVD (cerebrovascular disease), 3 MCI and CVD, 8 frontotemporal dementia (FTD) and 2 progressive supranuclear palsy (PSP) patients, and 28 normal controls (NCs).We sequenced PSEN1, PSEN2 and APP (EOAD risk factors), as well as MAPT, GRN and TARDBP for all cases and NCs, and analysed the APOE, CLU, CR1 and PICALM genotypes as well as the MAPT and ACE haplotypes (LOAD risk factors) for the AD (n = 37) and AD + MCI (n = 45) cases and NCs (n = 28).We identified variants in PSEN1, PSEN2 and TARDBP across a range of phenotypes (AD, AD and CVD, FTD and PSP), suggesting that screening of all known candidate genes of Alzheimer's and non-Alzheimer's forms of dementias in all dementia cases might be warranted.
The 3 × Tg-AD mouse simultaneously expresses 3 rare familial mutant genes that in humans independently produce devastating amyloid-β protein precursor (AβPP), presenilin-1, and frontotemporal dementias; hence, technically speaking, these mice are not a model of sporadic AD, but are informative in assessing co-evolving amyloid and tau pathologies.