Familial risk of dementia associated with a biologic subtype of Alzheimer's disease

Meta-analysis and systematic review of peripheral platelet-associated biomarkers to explore the pathophysiology of alzheimer's disease

INTRODUCTION

Platelets are the primary peripheral reserve of amyloid precursor protein (APP), providing more than 90% of blood amyloid-beta (Aβ). Some oxidative stress markers and neurotransmitter markers were also differentially expressed in the peripheral platelets of AD. Therefore, the present study explored the differences in platelet-associated biomarkers between AD and healthy controls using meta-analysis and systematic review to reveal the value of platelet in the pathogenesis and development of AD.

METHODS

We searched all the related studies that probed into the platelets in AD based on PubMed, Embase, and web of science databases from the establishment to November 04, 2021.

RESULTS

Eighty-eight studies were included in the meta-analysis, and the platelets data of 702 AD and 710 controls were analyzed. The results of standardized mean difference (SMD) showed that platelets in AD had lower levels of APP ratio (SMD: -1.89; p < 0.05), ADAM10 (SMD: -1.16; p < 0.05), Na + -K + -ATPase (SMD: -7.23; p < 0.05), but higher levels of HMW/LMW tau (SMD: 0.92; p < 0.05), adenosine A₂ receptor (SMD: 4.27; p < 0.05), MAO-B (SMD: 1.73; p < 0.05), NO (SMD: 4.25; p < 0.05) and ONOO^- (SMD: 7.33; p < 0.05). In the systematic review, some other platelet markers seem to be meaningful in AD patients.

CONCLUSION

The results of the present meta-analysis and systematic review demonstrated that the alterations of APP metabolic enzymes, oxidative stress markers, and neurotransmitter factors in platelets were similar to their changes in the central nervous system of AD, suggesting that platelet could be a good source of peripheral biomarkers and may play an important role in the pathophysiological development of AD.

D10S1423 identifies a susceptibility locus for Alzheimer's disease (AD7) in a prospective, longitudinal, double-blind study of asymptomatic individuals: results at 14 years

Typical forms of Alzheimer's disease (AD) appear to be influenced by multiple susceptibility loci. This report describes the prospective, longitudinal, double-blind assessment of the age-specific risk of AD encountered by 325 asymptomatic first-degree relatives of AD probands who carried the D10S1423 (AD7) 234 bp allele, the APOE E4 allele, or both, after 14 years of systematic follow-up. A total of 30 incident cases of AD were detected during the first 3752 subject-years of surveillance. The effects of carrying either or both of the D10S1423 234 bp and APOE E4 alleles on the age-specific risk of developing AD were determined using Kaplan-Meier survival analysis. The risk of developing AD was the greatest for individuals who carried both alleles (Mantel-Cox statistic = 16.46, df = 3, P = 0.0009; Breslow statistic = 13.38, df = 3, P = 0.004). Cox proportional hazards models were developed to estimate the risk ratios for each genotype, controlling for the potential effects of age at recruitment, sex, and years of education. Only individuals who carried both risk alleles exhibited a risk ratio that differed significantly from 1 (risk ratio = 7.5, P = 0.002, 95% CI = 2.1-27.0). Neither age at recruitment, sex, nor years of education made significant contributions to the model, although women tended to be at greater risk (P = 0.06). Recent evidence that D10S1423 resides within open reading frame C10orf112, whose predicted product resembles a low-density lipoprotein receptor, suggests a molecular mechanism for this gene-gene interaction.

A review of the evidence from family, twin and adoption studies for a genetic contribution to adult psychiatric disorders

Family, twin and adoption studies have provided major evidence for the role of genetics in numerous psychiatric disorders including obsessive-compulsive disorder, panic disorder, major depressive disorder, bipolar disorder, schizophrenia and Alzheimer's disease. As the search for patterns of inheritance and candidate genes of these complex disorders continues, we review relevant findings from quantitative genetic studies and outline the main challenges for the field of psychiatric genetics to focus on in order to more definitively establish the underpinnings of genetic and environmental influences of adult psychopathology.

Clinical and neurobiological correlates of DXS1047 genotype in Alzheimer's disease

BACKGROUND

The goal of the current study was to explore the clinical, neuropathological, and neurochemical correlates of the DXS1047 202 bp allele in a group of 50 autopsy-confirmed cases of Alzheimer's disease (AD) who lacked other concomitant brain diseases. We previously published the results of a genome survey for novel risk loci for typical-onset (> or = 60 years) AD conducted at 10 cM resolution (Zubenko et al 1998a, b). This survey detected associations of alleles at six microsatellite loci with AD, including the 202 bp allele of the DXS1047 locus that resides within Xq25 on the human cytogenetic map.

METHODS

Clinical assessments were performed as part of a longitudinal study of AD and related disorders. Autopsies were performed using standardized methods and the resulting diagnoses were made according to established criteria. Genotyping, morphometry, and neurochemical analyses were performed using postmortem brain tissue.

RESULTS

Patients with AD who carried the DXS1047 202 bp allele manifested cortical norepinephrine levels that ranged from 2.1 to 3.6 times the corresponding values for noncarriers (p = .002), controlling for the potential effects of gender, age at symptomatic onset or death, and postmortem interval. In contrast, carriers tended to have lower cortical levels of dopamine (p = .10).

CONCLUSIONS

These findings support the results of our previous genome survey and suggest that the DXS1047 locus, or a locus in close proximity, modulates biological variables relevant to the pathophysiology of AD. In addition to providing insights into the clinical biology of AD, the characterization of biologically meaningful subtypes, including genotypic subtypes associated with particular neurobiological derangements, may be important to the advancement of experimental therapeutics in AD.

Reductions in brain phosphatidylinositol kinase activities in Alzheimer's disease

BACKGROUND

Converging lines of evidence suggest that alterations in the intracellular trafficking of the amyloid precursor protein, its derivatives, and other relevant proteins may contribute to the pathophysiology of Alzheimer's disease (AD). Since phosphatidylinositol (PI) kinase plays a pivotal role in the sorting and transport of newly synthesized proteins to their final destinations, we explored the hypothesis that AD is associated with alterations in the specific activities of these enzymes in postmortem brain tissue.

METHODS

The specific activities of soluble and particulate pools of PI 3-kinase and PI 4-kinase from the frontal cortex were compared between 11 cases with histopathologically confirmed AD and 11 nondemented controls matched for sex, race, age at death, and postmortem interval. Potential associations of these activities with sociodemographic and clinical features were also explored.

RESULTS

AD was associated with 43-59% reductions in the specific activities of the soluble forms of both lipid kinases; but no significant change in the specific activities of the particulate species. Associations of these specific activities with sex, age at onset or death, duration of illness, postmortem interval, or densities of morphologic lesions in the frontal cortex were not observed among the 11 AD cases.

CONCLUSIONS

In addition to regulating protein sorting and trafficking, PI kinases participate in a wide range of cellular processes including protection from apoptosis, differentiation and cell growth, regulation of the cytoskeleton, and glucose metabolism. The results of this study suggest that one or more of these alterations in AD may result from a common abnormality in PI kinase regulation.

Characteristics of familial aggregation in early-onset Alzheimer's disease: evidence of subgroups

Characteristics of familial aggregation of Alzheimer's Disease were studied in 92 families ascertained through a clinically diagnosed proband with an onset below age 60 years. In each family data were systematically collected on the sibships of the proband, of his father, and of his mother. A total of 926 relatives were included and 81% of the living relatives (i.e., 251 individuals) were directly examined. The estimated cumulative risk among first degree relatives was equal to 35% by age 89 years (95% confidence interval 22 to 47%). This result does not support the hypothesis that an autosomal dominant gene, fully penetrant by age 90 years, is segregating within all these pedigrees. Despite the fact that all probands were selected for an onset before age 60 years it was shown that two types of families could be delineated with respect to age at onset among affected relatives: all secondary cases with an onset below age 60 years were contributed by a particular group of families (type 1 families), whereas all secondary cases with an onset after age 60 years were contributed by another group of families (type 2 families). Although genetic interpretation of these findings is not straightforward, they support the hypothesis of etiologic heterogeneity in the determination of early-onset Alzheimer's disease.

Association of the apolipoprotein E epsilon 4 allele with clinical subtypes of autopsy-confirmed Alzheimer's disease

Consistent with previous reports, we observed a significant association of the APOE epsilon 4 allele with Alzheimer's Disease (AD) in a series of 91 autopsy-confirmed cases. The epsilon 4 allele frequency was higher in cases with a family history of AD-like dementia (0.54 +/- 0.07), although the epsilon 4 allele frequency in the AD cases with a negative family history (0.38 +/- 0.05) remained significantly greater than that for the non-AD control group (0.13 +/- 0.03). A similar increase in epsilon 4 allele frequency (0.54 +/- 0.07) was observed in the AD cases with amyloid angiopathy, compared to those who did not have amyloid angiopathy (0.36 +/- 0.04). Contrary to previous reports, no effect of the dosage of the epsilon 4 allele was found on the age of onset of dementia among the AD cases and, contrary to reports suggesting an association of epsilon 4 and atherosclerosis, the epsilon 4 allele frequency was similar in cases with or without concurrent brain infarcts. Modest but consistent correlations were observed between the dosage of epsilon 4 alleles and the cortical density of senile plaques, but not neurofibrillary tangles. The last finding suggests that the pathogenic events mediated by the epsilon 4 allele may be more directly involved in the formation of senile plaques, the identifying lesions in AD, than neurofibrillary tangles. A robust association of both the presence of an epsilon 4 allele and a family history of AD-like dementia with concurrent amyloid angiopathy occurred within our sample of AD cases. This association arose from an interaction of the epsilon 4 allele with a separate familial factor for which a family history of dementia served as a surrogate. These results suggest that amyloid angiopathy may be a common or central feature of a form of familial AD that is associated with the transmission of the APOE epsilon 4 allele.

Platelet membrane fluidity and plasma malondialdehyde levels in Alzheimer's demented patients with and without family history of dementia

Platelet membrane fluidity (PMF) was measured with three different fluorescent probes, 1,6-diphenyl-1,3,5-hexatriene (DPH), 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH), 3-(p-phenyl-1,3,5-hexatrienyl)phenyl-propionic acid (DPH-PA), which labeled different parts of the bilayer (the hydrophobic core and the positively and negatively charged regions, respectively) in Alzheimer's disease (AD) patients with and without a family history of dementia, and in a control group. In support of earlier findings in the literature, significantly increased PMF was found by the application of DPH in both groups with AD. The use of the fluorescence probe TMA-DPH, however, revealed no differences between the groups. In contrast, significant rigidification was observed with DPH-PA, but only in the AD group with a positive family history of dementia. The plasma malondialdehyde levels appeared to be similar in each group. Our findings are discussed in light of the controversies regarding the value of PMF measurements in AD.

Heterogeneity of brain gene expression in Alzheimer's disease

We have examined the expression of several genes whose transcripts have increased levels in Alzheimer's disease and have found heterogeneity in these levels in different patients with this condition. The level of expression of these genes was compared to different clinical and pathological aspects of the disease. A case with markedly elevated alpha 1-antichymotrypsin mRNA levels demonstrated prominent neuronal accumulation of this protein. Many of the neurons which demonstrated alpha 1-antichymotrypsin staining did not have neurofibrillary tangles, and vice versa. This suggests that alpha 1-antichymotrypsin staining might identify a different facet of the pathology of Alzheimer's disease than does neurofibrillary tangle staining and may provide new information in the study of this condition.

Detection of distinct isoform patterns of the beta-amyloid precursor protein in human platelets and lymphocytes

Cerebral deposition of the amyloid beta-protein (A beta P), approximately 40 residue fragment of the integral membrane protein, beta-amyloid precursor protein (beta APP), has been implicated as the probable cause of some cases of familial Alzheimer's disease (AD). The parallels between A beta P deposition in AD and the deposition of certain plasma proteins in systemic amyloid diseases has heightened interest in the analysis of beta APP in circulating cells and plasma. Here, we describe distinct isoform patterns of beta APP in peripheral platelets and lymphocytes. PCR-mediated amplification of mRNA from purified platelets demonstrated the expression of all three major beta APP transcripts (beta APP770,751,695). The full-length, approximately 140 kDa form of beta APP751,770 was detected in membranes of resting and activated platelets but very little immature, approximately 122 kDa beta APP751,770 was found, suggesting a different processing of beta APP in platelets than that described in a variety of cultured cells and tissues. Platelets stimulated with thrombin, calcium ionophore, or collagen released the soluble, carboxyl-truncated form of beta APP (protease nexin-II), but no evidence for the shedding of full-length beta APP associated with platelet microparticles was found, in contrast to previous reports. As a positive control marker for microparticles, the fibrinogen receptor subunit, GPIIIa, was readily detected in platelet releasates. Resting and activated platelets contained similar amounts of the approximately 10 kDa carboxyl terminal beta APP fragment that is retained in platelet membranes following the constitutive cleavage of protease nexin-II. Nonstimulated peripheral B and T lymphocytes contained small amounts of membrane-associated mature and immature beta APP751,770. The potentially amyloidogenic full-length beta APP molecules present in circulating platelets and lymphocytes but not in microparticles could serve as a source of the microvascular A beta P deposited during aging and particularly in AD.

Intracellular membranes are more fluid in platelets of Alzheimer's disease patients

We studied 12 patients with probable Alzheimer's disease versus age- and sex-matched healthy control subjects. Platelets were subfractionated into intracellular membranes and plasma membranes, and steady-state anisotropy of diphenylhexatriene was measured on the preparations as an index of membrane fluidity. Fluidity was higher in intracellular membranes from platelets of Alzheimer's patients compared to controls (P = 0.016). However, no difference was observed in purified plasma membrane's fluidity from the same patients versus controls. Neither the platelet counts, platelet volumes, percent of larger platelets, nor the amount of internal membrane protein per platelet were different between groups. There was no correlation between intracellular membrane anisotropy and severity of dementia as measured on the Mini-Mental State Exam. The results extend previous studies suggesting that there is an intracellular membrane alteration in platelets in Alzheimer's disease.

Risk factors for stroke as predictors of platelet membrane fluidity in Alzheimer's disease

We have previously reported that increased platelet membrane fluidity identifies a subgroup of patients with Alzheimer's disease who have distinct clinical features including an earlier age of symptomatic onset, a more rapidly progressive cognitive decline, and a decreased prevalence of focal electroencephalographic findings. In the current study, these patients also exhibited a decreased prevalence of risk factors for stroke compared with patients who had normal platelet membrane fluidity. Our findings suggest that the platelet membrane abnormality describes a clinical subgroup of patients with Alzheimer's disease who are less likely to have coexisting cerebrovascular disease than the remaining patients who meet clinical consensus criteria for probable Alzheimer's disease.

Platelet phospholipid synthesis in Alzheimer's disease

The rates of incorporation of [3H]choline and [3H]ethanolamine into membrane phospholipids of platelets from 22 drug-free Alzheimer's disease patients and 18 normal elderly controls were compared. No significant differences between groups were found. If alterations in lipid metabolism are involved in the pathophysiological processes underlying Alzheimer's disease, such alterations are not manifest in measures of radiolabeled base incorporation into platelet phospholipids.

Heterogeneity in Alzheimer's disease: evidence from cellular radiosensitivity and complementation of this phenotype

Radiosensitivity was studied in a series of Alzheimer's disease (AD) patients and normal controls by examining clonogenic survival and radiation-induced chromosome aberrations in lymphoblastoid cell lines. D0 values based on colony survival for AD and normals following exposure to gamma-rays were 0.86 +/- 0.04 and 1.14 +/- 0.03 Gy respectively. However, 2 of the AD cell lines had D0 values in the normal range. This increased radiosensitivity in AD cells was confirmed by an increased number of gamma-ray-induced chromosome aberrations in these cells. Cell fusion was employed to investigate the presence of different complementation groups for the radiosensitive phenotype in AD using frequency of radiation-induced chromosome aberrations as a means of distinguishing different groups. Four complementation groups were found among 5 AD cell lines. These findings provide additional experimental evidence in support of heterogeneity in AD.

SOD-1 activity and platelet membrane fluidity in Alzheimer's disease

An early-onset, familial form of Alzheimer's disease (AD) has been reported to be linked to a locus on the long arm of chromosome 21 (21q21). Furthermore, duplications in the vicinity of this locus involving the beta-amyloid gene and the proto-oncogene ets-2 have been reported in association with AD. The structural gene for Cu,Zn superoxide dismutase, SOD-1, is located between the beta-amyloid gene and ets-2. For this reason and because SOD-1 is a plausible candidate for a gene that might influence the fluidity of cellular membranes, we determined whether or not the subtype of AD with increased platelet membrane fluidity was associated with an increase in Cu,Zn superoxide dismutase activity.

Endoplasmic reticulum abnormality in Alzheimer's disease: selective alteration in platelet NADH-cytochrome c reductase activity

Previous evidence suggests that the increase in platelet membrane fluidity associated with a subgroup of patients with Alzheimer's disease results from the accumulation of internal membrane. The specific activities of enzyme markers for selective cell membrane compartments were compared in platelets from subgroups of demented patients with normal or increased fluidity as well as from normal control subjects. A statistically significant change in enzyme activity was observed only for antimycin A-insensitive NADH-cytochrome reductase, a selective marker for smooth endoplasmic reticulum (SER) in platelets. This reduction was limited to the subgroup of demented patients who had increased platelet membrane fluidity, and therefore is not a nonspecific concomitant of neurodegeneration, medication exposure, or chronic illness in general. Since the platelet membrane alteration associated with Alzheimer's disease results from the inheritance of a single major locus, these results suggest that a defect in SER function may exist in brain cells as well as peripheral cells that express this genotype.

Criteria for onset critically influence the estimation of familial risk in Alzheimer's disease

The rare early-onset variant of Alzheimer's disease (AD) appears to be transmitted as an autosomal dominant genetic trait. More typical late-onset AD also shows familial aggregation, but possible genetic mechanisms are difficult to examine because the phenotypic expression of the putative AD genotype is often censored by prior death from competing causes. Lifetable methods have been used to examine the age-specific risk of dementia among relatives, and thus to test the hypothesis of genetic transmission of late-onset AD. These methods require the ascertainment of affected relatives and the determination of their age at onset. The latter determination is somewhat arbitrary, since symptoms of AD evolve and develop in a continuous and progressive fashion, and different workers may thus use differing criteria for "onset." This paper demonstrates that the use of divergent thresholds for "caseness" (typically, progressive dementia of several years' duration) and onset (e.g., the first appearance of mild cognitive symptoms, or the first clear evidence of dementia) can introduce substantial bias toward underestimation of risk among relatives. Depending on the definition of onset, familial risk may be underestimated, with apparent cumulative incidence decreased to only 60% of values otherwise expected. We suggest that this problem can be avoided by the use of identical threshold criteria for caseness and for onset.

Genetic studies on an Alzheimer clinic population

All patients attending the Clinic for Alzheimer Disease and Related Disorders have detailed family histories taken by a geneticist. To date, genetic histories are available for 446 consecutive, unrelated individuals. Of these, 151 (33.9%) are diagnosed as having "probable" (N = 141) or "autopsy-confirmed" (N = 10) Alzheimer disease according to recognized criteria. This data base represents a relatively unselected population with respect to more than one person in the family having dementia. Seventy-one of these 151 index cases (47.0%) have a positive family history of dementia, of which 8 (5.3%) may represent the familial (autosomal dominant) form of Alzheimer disease (FAD). Age-corrected empiric recurrence risks for Alzheimer disease/dementia were calculated for first-degree relatives of these 151 index cases using the Kaplan-Meier lifetable method.

Markedly increased platelet membrane fluidity in Down syndrome with a (14q, 21q) translocation

Abnormal platelet membrane fluidity was found in a 50-year-old woman with Down syndrome who had been experiencing a gradual mental decline. The patient's karyotype showed a triplication of the long arm of chromosome 21. The authors hypothesize that the PMF-locus, which carries the allele for increased membrane fluidity, is located on the long arm of chromosome 21. Similarities between Down syndrome and Alzheimer's disease and the possible relationship between membrane fluidity and cognitive function are mentioned.