Phenotype of chromosome 14-linked familial Alzheimer's disease in a large kindred

Amyloid beta protein (Abeta) deposition in chromosome 14-linked Alzheimer's disease: predominance of Abeta42(43)

Amyloid beta protein (Abeta) deposition was investigated in the frontal cortex of 8 cases of (genetically confirmed) chromosome 14-linked Alzheimer's disease (AD) using the end-specific monoclonal antibodies BA27 and BC05 to detect the presence of Abeta40 and Abeta42(43), respectively. In all patients, Abeta42(43) was the predominant peptide species present. The total amount of Abeta40 and Abeta42(43) deposited was more than twice the amount deposited in cases of sporadic AD of similar disease duration, although the ratio between the extent of Abeta40 and Abeta42(43) deposition was unaltered, compared with sporadic AD. 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).

Apolipoprotein E-epsilon 4 allele and familial risk in Alzheimer's disease

Recent studies have found an association between presence of apolipoprotein E (APOE) epsilon 4 allele and Alzheimer's disease (AD). The present study compared the cumulative risk of primary progressive dementia (PPD) in relatives of AD probands carrying at least one copy of the epsilon 4 allele with the relatives of AD probands not carrying epsilon 4 and with relatives of non-demented controls. Our aim was to determine whether the familial aggregation of PPD in relatives of AD probands is primarily due to those carrying epsilon 4. Seventy-seven neuropathologically diagnosed AD patients were obtained as probands through our Alzheimer's Disease Research Center Brain Bank. AD probands were genotyped for APOE. As a comparison group, 198 non-demented probands were also included. Through family informants, demographic and diagnostic data were collected on 382 first-degree relatives (age > or = 45 years) of AD probands and 848 relatives of the controls. We found that the cumulative risk of PPD in both relatives of AD probands with and without the epsilon 4 allele was significantly higher than that in the relatives of non-demented controls. However, the increased risk in the relatives of AD probands with the epsilon 4 allele was marginally, but not significantly, lower than the risk in the relatives of probands without epsilon 4. A greater likelihood of death by heart diseases over developing PPD in relatives of AD probands with epsilon 4 (3.1-fold increase) was found compared to relatives of probands without epsilon 4 (1.7-fold increase), especially prior to age 70, although the difference was not statistically significant. The increased familial risk for PPD in the relatives of AD probands with the APOE-epsilon 4 allele relative to controls suggests that familial factors in addition to APOE-epsilon 4 are risk factors for AD. Differential censorship from increased mortality of heart diseases may have prevented a higher incidence of PPD among the relatives of probands with epsilon 4.

Genetic dissection of Alzheimer disease, a heterogeneous disorder

The genetics of Alzheimer disease (AD) are complex and not completely understood. Mutations in the amyloid precursor protein gene (APP) can cause early-onset autosomal dominant AD. In vitro studies indicate that cells expressing mutant APPs overproduce pathogenic forms of the A beta peptide, the major component of AD amyloid. However, mutations in the APP gene are responsible for 5% or less of all early-onset familial AD. A locus on chromosome 14 is responsible for AD in other early-onset AD families and represents the most severe form of the disease in terms of age of onset and rate of decline. Attempts to identify the AD3 gene by positional cloning methods are underway. At least one additional early-onset AD locus remains to be located. In late-onset AD, the apolipoprotein E gene allele epsilon 4 is a risk factor for AD. This allele appears to act as a dose-dependent age-of-onset modifier. The epsilon 2 allele of this gene may be protective. Other late-onset susceptibility factors remain to be identified.