Genetic linkage evidence for a familial Alzheimer's disease locus on chromosome 14

Alzheimer's disease: a review of recent findings

The recent development of biological research on dementias of the Alzheimer's type has lead to a better understanding of their pathophysiology. We know the nature of the proteins present in senile plaques and in the neurofibrillary degeneration. Pathophysiological hypotheses are more precise, and clearly involve genetic factors. The rapid progress in this field raises the hope that more efficient treatments will appear in the near future.

Reflections on the cost consequences of the new gene technology for health policy

This article presents a preliminary and necessarily tentative and subjective assessment of the impact of new gene technology on health care costs. In the short term, diagnosis and treatment of genetic disease are likely to increase costs. Treatment with nongene therapy will continue to be far less expensive than gene therapy where it is available. Research developments to monitor as indicators of forthcoming cost reductions in genetic therapy are set forth. Some forms of genetic screening may soon reduce health care costs, and an example is provided. Genetically engineered pharmaceuticals are described and their impact on costs reviewed. Conditions under which they are likely to reduce health care costs are indicated.

Glutamate, beta-amyloid precursor proteins, and calcium mediated neurofibrillary degeneration

In this article we present evidence supporting the interaction between excitotoxicity, beta APP mismetabolism, metabolic compromise and intracellular calcium destabilization in the process of neurodegeneration associated with Alzheimer's disease (AD). AD is characterized by the presence of neurofibrillary tangles and amyloid-containing plaques in specific regions of the brain. There appear to be several processes which contribute to the neurodegeneration associated with AD. Although AD has been linked to genetic mutations on chromosomes 21, 19 and 14, there are sporadic forms of AD that have no known genetic mutation involved. Aging is the major risk factor for AD. During the course of normal aging several metabolic compromises may occur in the brain. Both decreased glucose transport and utilization, and increased glucocorticoid levels are known to occur with aging and may lead to decreased energy supplies, ATP depletion, failure of Ca2+ buffering systems, excess glutamate release and activation of glutamate receptors. In addition, a reduction in antioxidant enzymes and consequently an increase in free radicals has also been associated with aging. Each of the preceeding alterations would lead to an increase in neuronal [Ca2+]i. Elevated calcium could then activate calcium-dependent proteases which degrade particular cytoskeletal proteins, and lipases which generate free radicals resulting in membrane damage and possible cell death. In this article we provide evidence that amyloid beta-peptide (A beta), the substance which accumulates in AD plaques, exacerbates excitotoxic and metabolic compromises to neurons resulting in changes in the cytoskeleton which resemble those seen in the neurofibrillary tangles of AD. We also provide evidence that secreted forms of beta-amyloid precursor protein (beta APP) are neuroprotective against excitotoxic insults. Recent findings concerning the normal function of beta APP and the mechanism of A beta toxicity place beta APP at the center of changes leading to neuronal degeneration in AD.

Interaction between genetic and environmental risk factors for Alzheimer's disease: a reanalysis of case-control studies

To study the interaction among genetic and environmental risk factors, a reanalysis of case-control studies of Alzheimer's disease (AD) was conducted based on the original data of all studies carried out to January 1, 1990. Seven studies were included in the present analysis, comprising a total of 814 AD patients and 894 control subjects. When comparing those with a positive and negative family history of dementia, similar odds ratio were found for late maternal age [1.7; 95% confidence interval (0.6-4.8) vs. 2.0 (1.1-3.5)], head trauma [1.7 (0.7-4.2) vs. 1.9 (1.1-3.2)], and history of depression [2.0 (0.2-19.8) vs. 2.1 (0.8-1.7)]. This suggests a model in which these risk factors increase the risk for AD independent of family history of dementia. Among those with a positive family history of dementia, the odds ratios for family history of Down's syndrome [4.2 (0.9-20.0)] and of Parkinson's disease [3.3 (0.4-28.2)] tended to be higher than among those with a negative family history of dementia [2.6 (0.8-8.5) and 2.4 (0.8-7.0), respectively]. However, for both disorders the difference in odds ratio was not statistically significant. For history of cigarette smoking, there was no association to AD for those with no first degree relatives with dementia and an inverse relation with AD for those with a positive family history. Although in all analyses, family history of dementia remained significantly associated with AD in the absence of other factors, the odds ratio associated with family history of dementia tended to be lower for those with a positive smoking history, particularly for those with two or more affected relatives. These findings suggest that smoking may interact specifically with a genetically determined process.

Neurodegeneration, Alzheimer's disease, and beta-amyloid toxicity

In its majority, Alzheimer's disease is sporadic and with late onset. Therefore, age-related disturbances in cellular metabolism may come into focus with respect to the etiopathogenesis of this neurodegenerative disorder. As a possible primary abnormal event in sporadic Alzheimer's disease, a desensitization of the neuronal insulin receptor and the subsequent deficits in ATP and acetylcholine are discussed with its impact on protein processing in general and beta-amyloid formation in particular, and neurotoxicity of the latter.

apl-1, a Caenorhabditis elegans gene encoding a protein related to the human beta-amyloid protein precursor

The major component of senile plaques found in the brains of Alzheimer disease patients is the beta-amyloid peptide, which is derived from a larger amyloid precursor protein (APP). Recently, a number of APP and APP-related proteins have been identified in different organisms and constitute the family of APP proteins. We have isolated several cDNAs encoding an APP-related protein in the nematode Caenorhabditis elegans and have designated the corresponding gene as apl-1. The apl-1 transcripts undergo two forms of posttranscriptional modification: trans-splicing and alternative polyadenylylation. In vitro translation of an apl-1 cDNA results in a protein of approximately the expected size. Similar to the Drosophila, human, and mouse APP-related proteins, APL-1 does not appear to contain the beta-amyloid peptide. Because APP-related proteins seem to be conserved through evolution, the apl-1 gene from C. elegans should be important for determining the normal function of human APP.

Human dihydrolipoamide succinyltransferase: cDNA cloning and localization on chromosome 14q24.2-q24.3

We isolated cDNA for dihydrolipoamide succinyltransferase from a human fibroblast cDNA library in lambda gt11. The cDNA revealed that the human dihydrolipoamide succinyltransferase lacked a sequence motif of an E3 and/or E1 binding site. This suggests that the human dihydrolipoamide succinyltransferase possesses a unique structure consisting of two domains in contrast with the dihydrolipoamide acyltransferases of other alpha-keto acid dehydrogenase complexes. In addition, we found that the human dihydrolipoamide succinyltransferase gene is located on chromosome 14 at q24.2-q24.3 and that a sequence related to the dihydrolipoamide succinyltransferase gene is located on chromosome 1 at p31. Interestingly, the gene for the dihydrolipoamide acyltransferase of the branched chain alpha-keto acid dehydrogenase complex is also located on chromosome 1p31 (Zneimer et al. (1991) Genomics 10, 740-747).

Molecular genetics of Alzheimer's disease

At present it is not clear whether Alzheimer's disease is a single disease, a complex syndrome, or a heterogeneous ill-defined group of disorders. In the last few years significant progress has been made in identifying and describing its different manifestations, as well as the underlying biological mechanisms. Modern molecular biology techniques have provided new insights into possible etiological mechanisms. Linkage analysis and gene sequencing studies have produced evidence of a possible locus on chromosome 21 in a small group of families with early onset familial Alzheimer's disease (FAD). It was shown that another small group of early onset FAD families develops the disease as a result of mutations in the gene coding for the beta-amyloid precursor protein, and that in a larger subgroup of early onset families the disease appears to be caused by an unidentified gene on chromosome 14. Several other early onset FAD families are clearly not linked to any of these loci, suggesting that other abnormal genes, probably on different chromosomes, might be the cause of the disease in these families. Finally, it was recently shown that the epsilon 4 allele of apolipoprotein E (ApoE) gene, which has been mapped to chromosome 19, is associated with an increased risk of developing the disease in late onset FAD families and sporadic cases. These results not only evidence that Alzheimer's disease is a genetically heterogeneous disorder, but also delineate new approaches in the study of the etiological and pathogenetic mechanisms of Alzheimer's disease.

Molecular genetics in neurology

There has been remarkable progress in the identification of mutations in genes that cause inherited neurological disorders. Abnormalities in the genes for Huntington disease, neurofibromatosis types 1 and 2, one form of familial amyotrophic lateral sclerosis, fragile X syndrome, myotonic dystrophy, Kennedy syndrome, Menkes disease, and several forms of retinitis pigmentosa have been elucidated. Rare disorders of neuronal migration such as Kallmann syndrome, Miller-Dieker syndrome, and Norrie disease have been shown to be due to specific gene defects. Several muscle disorders characterized by abnormal membrane excitability have been defined as mutations of the muscle sodium or chloride channels. These advances provide opportunity for accurate molecular diagnosis of at-risk individuals and are the harbinger of new approaches to therapy of these diseases.

Alzheimer's disease: molecular genetics and transgenic animal models

Disease-causing mutations in the amyloid precursor protein (APP) gene have been found on chromosome 21 during the last 2 years in some early onset Alzheimer's disease (AD) families. Genetic evidence shows that other genes than the APP are also involved in the aetiology of AD. Linkage to a loci on chromosome 14 has been found in early onset disease. The identification of APP mutation has led to the realization that APP mismetabolism is a central event in the aetiology and pathogenesis of the disease. Experiments to test this in transgenic mice have so far met with little success. There are many possible explanations for the problems to generate transgenic mice. These include the possibilities that mice are incapable of developing AD for reasons dependent on their APP sequence; and that appropriate regulation of APP gene is required for pathology to develop. Current attempts that seem promising to model the disease pathology are the use of homologous recombination to insert the pathogenic mutation and transfection of YACs into transgenic animals.

Clinical studies in Alzheimer patients with positron emission tomography

Brain imaging techniques will in the future play an important role in the assessment of patients with neurogenerative disorders such as Alzheimer's disease (AD). An early diagnosis of AD is today hampered by lack of reliable diagnostic markers. Positron emission tomography (PET) permits the quantification and three-dimensional imaging of physiological variables. This provides the clinician with a non-invasive imaging technique which allows in vivo quantification of physiological processes in AD underlying dysfunction of cognition. PET studies regarding changes in cerebral blood flow and metabolism are rather consistent at least in moderate/advanced cases of AD. How early in the progress of the disease deficits in these parameters can be observed is still an open question. Longitudinal studies will here be important and especially in individuals with a family history of AD. Since deficits in cholinergic neurotransmission have been measured in autopsy AD brains attempts have also been made to visualized cholinergic activity in vivo. Nicotinic and muscarinic receptors have been visualized in normal and AD brains. A reduced uptake and binding of [11C]nicotine in the temporal and frontal cortices have been measured in AD patients by PET. Few treatment studies in AD have been evaluated by PET. Long-term treatment with the cholinesterase inhibitor tacrine increase the uptake of [11C]nicotine. Significant reduction in uptake between the two enantiomers (S)(-) and (R)(+)-[11C]nicotine has been observed compatible with a restoration of nicotinic receptors. Tacrine also significantly increased the glucose metabolism. PET studies indicate that long-term tacrine treatment in AD patients with mild dementia improves functional activities in brain. When an AD patient with moderate dementia was treated with nerve growth factor (NGF) PET studies revealed increase in cortical blood flow and nicotinic receptors. PET studies will in the future play an important role in the evaluation of new therapeutic drug strategies in AD.

Absence of linkage disequilibrium at amyloid precursor protein gene locus in Japanese familial Alzheimer's disease with 717Val-->Ile mutation

To date, eleven independent FAD pedigrees with the 717Val-->Ile mutation have been identified. Interestingly, five pedigrees were of Japanese origin and four were of British origin. The apparent ethnic prediction of this mutation raises the possibility that there is a founder effect in these two island nations. We did not observe any significant linkage disequilibrium in any locus of APP and GT12 loci in the five Japanese FAD pedigrees with the 717Val-->Ile mutation. A founder effect would probably not be present in Japanese FAD pedgrees with the 717Val-->Ile mutation.

The differential diagnosis of adult onset metachromatic leukodystrophy and early onset familial Alzheimer disease in an Alzheimer clinic population

Clinical differentiation between forms of progressive dementia can prove difficult, particularly when relatively rare forms of dementia are involved. Factors such as family history of dementia, age at onset, presenting features such as personality change, cognitive deficits, psychiatric symptoms, and clinical course (progressive deterioration; retention of skills over time) may prove useful for directing investigations to identify underlying pathology and genetic implications. This is illustrated by two patient reports. Each patient had the onset of memory/behavioral problems at approximately age 40 years, was initially given a psychiatric, non-dementing diagnosis, and had a positive family history for early onset behavioral and memory problems. After longitudinal assessment, the diagnosis of Alzheimer disease was confirmed at autopsy in one patient and a diagnosis of familial, adult-onset metachromatic leukodystrophy in the other.

Age of onset in familial early onset Alzheimer's disease correlates with genetic aetiology

Age of onset is the most robust clinical feature demarcating aetiologic subtypes of familial Alzheimer's disease. It has previously been noted that early onset disease (arbitrarily below the age of 65 years) conforms to an autosomal dominant pattern of transmission. Late onset disease is generally thought to have a more complex aetiology. We present data here suggesting that early onset disease can be subdivided by genetic aetiology with which age of onset correlates. In general, those pedigrees showing linkage to the chromosome 14 locus have a mean age of onset in the forties whereas those pedigrees with an APP mutation have an age of onset in the fifties.

Biochemistry of Alzheimer's disease amyloid plaques

One of the principal identifying features of Alzheimer's disease (AD) is the extracellular deposition of fibrous protein aggregates in the form of amyloid plaques. The major component of these deposits is the amyloid beta (A beta) protein that is a proteolytic fragment of the integral membrane amyloid precursor protein (APP). Understanding the pathways responsible for A beta formation and the mechanism by which it accumulates within the brain could provide key answers to AD pathogenesis. This review will explore the biochemistry of A beta and its precursor, the possible causal relationship between amyloid and AD-associated neuronal death, the role of additional cellular elements in amyloid formation, and the potential application of these components in clinical diagnosis.

Apolipoprotein E in sporadic Alzheimer's disease: allelic variation and receptor interactions

An increased prevalence of apolipoprotein E (ApoE) epsilon 4 allele exists in late onset familial Alzheimer's disease. We found, in sporadic Alzheimer's disease, that 62% of patients possessed an ApoE-epsilon 4 allele, compared with 20% of controls. ApoE-epsilon 4/4 patients had more senile plaques (SPs) than epsilon 3/3 patients. ApoE immunoreactivity of SPs was equivalent in both groups. Two receptors bind ApoE complexes, the low density lipoprotein (LDL) receptor and the LDL receptor-related protein (LRP). In normal brain, anti-LRP antibodies strongly stained neurons and lightly stained astrocytes; anti-LDL receptor antibodies stained only the neuropil and astrocytes. In Alzheimer's disease, SPs and reactive astrocytes were also strongly LRP immunoreactive. Colocalization of ApoE and LRP to SPs implies that these molecules may be involved in metabolism of components of SPs.

Physiological production of the beta-amyloid protein and the mechanism of Alzheimer's disease

The progressive deposition of the beta-amyloid peptide in the brain and its microvasculature is an invariant feature of Alzheimer's disease that appears to precede the onset of dementia by many years. It had been assumed that the proteolytic release of beta-amyloid peptide from the transmembrane region of its large precursor protein was an aberrant event, requiring prior membrane injury. However, it has recently been shown that beta-amyloid peptide is continuously secreted from healthy neural and non-neural cells in culture and circulates in human CSF and blood. The finding that beta-amyloid peptide is a normal, soluble product of cellular metabolism has led to many dynamic studies of its formation and clearance in health and in genetic forms of Alzheimer's disease, and should facilitate the design of amyloid-inhibiting therapeutics.

Heterogeneity in Alzheimer's disease

The genetic data implicating mutations framing the beta-amyloid segment of the amyloid precursor protein as causes of Alzheimer's disease are reviewed and integrated with information on the normal processing of the amyloid precursor protein. The data indicating that there is a second and quantitatively major locus for early-onset Alzheimer's disease on the long arm of chromosome 14 are reviewed. The prediction that this second genetic locus will produce a protein intimately involved in the metabolism of the amyloid precursor protein is reiterated, together with the prediction that all causes of Alzheimer's disease will directly involve this process.

Sporadic dementia of Alzheimer type: role of amyloid in etiology is challenged

Alzheimer's disease is a heterogeneous neurodegenerative disorder. Whereas only a minority is due to genetic abnormalities and mostly with early onset, the majority of all Alzheimer cases is sporadic and with late onset. Therefore, in the latter, age-related disturbances in cellular metabolism may come into focus with respect to the etiopathogenesis rather than the primary formation of amyloid. In this "Editor's note for debate", the role of amyloid as a causative factor of sporadic Alzheimer's disease is challenged. Instead, as a possible primary abnormal event in sporadic Alzheimer's disease, the perturbations in neuronal glucose metabolism and the subsequent ATP deficit with its impacts on the secondary amyloid formation are discussed to open a new field of research and another aspect for debate.

Genetic and molecular advances in Alzheimer's disease

The abnormal deposition of amyloid beta protein (A beta) in the brain is the major neuropathological characteristic of Alzheimer's disease (AD). The disease in some early-onset familial cases develops as a result of mutations in the gene coding for the beta-amyloid precursor protein (beta APP) and in the majority of the rest appears to be caused by an unidentified gene on chromosome 14. Only one of the beta APP gene mutations has been associated with aberrant beta APP processing, resulting in an excess production of A beta in vitro, a result suggesting that there might be excessive A beta cleavage from beta APP in AD in vivo. By contrast with the beta APP mutants, no particular allele of the apolipoprotein E (APOE) gene predicts the disease completely but one allele is associated with the disease suggesting APOE is a risk locus for AD. This discovery has been linked to increased deposition of A beta in those cases carrying the risk allele. However, the genetic evidence is currently not sufficient to indicate whether beta APP mismetabolism, direct or indirect A beta neurotoxicity or dysfunction of beta APP (or its derivatives) are central to the AD process.

Searching for human epilepsy genes: a progress report

Application of new genetic techniques has brought remarkable discoveries in the study of genetic diseases. The potential benefits from applying such technology to idiopathic epilepsies include improved understanding of cellular mechanisms and potential new methods of prevention and treatment. The complex problems involved in studying the hereditary epilepsies include: defining of specific phenotypes; detecting genetic and non-genetic heterogeneity; and specifying the appropriate mode of inheritance and penetrance. The gene loci for three primary epilepsies have been localized to specific chromosomal regions, and serve to demonstrate the process used in generalized linkage studies of hereditary epilepsy syndromes. Benign familial neonatal convulsions (BFNC) and Unverricht-Lundborg progressive myoclonus epilepsy are rare single-gene disorders that are sufficiently localized to chromosomal regions that positional cloning studies are likely to succeed. Juvenile myoclonic epilepsy (JME), a common hereditary syndrome with an uncertain mode of inheritance, has been reported to be linked to chromosome 6p. JME presents a challenge for generalized linkage methodology that may be overcome by attending to potential problems reviewed here. The candidate-gene method, combined with studies using animal models, holds promise for understanding these as well as other hereditary epilepsies.

Heat-shocked neuronal PC12 cells reveal Alzheimer's disease--associated alterations in amyloid precursor protein and tau

The Alzheimer's disease (AD) brain contains many abnormal protein modifications. These include the abnormal processing of amyloid precursor protein (APP) to form the amyloidogenic beta/A4 peptide and the abnormal phosphorylation of tau to form A68, the major constituent of the neurofibrillary tangle. In addition, many of the biochemical alterations found in the AD brain are also found in heat-shocked or stressed cells. We used heat-shocked neuronal PC12 cells to investigate the effects of stress on APP and tau. We found that by simply exposing neuronal PC12 cells to an elevated temperature (45 degrees C) for 30 minutes, they exhibited several features characteristic of the heat shock response. These included a 45% reduction in total protein synthesis, the induction of heat shock protein (hsp) 72, and increased phosphorylation of the protein synthesis initiation factor eIF-2 alpha. The heat-shocked cells also exhibited alterations in the metabolism and phosphorylation of APP. Under heat shock conditions, we found two additional APP-like polypeptides not present in controls and a significant decrease in the phosphorylation state of APP. We also found that an A68-like protein is formed in neuronal PC12 cells when subjected to elevated temperature. This A68-like protein was formed with heat shock even in the absence of protein synthesis, suggesting that its production occurred post-translationally. The tau/A68 polypeptides were identified as phosphoproteins, and the phosphorylation of tau to form A68 was reversed with recovery of the cells from heat shock. Immunoprecipitation of lysates from heat shocked cells with antibodies to hsp72/73 resulted in co-precipitation of tau, but not A68 with hsp72 indicating a stable complex formation between these two proteins. These results suggest that heat shock proteins may play either a protective or promoting role in the formation of A68 and/or the amyloidogenic C-terminal fragment of APP.

Search for the genes responsible for familial Alzheimer's disease

Inherited or Familial Alzheimer's Disease (FAD) has clearly been shown to be a genetically heterogeneous disorder. Mutations in the gene on chromosome 21 encoding the beta-amyloid protein precursor (APP) have been shown to be linked to 2-3% of FAD kindreds examined around the world. A late onset FAD locus has been mapped to a region of chromosome 19 in which a recently isolated APP-like gene, APLP1 has also been localized, making this gene a strong candidate to harbor a late-onset FAD defect. More recently, a major FAD locus has been mapped to the long arm of chromosome 14. The chromosome 14 locus appears to be mainly linked to the gene defect in early onset FAD pedigrees. Besides the FAD loci on chromosome 21, 19, and 14, at least two other loci must exist since the gene defect in some early- and late-onset FAD pedigrees do not appear to segregate with markers from any of these autosomes. As different gene defects responsible for various forms of FAD are discovered, perhaps, a common basis for the etiology of this devastating disorder can be discerned.

Regulation and expression of the Alzheimer's beta/A4 amyloid protein precursor in health, disease, and Down's syndrome

A four- to fivefold overexpression of the gene for the Alzheimer beta/A4 amyloid precursor protein (APP) in individuals with Down's Syndrome (DS) appears to be responsible for the fifty year earlier onset of Alzheimer's disease (AD) pathology in DS compared to the normal population. It is therefore likely that a deregulated overexpression of the APP gene is a risk factor for the beta/A4 amyloid formation. To test this hypothesis and to get a better understanding of how APP expression is regulated, we studied the 5' control region of the human APP gene, alternative splicing of the 19 APP exons, and APP biogenesis, metabolism and function. The analysis of the APP promoter revealed its similarity with those of housekeeping genes by the presence of a GC-rich region around the transcription start site and the lack of a TATA box. Gene transfer experiments showed this GC-rich region to contain overlapping binding sites for different transcription factors whose binding is mutually excluded. An imbalance between these factors may cause APP overexpression and predispose to AD pathology. Another putative risk factor for AD is regulation of splicing of exon 7 in APP mRNA's which changes in brain during aging. This is relevant for APP processing since exon 7 codes for a Kunitz protease inhibitory domain. Investigation of further splicing adjacent to the beta/A4 exons 16 and 17 which might also interfere with APP processing led to the identification of the leukocyte-derived (L-APP) splice forms which lack exon 15. In brain this splicing occurs in activated astrocytes and microglia. The localization of APP at synaptic sites in brain suggests that APP regulation and expression are critical determinants of a potential and early impairment of central synapses. This may be the case during pathological evolution of AD and DS when beta/A4 derived from synaptic APP is converted to beta/A4 amyloid by radical generation.

Apolipoprotein E polymorphism and Alzheimer's disease

Apolipoprotein E (apoE) is associated with Alzheimer's neurofibrillary tangles and beta-amyloid protein in senile plaques. It also appears to play an important part in the redistribution of lipids that follows deafferentation and neurodegeneration in the brain. The gene for apoE is on chromosome 19, within the genomic region previously associated with late-onset familial Alzheimer's disease (AD). We have studied apoE phenotype expression and the corresponding allele frequencies (epsilon 2, epsilon 3, epsilon 4) in 91 patients with sporadic AD and 74 controls. There was a significant association between epsilon 4 and sporadic AD (epsilon 4 frequency 0.380 in AD and 0.122 in controls, p < 0.01). Analysis of epsilon 4 in whom AD develops this tended to happen earlier in life than in those with epsilon 3 or epsilon 2. The epsilon 4/AD association was more pronounced in women. Octogenarians with AD had an epsilon 4 allele frequency that was 3 times higher than one reported, in a different study, in healthy octogenarians. ApoE may be an important susceptibility factor in the aetiopathology of sporadic AD.

The c-fos gene and early-onset familial Alzheimer's disease

A gene for early-onset familial Alzheimer's disease (FAD) is located on chromosome 14q24.3. The c-fos gene (FOS) is also located in the same band of this chromosome and is thus a candidate for the FAD locus. A yeast artificial chromosome (YAC) clone was identified which contains FOS. This YAC also contains the short-tandem repeat polymorphic (STRP) locus D14S76, placing FOS in the FAD region between D14S53 and D14S43. No recombinants were observed between D14S76 and FAD, and a maximum positive LOD score of 7.20 at a recombination fraction of 0.001 was observed for linkage of this marker to FAD. DNA sequence analysis was used to examine FOS in two affected subjects from an FAD family in which the chromosome 14 FAD locus is clearly responsible for the disease. The coding regions and parts of the 5' and 3' untranslated sequences of FOS were sequenced; no FAD-related mutations were observed. This work suggests that the FOS gene is not the chromosome 14 FAD locus although we cannot exclude the possibility that a mutation in an as yet unknown regulatory region is responsible for the disease. A new polymorphism was detected in the third intron of the gene.

Potassium channel dysfunction in fibroblasts identifies patients with Alzheimer disease

Since memory loss is characteristic of Alzheimer disease (AD), and since K+ channels change during acquisition of memory in both molluscs and mammals, we investigated K+ channel function as a possible site of AD pathology and, therefore, as a possible diagnostic index as well. A 113-pS tetraethylammonium (TEA)-sensitive K+ channel was consistently absent from AD fibroblasts, while it was often present in young and aged control fibroblasts. A second (166-pS) K+ channel was present in all three groups. Elevated external potassium raised intracellular Ca2+ in all cases. TEA depolarized and caused intracellular Ca2+ elevation in young and aged control fibroblasts but not AD fibroblasts. The invariable absence of a 113-pS TEA-sensitive K+ channel and TEA-induced Ca2+ signal indicate K+ channel dysfunction in AD fibroblasts. These results suggest the possibility of a laboratory method that would diagnostically distinguish AD patients, with or without a family history of AD, from normal age-matched controls and also from patients with non-AD neurological and psychiatric disorders.

Isolation and characterization of APLP2 encoding a homologue of the Alzheimer's associated amyloid beta protein precursor

Familial Alzheimer's disease (FAD) is a genetically heterogeneous disorder that includes a rare early-onset form linked to mutations in the amyloid b protein precursor (APP) gene. Clues to the function of APP derive from the recent finding that it is a member of a highly conserved protein family that includes the mammalian amyloid precursor-like protein (APLP1) gene which maps to the same general region of human chromosome 19 linked to late-onset FAD. Here we report the isolation of the human APLP2 gene. We show that APLP2 is a close relative of APP and exhibits a very similar pattern of expression in the brain and throughout the body. Like APP, APLP2 contains a cytoplasmic domain predicted to couple with the GTP-binding protein G(o) indicating that it may be an additional cell surface activator of this G protein.

Conjugal Alzheimer's disease: is there an increased risk in offspring?

Thirty-one couples in which both spouses had the clinical diagnosis of Alzheimer's disease (AD) (confirmed by autopsy in 12) were ascertained. The mean age of onset of dementia was 75.1 +/- 7.4 years. These couples had 87 children, 63 still living. Seventeen (19.5%) of the children developed dementia, with a mean age of onset of 68.9 +/- 8.3 years. Thirty of the children of the conjugal AD couples survived to age 65 or longer and 14 (47%) of them developed dementia. This prevalence of dementia in the children of affected couples is much greater than that in the children of two control groups consisting of 234 couples in which one spouse had AD and 192 couples in which neither spouse was demented. Twenty-one of the conjugal AD couples had a family history of AD but the prevalence of dementia in their children was not greater than that in the children of conjugal AD couples without a family history of AD. These results represent additional evidence of an important genetic component in late-onset AD and provide empirical risk data for the children of conjugal AD couples.

Gene dose of apolipoprotein E type 4 allele and the risk of Alzheimer's disease in late onset families

The apolipoprotein E type 4 allele (APOE-epsilon 4) is genetically associated with the common late onset familial and sporadic forms of Alzheimer's disease (AD). Risk for AD increased from 20% to 90% and mean age at onset decreased from 84 to 68 years with increasing number of APOE-epsilon 4 alleles in 42 families with late onset AD. Thus APOE-epsilon 4 gene dose is a major risk factor for late onset AD and, in these families, homozygosity for APOE-epsilon 4 was virtually sufficient to cause AD by age 80.

Action of the diabetogenic drug streptozotocin on glycolytic and glycogenolytic metabolism in adult rat brain cortex and hippocampus

In sporadic Alzheimer's disease (AD), a number of metabolic alterations to the brain have been observed soon after the onset of the initial clinical symptoms. In particular, impairments of glucose utilization and related metabolic pathways are prominent and well-established findings in incipient AD, resembling metabolic abnormalities such as have been found in noninsulin-dependent diabetes mellitus. To mimic these abnormalities, we administered an intracerebroventricular (icv) injection of streptozotocin (STZ) to rats and studied the effects of glucose and glycogen metabolism in the cerebral cortex and hippocampus compared with controls. The enzymatic activities studied dropped significantly by 10-30% in brain cortex (cort.) and hippocampus (hc) 3 and 6 weeks after icv STZ injection: hexokinase (15% 3 weeks cort.; 14% 6 weeks cort.; 12% 3 weeks hc; 28% 6 weeks hc), phosphofructokinase (15%; 15%; 24%; 15%), glyceraldehyde-3-phosphate dehydrogenase (10%; 12%; 30%; 19%), pyruvate kinase (22%; 13%; 22%; 28%), glucose-6-phosphatase (10%; 23%; 14%; 19%) and phosphorylase a (22%; 11%; 30%; 15%). The content of glycogen was significantly higher in STZ-treated rats than in control animals (7% 3 weeks and 15% 6 weeks in cortex). In contrast to the reduced enzymatic activities, we observed no changes in the concentrations of the glycolytic intermediates glucose, glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-diphosphate, pyruvate, lactate and glucose-1-phosphate. These data clearly indicate reduced glycolytic enzyme activity after icv administration of STZ and suggest gluconeogenesis consequent on abnormalities in glucose breakdown. This model may thus be assumed to be a useful tool to investigate pathogenetic factors involved in sporadic dementia of Alzheimer type.

Genetic transmission of Alzheimer's disease among families in a Dutch population based study

We evaluated age at onset and transmission patterns of Alzheimer's disease (AD) in families of 198 patients who had onset of symptoms before the age of 65 years and were diagnosed before the age of 70 years. Patients were ascertained in a population based study in The Netherlands. The results suggest that the risk of AD by the age of 90 in first degree relatives is 39% (95% confidence interval 27 to 51). By the age of 90, this risk is 2.8 (95% confidence interval 1.5-5.2) times greater than the corresponding risk of 14% among relatives of age and sex matched control subjects. Segregation analysis indicated that patterns of familial clustering are best explained by transmission of a major autosomal dominant gene with reduced penetrance and a multifactorial component. However, the single major locus model could be rejected in favour of the mixed model only when a cohort effect for heritability was allowed for. The frequency of the AD susceptibility allele was estimated to be 0.48% in the single major locus model and 0.31% in the mixed model. Although our study confirms that a dominant major gene is implicated in early onset AD, the results suggest that other genetic or perhaps non-genetic factors may account for the disease in a considerable number of patients.

Alzheimer disease and the prion disorders amyloid beta-protein and prion protein amyloidoses

Alzheimer disease and the prion disorders/spongiform encephalopathies share many common features. These chronic, progressive, sometimes familial diseases of the central nervous system are characterized by the presence of different types of amyloid deposits in the brain. This review provides a perspective on these two types of neurodegenerative disorders.

The gene for Machado-Joseph disease maps to human chromosome 14q

Machado-Joseph disease (MJD) is an autosomal dominant, multisystem neurodegenerative disorder involving predominantly cerebellar, pyramidal, extrapyramidal, motor neuron and oculomotor systems. Although it was first reported in families of Portuguese-Azorean descent, MJD has also been described in non-Azorean families from various countries, being one of the most common hereditary spinocerebellar degenerations. With the use of highly polymorphic microsatellite DNA polymorphisms, we have assigned the gene for MJD to the long arm of chromosome 14 (14q24.3-q32) by genetic linkage to microsatellite loci D14S55 and D14S48 (multipoint lod score Zmax = 9.719).

Alzheimer's disease and chromosome 14. Different gene, same process?

Over the past three years, progress in the molecular genetics of familial Alzheimer's disease has been fast and fundamental. The seminal finding that some cases are due to a mutation in the β-amyloid precursor protein (APP) gene has been followed by the discovery of a major additional locus for the disease on chromosome 14. The combined data suggest that the genetic sites accounting for most early-onset familial Alzheimer's disease cases have now been located. In addition, research is revealing the mechanisms by which the genes exert their pathogenicity. This promises to provide the explanatory link between the genes and the clinicopathological syndrome. The ultimate goal, an understanding in similar terms of the much commoner senile, sporadic form of Alzheimer's disease, is now a realistic target.