Apolipoprotein E allele in Chamorros with amyotrophic lateral sclerosis/parkinsonism-dementia complex

Role of apolipoprotein E polymorphism as a prognostic marker in traumatic brain injury and neurodegenerative disease: a critical review

OBJECT

The difference in course and outcome of several neurodegenerative conditions and traumatic injuries of the nervous system points toward a possible role of genetic and environmental factors as prognostic markers. Apolipoprotein E (Apo-E), a key player in lipid metabolism, is recognized as one of the most powerful genetic risk factors for dementia and other neurodegenerative diseases. In this article, the current understanding of APOE polymorphism in various neurological disorders is discussed.

METHODS

The English literature was searched for various studies describing the role of APOE polymorphism as a prognostic marker in neurodegenerative diseases and traumatic brain injury. The wide ethnic distribution of APOE polymorphism was discussed, and the recent meta-analyses of role of APOE polymorphism in multiple diseases were analyzed and summarized in tabular form.

RESULTS

Results from the review of literature revealed that the distribution of APOE is varied in different ethnic populations. APOE polymorphism plays a significant role in pathogenesis of neurodegeneration, particularly in Alzheimer’s disease. APOE ε4 is considered a marker for poor prognosis in various diseases, but APOE ε2 rather than APOE ε4 has been associated with cerebral amyloid angiopathy-related bleeding and sporadic Parkinson’s disease. The role of APOE polymorphism in various neurological diseases has not been conclusively elucidated.

CONCLUSIONS

Apo-E is a biomarker for various neurological and systemic diseases. Therefore, while analyzing the role of APOE polymorphism in neurological diseases, the interpretation should be done after adjusting all the confounding factors. A continuous quest to look for associations with various neurological diseases and wide knowledge of available literature are required to improve the understanding of the role of APOE polymorphism in these conditions and identify potential therapeutic targets.

Apolipoprotein E and central nervous system disorders: reviews of clinical findings

Dementia is a major health problem in developed countries with over 25 million people affected worldwide and probably over 75 million people at risk during the next 20 years. Alzheimer's disease (AD) is the most frequent cause of dementia (50-70%), followed by vascular dementia (30-40%), and mixed dementia (15-20%). AD pathogenesis is still to be elucidated but it is believed to be the complex interaction between genetic and environmental factors in later life. Three causative genes for familial AD have been identified: amyloid precursor protein, presenilin-1, and presenilin-2. There are 150 genes involved with increased neuronal vulnerability to premature death in the AD brain. Among these susceptibility genes, the apolipoprotein E (ApoE) gene is the most prevalent as a risk for AD pathogenic process in which complex interactions between genetic and environmental factors are involved, leading to a cascade of pathogenic events converging in final pathways to premature neuronal death. Some of these mechanisms are common to several neurodegenerative disorders that differ depending upon the genes affected and the involvement of environmental conditions. ApoE is a key lipoprotein in lipid and cholesterol metabolism and it is also the major risk gene for AD and many other central nervous system disorders. The pathogenic role of ApoE-4 is still to be clarified; however, diverse evidence suggests that ApoE may play pleiotropic functions in dementia and central nervous system disorders.

Genetic epidemiology of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a late onset, rapidly progressive and ultimately fatal neurological disorder, caused by the loss of motor neurons in the brain and spinal cord. Familial aggregation of ALS, with an age-dependent but high penetrance, is a major risk factor for ALS. Familial ALS (FALS) is clinically and genetically heterogeneous. Three genes and linkage to four additional gene loci have been identified so far and may either predominantly lead to ALS (ALSI-ALS6) or cause multisystem neurodegeneration with ALS as an occasional symptom (tauopathies, ALS-dementia complex). This review presents a tentative classification of the "major" ALS genes and ALS "susceptibility" genes, that may act as susceptibility factors for neurodegeneration in interaction with other genetic or environmental risk factors. Considering that mutations in ALS genes explain approximately 10% of familial as well as sporadic ALS, and most remaining cases of the discase are thought to result form the interaction of several genes and environmental factors, ALS is a paradigm for multifactorial discases.

Apolipoprotein E and multiple sclerosis: a biochemical and genetic investigation

Apolipoprotein E (apo E) is postulated to be a major lipid carrier protein in the brain involved in brain development and repair. Multiple sclerosis (MS) is a major demyelinating disease characterized by destruction of myelin and marked alteration of myelin cholesterol and lipid metabolism. We have determined serum and cerebrospinal fluid (CSF) apo E concentrations using an original time-resolved immunofluorometric assay and calculated intrathecal apo E concentration. Apo E concentrations were determined in 13 control subjects and 129 neurological patients: 34 definite MS patients, 25 with Guillain-Barré syndrome (GBS), 32 with amyotrophic lateral sclerosis (ALS) and 38 with other neurological diseases. Seven clinical parameters (sex, age, age at MS onset, duration of the disease, course, clinical status and disability score) were considered in MS patients. Significant (P < 0.01) decrease in CSF apo E was observed in MS, linked to a decrease in intrathecal apo E. The decreased CSF apo E concentration in MS patients occur independent of the apo E genotype. Apo E is considered as a neurotrophic factor in the brain. Any decrease in intrathecal apo E synthesis would thus contribute to progression of neurological diseases, such as MS.

Apolipoprotein E genotyping in patients with neurodegenerative diseases

OBJECTIVES

There is a growing demand to perform apolipoprotein E (Apo-E) genotyping on neuropathologic archive material. Due to the extremely long fixation time, this material is unsuitable for routinely used Apo-E genotyping methods. We present an investigation into the applicability of a new method.

DESIGN AND METHODS

An Apo-E genotyping method was tested for use on formalin-fixed paraffin-embedded brain tissue, using semi-nested PCR followed by hybridization with biotin-labeled allele-specific oligonucleotides, and chemiluminescent detection. The method was applied to 88 archive samples of different neurologic disorders.

RESULTS

With this technique 76% (67/88) of the samples could be genotyped. The crucial step is the semi-nested PCR. All the samples from which a PCR product could be obtained, the Apo-E gene could be genotyped without interpretation problems. Seventy-six percent of the samples that could not be genotyped, were fixed in unbuffered formalin.

CONCLUSIONS

This technique offers a good Apo-E genotyping method applicable on neuropathological archive material in order to support in retrospect clinical studies.

Apolipoprotein E4 (ApoE4) but not ApoE3 or ApoE2 potentiates beta-amyloid protein activation of complement in vitro

Apolipoprotein E4 (ApoE4) increases the risk of late-onset Alzheimer's disease (AD). It binds tightly to beta-amyloid protein (A beta), which is known to activate the classical complement pathway in vitro. Since complement activation is a possible mechanism for promoting inflammation in AD, we tested, utilizing ELISA techniques, whether the various isoforms of ApoE could influence A beta complement activation, or could themselves activate the pathway. A beta applied alone to ELISA plate wells at concentrations of 100-500 ng showed a linear increase in ability to activate serum complement, but all the ApoE isoproteins were inactive. When 200 or 430 ng of A beta were plated and then exposed to solutions of 100-200 ng of ApoE2, ApoE3, ApoE4 or bovine serum albumin (BSA), only ApoE4 significantly enhanced the activation. This ApoE4-specific enhancement of complement activation by A beta may relate to its role in increasing the risk of late-onset AD.

The effect of apolipoprotein E genotype on expression of an autosomal dominant schizophreniform disorder with progressive dementia and neurofibrillary tangles

The apolipoprotein E (APOE) epsilon 4 allele is associated with an increased and the epsilon 2 allele a decreased risk for Alzheimer's disease (AD). It has been hypothesized that these risks are mediated by differential effects of the APOE alleles on the cytoskeletal degeneration, which results in neurofibrillary tangle (NFT) formation. It has also been suggested that APOE alleles differentially affect the beta amyloid accumulation. We examined APOE genotypes and their effects on age of onset in a family with an autosomal dominant "neurofibrillary tangle only" dementia. This disorder is manifested by schizophreniform psychosis followed by progressive dementia and neuropathologically by prominent AD-like neurofibrillary tangles without neuritic plaques. The only affected epsilon 4 heterozygote in this family did not demonstrate accelerated disease onset. In contrast, the affected epsilon 2 heterozygote had the latest age of onset of any affected family member. The two other epsilon 2 heterozygotes remained unaffected at an age much greater than the mean age of onset for the disease. These results are consistent with a protective effect of the epsilon 2 allele in a hereditary neuropsychiatric disorder with prominent NFT formation.

Predictive value of APOE genotyping in incipient Alzheimer's disease

The Mayo Alzheimer's Disease Center/Alzheimer's Disease Patient Registry is a prospective, longitudinal project of aging and dementia in a community setting. Over 400 pairs of individuals have been studied through this project, and extensive data on clinical, radiological, neuropathological, and biological variables have been gathered. Previous case-control studies on this group of subjects have documented the role of the apolipoprotein E (APOE) epsilon 4 as a risk factor for dementia. Subsequent analyses between APOE and the age of the patients with dementia have shown that most of the epsilon 4 effect is manifest in subjects under 75 years of age. We have also used this patient resource to study a group of individuals who are at risk for dementia by virtue of having a significant memory impairment. We have designated these patients as having a mild cognitive impairment because they have abnormal memory function but do not reach criteria for dementia. Over the course of several years of follow-up, these subjects evolve to dementia at a rate of approximately 15% per year. The presence of an APOE epsilon 4 carrier status is the best predictor of subsequent development of dementia in these individuals. These studies indicate that APOE is an important risk factor for AD, and in patients with a mild cognitive impairment, APOE may be useful in predicting who is likely to progress to dementia.

ApoE2 allele, Down's syndrome, and dementia

All individuals with Down's syndrome (trisomy 21-DS) develop the pathogenic hallmarks of Alzheimer's disease in old age (+40 years). The extent of pathology is variable, but it has been shown that the amount of beta-amyloid pathology is variable and related to age and the degree of dementia. Thus, in DS, growing old is associated with a progressive pathological process which results in cognitive decline. However, neuropsychological studies of older DS subjects have identified a clinical dementia in only a proportion of cases. These contradictory observations could be reconciled if some factor existed which modulated the rate and amount of beta-amyloid pathology. Recent studies demonstrate an association between the apolipoprotein E4 (ApoE4) allele and the earlier age of onset in both sporadic and familial AD. Increased amounts of beta-amyloid pathology can also be related to the E4 allele. However, at present there are no data documenting the effects of ApoE genotype on the expression or degree of clinical symptoms of the disease. We have examined the ApoE genotype in a cohort of clinically evaluated elderly patients with DS in order to examine the effects of ApoE genotype on the clinical symptoms of dementia. We report here that, despite the presence of an active disease process, the ApoE E2 allele is associated with longevity and preservation of cognitive functioning.

Apolipoprotein E in the genetics and epidemiology of Alzheimer's disease

The role of apolipoprotein E (ApoE) alleles and isoforms in the etiology and pathogenesis of Alzheimer's disease is discussed. The possibility that ApoE itself is not involved in the disease pathogenesis but is merely in genetic disequilibrium with the real locus is discussed and dismissed. The data showing that the epsilon 4 allele is associated with an increased risk of developing the disease and with an earlier onset age are reviewed. The data showing that, at least in some circumstances, the epsilon 2 allele is associated with a decrease in the risk of developing the disease, and with a later onset age are also reviewed. Data from the genetic analysis of other disorders are reviewed and presented, and it is suggested that the genetic data support the notion that the role of ApoE in the etiology of the disease directly relates to beta-amyloid deposition and plaque formation. This suggestion is in concordance with the most likely mechanism for the role of beta-amyloid precursor protein gene mutations as other risk factors for the disease.

Apolipoprotein E epsilon 4 allele is not associated with earlier age at onset in amyotrophic lateral sclerosis

Apolipoprotein E allele 4 (apo E epsilon 4) is known to be in genetic disequilibrium with Alzheimer's disease and is associated with an earlier age at onset of dementia. Whether apo E epsilon 4 is a specific risk factor for Alzheimer's disease or is a more general susceptibility factor that shifts the age at onset of neurodegenerative diseases to earlier ages is unknown. To test these possibilities, we determined the apolipoprotein E genotypes of subjects with familial or sporadic amyotrophic lateral sclerosis (ALS). ApoE allele frequencies of the apoE gene of the ALS subjects (n = 170, epsilon 2 = 0.071, epsilon 3 = 0.771, epsilon 4 = 0.159) were found to be comparable to the allele frequencies of the general population. Furthermore, no significant association was observed between the age at onset or the duration of ALS and the inheritance of apoE epsilon 4: subjects with at least one copy of epsilon 4 (sporadic ALS: n = 15, onset at 57.7 +/- 13.9 years; familial ALS: n = 23, onset at 53.6 +/- 9.5 years, duration [n = 14] of 2.6 +/- 1.6 years) had comparable ages at onset and durations to subjects without epsilon 4 (sporadic ALS: n = 28, onset at 53.1 +/- 17.0 years; familial ALS: n = 56, onset at 50.8 +/- 12.1 years, duration [n = 30] of 1.9 +/- 0.8 years). The lack of association of apoE epsilon 4 with the age at onset and the duration of ALS suggests that apoE epsilon 4 does not have a global effect on the pathogenesis of other neurodegenerative diseases.

Apolipoprotein E genotype in diverse neurodegenerative disorders

While the apolipoprotein E (ApoE) epsilon 4 allele is a recognized risk factor for Alzheimer's disease (AD), an association of epsilon 4 with other neurodegenerative diseases (NDs) has not been extensively explored. We examined 51 cases of neuropathologically confirmed ND. After eliminating 18 cases exhibiting pathology sufficient to warrant an additional diagnosis of AD, three disorders characterized by tau-related cytoskeletal pathology, i.e., Pick's disease, corticobasal degeneration, and progressive supra-nuclear palsy, showed increased epsilon 4 frequencies. Since the number of cases within each category was small, these increased epsilon 4 frequencies were not statistically significant. beta-Amyloid (beta A4) immunoreactive diffuse plaques were observed in many of these cases. While we cannot eliminate the possibility that these patients were destined to develop AD, these changes may merely reflect an independent association of epsilon 4 with amyloid deposition. These preliminary data affirm the need for further study of well-characterized cases to explore the relationship of ApoE to cytoskeletal pathology and ND.