Our results may suggest that late-onset FAD has at least 2 etiologies; AD in some families may be transmitted as a dominant trait, whereas a proportion of cases in these and other late-onset families may be caused by other genetic or shared environmental factors.
Because we have recently cloned a novel gene S182 bearing five different missense mutations which segregate with early-onset familial AD, we sought the frequency of these mutations in familial and sporadic late-onset AD to clarify the incidence of these mutations in the disease.
We compared immunohistochemical expression of the transforming growth factor-betas (TGF-beta 1, TGF-beta 2, and TGF-beta 3) using brain tissue from patients with nondominantly inherited Alzheimer's disease (NDAD) (n = 9), autosomal dominantly inherited Alzheimer's disease with linkage to 14q24.3 (FAD-14) (n = 4), and cognitively normal controls (n = 10) to determine whether their pathologic changes are associated with an altered distribution of the TGF-betas.
As families AD/A and AD/B have very similar AD phenotype our observation of two mutations in functionally different domains suggest that onset age and severity of AD may not be very helpful predictors of the location of putative S182 mutations.
There were no significant differences between PS-1 mRNA levels per pg total RNA in mid-temporal or superior frontal cortices of the Alzheimer's disease subjects, compared to controls.
Recent studies suggest that mutations in the presenilin 1 gene, which encodes a polypeptide predicted to be a multispanning membrane protein, are responsible for the majority of cases of early onset, autosomal dominant Alzheimer's disease.
Secreted amyloid beta-protein similar to that in the senile plaques of Alzheimer's disease is increased in vivo by the presenilin 1 and 2 and APP mutations linked to familial Alzheimer's disease.
To obtain in vivo information about how PS1 mutations cause AD pathology at such early ages, we characterized the neuropathological phenotype of four PS1-FAD patients from a large Colombian kindred bearing the codon 280 Glu to Ala substitution (Glu280Ala) PS1 mutation.
The final identification of PS-1 as the causal gene for Alzheimer's disease (AD) was concluded based on finding of the point mutations in the candidate cDNA linked with pedigrees with early-onset familial AD.
The presenilin 1 gene has recently been identified as the locus on chromosome 14 which is responsible for a large proportion of early onset, autosomal dominantly inherited Alzheimer's disease (AD).
Linkage analyses have implicated several genes as causes or risk factors for Alzheimer's disease in different families: the amyloid precursor protein gene, the apolipoprotein-E gene (E4 subtype) on chromosome 19, the S182 gene on chromosome 14 and the STM2 gene on chromosome 1.
Therefore, (one of) the effects of the mutations in the presenilin 1:PS-1 (S182) gene may be to cause or at least promote an early and excessive deposition of Abeta42(43) within the brain, a property shared with other inherited forms of AD, such as those due to amyloid precursor protein mutations, and Down's syndrome (trisomy 21).
Comparison of the disease phenotypes associated with other missense mutations in exon 9 of PS-1 reveals no clinical or pathological phenotype, which uniquely distinguishes Alzheimer's disease associated with PS-1 mutations from other forms of early-onset FAD, implying that direct mutation screening is required to identify these cases.
Furthermore, the amounts of PSNL1 mRNA in neurofibrillary tangle (NFT)-bearing neurons and those without NFTs did not differ, and the clinical severity of AD was not related to PSNL1 mRNA expression level.
Homozygosity for the 'T' allele of a polymorphism in the presenilin 1 gene has previously been reported to double the risk for Alzheimer's disease in a late onset Caucasian sample.
This study shows that both APP mRNA and protein are induced in lymphoblastoid cell lines following heat shock and that this response is not affected by PS-1 mutations which are pathogenic for Alzheimer's disease.