Increased amyloid , 8-peptide deposition in cerebral cortex as a consequence of apolipoprotein E genotype in late-onset Alzheimer disease ( phenotype / APOE 4 gene )

Amyloid -peptide (AP) deposition in senile plaques and cerebral vessels is a neuropathological feature of Alzheimer disease (AD). We examined the possibility that commonly observed variability in Af8 deposition in late-onset AD might be related to apolipoprotein E genotype (APOE gene; the two most common alleles are 3 and 4), since APOE4 is a susceptibility gene for late-onset AD and apolipoprotein E interacts strongly with A.8 in vitro. In an autopsy series of brains of late-onset AD patients, we found a strong association of APOE4 allele with increased vascular and plaque Af3 deposits. Late-onset AD patients with one or two APOE4 alleles have a distinct neuropathological phenotype compared with patients homozygous for APOE3. Amyloid deposition in cerebral vessels and in senile plaques is one of the recognized neuropathological features of both earlyand late-onset Alzheimer disease (AD) (1-3). A major component of these amyloid deposits is the f-peptide (AP3) fragment of amyloid precursor protein (APP, protease nexin II, encoded on chromosome 21) (4-11). The role of A/3 and APP in the pathogenesis of certain cases of early-onset AD is supported by the association of specific point mutations in APP with rare examples of autosomal dominant early-onset familial AD (12-16). In the much more common cases of late-onset AD, a direct role of A,8 and APP in the pathogenesis of AD is less likely. APP mutations have not been identified in sporadic and familial late-onset AD, and genetic linkage for late-onset AD has been excluded on chromosome 21 (17, 18). In addition, the degree of amyloid deposition in late-onset AD, particularly for cerebral vessels, can vary widely from case to case (18-22). We have recently provided evidence that apolipoprotein E (apoE) allele E4 (APOE4 gene; located on chromosome 19) is a susceptibility gene or risk factor in both sporadic and familial late-onset AD (23-25) and is inherited as an autosomal codominant trait. The possible involvement of apoE in late-onset AD is based on several findings in addition to the reported increase of APOE4 gene frequency (23, 24). apoE appears to play an important role in nerve cell injury and regeneration (26). The role of apoE isoforms in neuronal injury may involve not just facilitation of cholesterol transport but also interactions that result in targeting or sequestering of proteins (27). Furthermore, apoE is found in close association with amyloid deposits in vessels and plaques in AD as well as in other amyloidoses such as CreutzfeldtJakob disease and kuru (23, 28, 29). A specific role for apoE in AD-related pathology is suggested by the high-avidity The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. binding ofapoE isoforms in vivo with A, and the significantly different binding characteristics of the apoE4 isoform with A,B compared with the apoE3 isoform (30, 31). To test whether APOE genotype might be associated with a distinctive neuropathological phenotype, we examined the extent of amyloid deposition in autopsy-confirmed cases of sporadic late-onset AD in patients with defined APOE genotype, using routine neuropathological reports and examination of Congo redand immunostained slides. We found that patients with sporadic late-onset AD who have one or two copies of APOE4 have a distinctive neuropathological phenotype of greatly increased vascular and plaque amyloid deposits compared with patients homozygous for APOE3. MATERIALS AND METHODS Case Selection andAPOE Genotyping. Frozen and formalinfixed material from 143 patients with autopsy-confirmed cases of late-onset AD without affected family members and without other neurological disease in the period 1985-1992 was obtained through the Kathleen Bryan Brain Bank at Duke University. All cases satisfied National Institutes of Health and Consortium to Establish a Registry for Alzheimer's Disease criteria (1, 2). APOE genotyping for each patient was carried out as previously described, using amplification by polymerase chain reaction (24, 32, 33). Neuropathological Analysis. Information on age at death, apparent duration of illness, gender, brain weight, mention of amyloid deposits in cerebral vessels (Congo red stain), and description of number of neuritic plaques (69 cases) and neurofibrillary tangles (95 cases) from modified King's silverstained sections (34) were taken from the original neuropathological reports. Each count represented a single microscopic field felt to be the most affected area in that tissue section; a lOx objective was used for plaques (field of 2.92 mm2) and a 20x objective for tangles (field of 0.72 mm2). Counts were truncated at 100 per field. Analysis of Congo Red-Stained Material for Vascular Amyloid. A subset of 53 patients was chosen by selecting in chronological order those cases for which Congo red-stained slides had previously been prepared. Forty of the 53 autopsy reports specifically mentioned vascular amyloid and formed one set ofblinded observations completed before genotyping. Mention of vascular amyloid was graded as follows: no evident amyloid deposits, grade 0; trace amyloid deposits including one positive vessel, grade 1; and readily identifiable vascular amyloid, grade 2. In addition, a single Congo red-stained slide of frontal cortex and of hippocampus from each of the 53 patients was examined double-blind for extent Abbreviations: AD, Alzheimer disease; A,B, amyloid 3-peptide; APP, amyloid precursor protein.