Beta amyloid gene duplication in Alzheimer's disease and karyotypically normal Down syndrome

The relationship between enlargement of the temporal horns of the lateral ventricles and dementia in aging patients with Down syndrome

Head CT studies of patients with Alzheimer's disease (AD) show global atrophic changes. Tissue loss is especially prominent in the temporal lobes, with widening of the temporal horns of the lateral ventricles and, usually, widening of the temporal sulci. Some recent studies have found a familial form of AD to be mapped to chromosome 21. Down syndrome (DS) results from the inheritance of three chromosomes 21, and it has been shown that after the age of 35 the brains of patients with DS commonly show neuropathological changes similar to those in patients with AD. CT studies of 25 patients with DS (ages 29-64 years) were examined for tissue loss in the temporal regions, and this was compared to the findings commonly seen in patients with AD. The widths of CSF spaces varied considerably in patients with DS, but after the age of 50 most of them showed significant widening of the temporal horns. In some patients the horns were large enough to suggest obstructive hydrocephalus. Because of a new trend toward deinstitutionalization of patients with DS, radiologists will be seeing more studies on these patients and should familiarize themselves with the unique ways in which they manifest the aging process.

Amyloidosis of the nervous system

Various types of amyloid fibril deposits occur in the nervous system with unique clinical characteristics and pathogeneses. Genetic mutations cause the familial amyloidotic polyneuropathies and acquired polyneuropathies occurring particularly in patients suffering from hypernephromas and myelomas also result from the production of abnormal proteins. Amyloid fibril deposits in cerebral plaques and vessels consisting of beta-protein are seen in acquired and familial Alzheimer's disease and in Down's syndrome individuals over 40 years of age. This amyloid fibril deposition could result from a mutational, transcriptional or post-translational alteration in these pathologic processes with most evidence supporting the latter. Other diseases including hereditary cerebral hemorrhage of the Dutch type and Batten's disease involve beta-amyloid deposition. The features of the familial and transmissible forms of the spongiform encephalopathies are associated with the prion protein which comprises the amyloid fibril deposits in these conditions. This wide variety of nervous system disorders having amyloid deposits as their primary or subsidiary characteristic make studies of these conditions intriguing models for research workers in clinical, pathologic and molecular biologic fields.

The amyloid proteins of Alzheimer's disease as potential targets for drug therapy

Two amyloid proteins accumulate in Alzheimer's disease. These proteins, beta amyloid protein and paired helical filament protein, are present in the hallmark lesions of Alzheimer's disease, neuritic plaques and neurofibrillary tangles. Although the amino acid sequences of these two proteins are likely to be different, they nevertheless share certain physical characteristics which define each as belonging to a common class of proteins, amyloid proteins. Since these proteins are probably important in the pathology of Alzheimer's disease, drugs that prevent their accumulation should have therapeutic utility. Based on the amyloidoses associated with other diseases, three mechanisms for amyloid formation have emerged. These mechanisms form a framework for studying Alzheimer amyloids and designing interventions. One mechanism involves posttranslational events which render a normal protein amyloidogenic. Proteolysis, phosphorylation, glycosylation, and transglutamination may be relevant posttranslational events in Alzheimer's disease. If more conclusive evidence can be generated suggesting that these events are involved in the abnormal formation of amyloid in Alzheimer's disease, then these events will become viable targets for drug therapy. Another mechanism for amyloid formation results from expression of an abnormal gene which, in the case of familial Alzheimer's disease, may be an important etiological component. A third mechanism involves the accumulation of a normal protein to a threshold concentration that spontaneously forms amyloid. An effective therapeutic approach for these last two mechanisms could likely include pharmacological manipulation of gene expression.

Critical role of the D21S55 region on chromosome 21 in the pathogenesis of Down syndrome

The duplication of a specific region of chromosome 21 could be responsible for the main features of Down syndrome. To define and localize this region, we analyzed at the molecular level the DNA of two patients with partial duplication of chromosome 21. These patients belong to two groups of Down syndrome patients characterized by different partial trisomies 21: (i) duplication of the long arm, proximal to 21q22.2, and (ii) duplication of the end of the chromosome, distal to 21q22.2 We assessed the copy number of five chromosome 21 sequences (SOD1, D21S17, D21S55, ETS2, and D21S15) and found that D21S55 was duplicated in both cases. By means of pulsed-field gel analysis and with the knowledge of regional mapping of the probes D21S17, D21S55 and ETS2, we estimated the size of the common duplicated region to be between 400 and 3000 kilobases. This region, localized on the proximal part of 21q22.3, is suspected to contain genes the overexpression of which is crucial in the pathogenesis of Down syndrome.

Disturbance of cerebral function by aluminium in haemodialysis patients without overt aluminium toxicity

The psychomotor function of 27 long-term haemodialysis patients with apparently normal cerebral function, who had only mildly raised serum aluminium (mean 59 [SEM 9] micrograms/l), was measured by means of a computerised version of the symbol digit coding test. Compared with those of control subjects matched for age and the patients' estimated premorbid IQ, the patients' response times were significantly longer (2.51 [0.10] vs 1.88 [0.05] s). Abnormalities were also detected in five other computerised tests of psychomotor function. The mean activity of erythrocyte dihydropteridine reductase (DHPR), which is inhibited by aluminium, rose during 3 months' desferrioxamine treatment in most of the 15 patients so treated. Although there was no relation between baseline psychomotor function and either indices of cumulative aluminium exposure or erythrocyte DHPR activity, changes in DHPR induced by desferrioxamine correlated with changes in psychomotor performance (r = 0.62). The flash-stimulated visual evoked potential (measured in 10 patients) was delayed (133.4 [2.4] ms), although the pattern-stimulated visual evoked potential remained normal (101.8 [3.2] ms). The difference between the visual evoked potentials stimulated by flash and pattern was significantly greater in the patients than in the controls (31.6 [4.3] vs 19.4 [2.4] ms) and was significantly related to the symbol digit coding response times and to the oral aluminium intake. The results suggest that much more rigorous exclusion of aluminium from the dialysate and diet of dialysis patients is necessary.

Decreased DNA repair in familial Alzheimer's disease

Alterations in the capacity of a cell to repair DNA lesions play an important role in a number of human diseases. We and others have demonstrated defective DNA repair of alkylation damage in cells from patients with Alzheimer's disease. It has been hypothesized that this defect is related to the cause of Alzheimer's disease and results in the accumulation of lesions in the central nervous system neurons. One prediction of this hypothesis is that in dominantly inherited Alzheimer's disease, the repair defect will be present in half of the offspring of affected patients long before they develop symptoms of the disease. In order to test the hypothesis that decreased DNA repair is responsible for familial Alzheimer's disease and their at-risk offspring we have studied DNA repair in these individuals after exposure of lymphoblasts to alkylating agents. Our results indicate that cell lines from affected patients repair significantly less damage in 3 h than cell lines from healthy controls. A small number of at-risk individuals were also studied and some of these had lower levels of repair, although more cell lines from individuals in this group must be studied. These findings provide further support for defective DNA repair playing a role in the pathogenesis of Alzheimer's disease.

Amyloid A4 protein and its precursor in Down's syndrome and Alzheimer's disease

In patients with Alzheimer's disease, amyloid fibrils that are aggregates of A4 protein subunits are deposited in the brain. A similar process occurs at an earlier age in persons with Down's syndrome. To investigate the deposition of amyloid in these diseases, we used a radioimmunoassay to measure levels of the amyloid precursor (PreA4) in the serum of 17 patients with Down's syndrome, 15 patients with Alzheimer's disease, and 33 normal elderly controls. The mean (+/- SD) concentration of serum PreA4 was increased 1.5-fold in patients with Down's syndrome (2.49 +/- 1.13 nmol per liter) as compared with that in controls (1.68 +/- 0.49 nmol per liter; P less than 0.007); the levels in patients with Alzheimer's disease were similar to those in controls (1.83 +/- 0.78; P less than 0.98). We also found that the concentration of PreA4 in the brain tissue of two adults with Down's syndrome (100 and 190 pmol per gram) was higher than that in the brain tissue of either 26 patients with Alzheimer's disease (64.4 +/- 17.3 pmol per gram) or 17 elderly controls with neurologic disease (68.5 +/- 26.3 pmol per gram). Immunocytochemical studies of brain tissue from 26 patients with Down's syndrome showed that the deposition of A4 protein amyloid began in these patients approximately 50 years earlier than it began in 127 normal aging subjects studied previously, although the rate of deposition was the same. We conclude that, since the gene for PreA4 is on the long arm of chromosome 21, which is present in triplicate in Down's syndrome, overexpression of this gene may lead to increased levels of PreA4 and amyloid deposition in Down's syndrome. However, since increased levels of PreA4 are not present in Alzheimer's disease, additional factors must account for the amyloid deposition in that disorder.

Distinguishing Alzheimer's disease from other dementias. Questionnaire responses of close relatives and autopsy results

Epidemiologic study of Alzheimer's disease by family history requires that Alzheimer's be distinguished from other dementias. Identification of demented family members is usually based on recall by relatives. This study examines the validity of the classification of Alzheimer's disease and other dementias based on relatives' reports. Close relatives of autopsy-confirmed dementia cases were asked to complete a questionnaire describing the patient's symptoms. These informants were familiar with the patient's disease and involved in his/her care prior to death. The questionnaire included the DSM-III criteria for Primary Degenerative Dementia and the Hachinski Ischemic Scale. A diagnosis derived from the close relatives' responses was compared to the neuropathologic diagnosis for thirty-six cases: 20 Alzheimer's disease, 9 mixed Alzheimer's disease, and 7 non-Alzheimer's disease dementias. The diagnosis of Primary Degenerative Dementia derived from questionnaire responses had a sensitivity of 0.93 and specificity of 0.43 for pathologic Alzheimer's disease. Few vascular dementias were included in the series, thereby precluding the study of so-called multi-infarct dementia. Hachinski scores based on relatives' responses classified 40% of pathologically pure Alzheimer's disease cases as multi-infarct dementia (HIS greater than 7). Thus, using these elevated Hachinski scores to rule out Alzheimer's disease would cause substantial misclassification. Diagnosis based on questionnaire Primary Degenerative Dementia criteria was quite sensitive but relatively nonspecific. When attempting to obtain a complete family history or pedigree that describes the occurrence of Alzheimer's disease and other dementias in all family members, the questionnaire approach should be supplemented with additional information from medical records, physicians, and other relatives.

Altered expression of genes for amyloid and cytoskeletal proteins in Alzheimer cortex

Recent studies have indicated a normal gene dose for the amyloid precursor protein (APP) in Alzheimer's disease (AD). These findings leave open the possibility that elevated levels of messenger RNA (mRNA) for this protein may contribute to the pathogenesis of AD. Using Northern analysis, we compared the levels of mRNA for the APP and 3 cytoskeletal proteins in parietal cortex of 6 brains having marked AD-type degeneration with the levels of these mRNAs in 6 control samples. The cytoskeletal mRNAs studied were those for the human neurofilament 68-kDa subunit (HNFL), for alpha-tubulin, and for glial fibrillary acidic protein (GFAP). A ribonuclease (RNase) protection assay was also used to compare AD and control HNFL mRNA levels. The mRNAs for APP, HNFL, and alpha-tubulin were diminished in AD cortex. The decrement for APP mRNA was less than that for HNFL or alpha-tubulin. The message for GFAP in AD cortex showed no loss. The findings support a general deficit in neuronal mRNAs, including that for APP. They do not exclude the possibility of elevated levels of the message for the APP in small neuronal subsets, in subcortical neurons projecting to cortex, or as a generalized phenomenon in earlier stages of the disease.

Molecular genetic approaches to Alzheimer's disease

Alzheimer's disease (AD) has emerged in the past decade as a major public health problem. Epidemiological and neuropathological studies have revealed AD to be a very frequent disease associated with aging. Already the fourth leading cause of death in the USA and consuming a major component of health care costs, AD will take on even greater importance with the continuous growth of the elderly population. A concerted effort has been made in recent years to attack AD using an arsenal of powerful molecular biological techniques, concentrating on two areas: the characterization of proteins implicated in the pathogenesis of AD and of the genes that encode them; and the use of genetic linkage to approach the primary defect in a familial form of AD (FAD). This review attempts to summarize and interpret the recent molecular, genetic and biochemical findings concerning the pathogenesis of 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.

Genetics, Alzheimer's disease and senile dementia

Genetic factors in the aetiology of Alzheimer's disease (AD), are now being intensively investigated. The homogeneity of AD is under investigation. There are a few large kindreds with early onset of AD in whom transmission appears to be typically autosomal dominant, and 65% or more of the remaining cases at any age may have genetic aetiology. Both multifactorial and autosomal dominant inheritance with age-dependent expression have been proposed, but the late onset and death of unaffected relatives from competing causes make it difficult to choose between them. Lifetime risk gives the best estimate of incidence in family studies, but clinical and pathological criteria are not clear enough for confident diagnosis of AD in late old age. A role for external factors is indicated by twin studies, and the role of aluminium is currently under investigation. Molecular genetics promises to resolve many questions. The clinicians' role will be to provide well documented families for interdisciplinary research and to help in clarifying diagnosis in late old age.

The neurobiology of Alzheimer's disease

The defining histological characteristics of Alzheimer's disease (AD) are neurofibrillary tangles and neuritic plaques, although neither is pathognomonic for this disorder. The distribution of AD histopathology suggests selective neuronal vulnerability, with specific cell populations affected within discrete regions of the cerebral hemispheres and within certain subcortical and brain-stem nuclear areas. At the ultrastructural level, tangles and plaque neurites contain paired helical filaments whose composition is unknown but may include altered cytoskeletal elements. Amyloid, deposited in plaque cores and often focally present within the cerebral vasculature, contains a polypeptide ("beta-protein," or "beta-amyloid") encoded by a chromosome 21 gene. At least in occasional families, AD has been linked to a separate chromosome 21 locus, but different underlying genetic factors may operate in other cases. Inorganic substances, including aluminum and silicon, are reported to co-localize within tangle-bearing neurons and plaque cores. Specific environmental agents have not been confirmed to be pathogenetically important, however, but may eventually prove to exert a permissive, facilitatory, or even causative role in many AD patients.

Cellular and molecular biology of Alzheimer's disease

Alzheimer's disease results from the degeneration of neurons. Degenerating nerve cells express atypical proteins, and amyloid is deposited. We suggest that some of these events are strongly influenced by genetic factors and age. Animal models should be useful in investigating the pathogenic mechanisms that lead to the brain abnormalities seen in this disease.

Murine trisomy 16 model of Down's syndrome: central nervous system electron microscopic observations

Murine trisomy 16 is an excellent model for the human Down's syndrome (DS). Electron microscopic (EM) observations were made of the cortical plate within the developing telencephalic vesicle at the gestational age of E17. The EM observations revealed: (A) microtubular profiles which were more coiled and curved in the trisomic condition; (B) poor cell-to-cell apposition and increased cellular membrane fragmentation in trisomy 16; (C) increased nuclear contour irregularity in trisomic neurons; (D) significant decrease in the cross-sectional area of neuronal nuclei in trisomy 16 (p less than 0.01). The microtubular observations lend credence to the hypothesis that abnormal cytoskeletal interactions may underlie the mental deficiency seen in DS and may predispose to the eventual development of Alzheimer's disease (AD) in DS individuals. The cellular membrane findings may be related to reported CNS membrane lipid abnormalities in DS. The nuclear morphologic observations may be related to the reported differences in chromatin and nuclear histone expression in AD. These results strengthen the role of the trisomy 16 mouse as a model for DS and potentially for AD.

The pathology of the amyloid A4 precursor of Alzheimer's disease

The A4 amyloid protein is the major subunit present in the amyloid of Alzheimer's disease. It is derived by proteolytic cleavage from a larger precursor (PreA4) which is a neuronal membrane glycoprotein. Whereas in Down's syndrome, over-expression of the gene coding for PreA4 is likely to be responsible for the premature development of cerebral amyloidosis, a similar mechanism is yet to be demonstrated in Alzheimer's disease.

The deposition of amyloid proteins in the aging mammalian brain: implications for Alzheimer's disease

Dysfunction and loss of neurons and their processes in Alzheimer's disease is accompanied by the progressive accumulation of intraneuronal and extracellular proteinaceous filaments. Currently available evidence indicates that the principal confirmed constituent of the intraneuronal paired helical filaments (PHF) is the microtubule-associated protein, tau. Whether other neuronal proteins contribute to the PHF remains unresolved. The amyloid filaments found in cerebral and meningeal microvessels and in the centers of senile plaques appear so far to be protein chemically and immunochemically distinct from the intraneuronal PHF. The native precursor of the beta-amyloid protein comprising these amyloid filaments has now been identified and characterized in brain, non-neural tissues and cDNA-transfected cells of several species, including humans. It occurs as a heterogeneous group of approximately 105-135 kD membrane-associated proteins. cDNA-transfected cells reproduce certain beta-amyloid precursor fragment patterns observed in human brain tissue, including a favored and stable 11 kd fragment containing the carboxyl terminus and presumably the beta-amyloid region. Circulating forms of the precursor have been specifically detected in human cerebrospinal fluid. Understanding the processing of the beta-amyloid precursor protein and the origin of beta-amyloid deposits should provide insights into a potentially seminal feature of cortical degeneration in Alzheimer's disease.

The genetics of Alzheimer's disease

Genetic factors play a major role in some if not all cases of Alzheimer's disease (AD). In certain rare families, the disease is most likely inherited as an autosomal dominant trait. Identification of the genes involved in AD is in progress. One AD-related gene, which codes for the amyloid precursor protein (APP), has been cloned and characterized. This gene, though certainly involved in the pathogenesis of AD, is not defective in AD subjects. Genetic linkage analysis of familial Alzheimer's disease (FAD) should help to identify defective genes directly involved in initiating the pathogenesis of AD. In addition, the study of the genes responsible for the Down syndrome (DS) phenotype may yield information on the sequence of events leading to the dementia of AD.

Three types of amyloid protein precursor mRNA in human brain: their differential expression in Alzheimer's disease

Three types of amyloid protein precursor (APP) mRNA, produced by alternative splicing, were detected by Northern blotting in human brains, both control and Alzheimer's disease. These mRNAs encode APP695 consisting of 695 amino acids, APP751 harboring a 56 amino acid insert homologous to a Kunitz-type trypsin inhibitor inside APP695, and APP770 containing an additional 19 amino acid insert. Another possible APP mRNA which encodes "APP714" containing a 19 amino acid insert was not found in brain samples tested. Quantitative analysis revealed that, although the relative expression levels of the three mRNAs were variable among individuals, there was no remarkable change in expression of APP695 and APP751 mRNAs in Alzheimer's disease compared with control, but that APP770 mRNA level was elevated significantly in Alzheimer's disease.

Longitudinal study of platelet membrane fluidity in Alzheimer's disease

Increased platelet membrane fluidity identifies a prominent subgroup of patients with Alzheimer's disease who exhibit distinct clinical features. In the current longitudinal study, the stability of this membrane characteristic was determined for 15 patients with Alzheimer's disease and 10 healthy elderly controls over a 1-year follow-up period.

Human ETS2 gene on chromosome 21 is not rearranged in Alzheimer disease

The human ETS2 gene, a member of the ETS gene family, with sequence homology with the retroviral ets sequence of the avian erythroblastosis retrovirus E26 is located on chromosome 21. Molecular genetic analysis of Down syndrome (DS) patients with partial trisomy 21 allowed us to reinforce the supposition that ETS2 may be a gene of the minimal DS genetic region. It was originally proposed that a duplication of a portion of the DS region represents the genetic basis of Alzheimer disease, a condition associated also with DS. No evidence of either rearrangements or duplications of ETS2 could be detected in DNA from fibroblasts and brain tissue of Alzheimer disease patients with either the sporadic or the familiar form of the disease. Thus, an altered ETS2 gene dosage does not seem to be a genetic cause or component of Alzheimer disease.

The senile dementias: a new model

Kuru and Creutzfeldt Jakob disease are fatal neurological disorders in humans that are transmissible to humans and other experimental animals. Largely because of their transmissibility the etiology of these diseases has been ascribed to infectious agents classified as "slow" or unconventional viruses. A related neurological disease in sheep called scrapie has also been ascribed to infection by slow viruses. Despite more than 20 years of intensive research no viruses or other infectious agents have ever been isolated or identified as the causative factors in these transmissible neurological diseases. The model presented below suggests that these "subacute spongiform virus encephalopathies" are not due to any infectious agent. Rather, I propose that they are caused by peptide hormones that may be transmitted from one individual to another in blood or other tissue. These hormones are postulated to activate genes in neurons whose proteins result in the observed pathology. It also is suggested that other non-transmissible human neurological diseases such as Alzheimer's disease may be due to endogenously produced peptide hormones that progressively activate genes responsible for the synthesis of amyloid proteins that are associated with neurological diseases.

Absence of mutation in the beta-amyloid cDNAs cloned from the brains of three patients with sporadic Alzheimer's disease

Using an oligonucleotide probe, we isolated cDNA clones corresponding to the precursor of the beta-amyloid peptide (BAP) from brain libraries of 3 patients with sporadic Alzheimer's disease (AD). DNA sequencing showed that the largest cDNA clone encompasses 83% of the open reading frame proposed by Kang et al. to encode the BAP precursor (APP). cDNA clones from each of the 3 AD brain libraries were identical to the sequence of the APP-cDNAs cloned from normal adult human and fetal brain. An antisense-radiolabeled RNA copy of one of the AD clones detected a pattern of 3 gene transcripts measuring 3.5, 3.2 and 1.6 kilobases (kb) in both normal and AD brain RNAs. These data suggest that there are no mutations in or about the 42 amino acid (aa) sequence of BAP and that the accumulation of amyloid consistently found in AD may result from altered post-translational processing of APP.

Neuroplasticity and the progression of Alzheimer's disease

A neurobiological hypothesis is proposed to explain the relation between the percentage cell loss in the cholinergic basal forebrain and the density of neuritic plaques in cortex, as found by Arendt et al. (1985) in Alzheimer's disease: When cells in the cholinergic basal forebrain die, their cortical synaptic target sites can be reoccupied by axonal sprouting of other neurons from the basal forebrain. This neuroplasticity hypothesis leads to equations that are consistent with the quantitative data of Arendt et al. (1985), and it makes specific predictions that can be tested experimentally. Moreover, this hypothesis suggests that the more rapid course of the presenile form of Alzheimer's disease and its more extensive pathology can be understood as a consequence of the decline in neuroplasticity with age.

Risk factors and genetic background for Alzheimer's disease

Analytic epidemiology has contributed significantly to the generation and testing of hypotheses of the causes of AD. Several case-control studies have indicated risk factors related to the genetic hypothesis, such as: the presence of cases of either AD or Down's syndrome in other family members and the advanced age of the mother at subject's birth. In this respect recent molecular biology studies on DNA from patients affected by the familial form of AD, have demonstrated a genetic polymorphism localized on chromosome 21. On the same chromosome, the gene coding for beta-amyloid has been also recently localized. Immune, viral and toxic factors, thought to cause AD, have been also investigated in case-control studies, none of them has been found consistently associated with the disease, with the only exception of the head trauma. On the other hand most case-control studies have been carried out in younger cases and no large studies are yet available for late onset patients.

Expression of the 210 kDa neurofilament subunit in cultured central nervous system from normal and trisomy 16 mice: regulation by interferon

When applied to central nervous system (CNS) cultures taken from normal fetal mice, interferon increases the immunohistochemical expression of the highly phosphorylated 210 kDa neurofilament subunit. This effect can be blocked by the application of an agent which inhibits interferon-mediated metabolic pathways. Murine trisomy 16 is an excellent model for human Down's Syndrome. CNS cultures taken from trisomy 16 fetal mice express greater intensity of 210 kDa neurofilament subunit immunohistochemical staining than do normals. Application of an interferon inhibitor normalizes trisomy 16 CNS neurofilament expression.

Chromosome localization and polymorphism of an oestrogen-inducible gene specifically expressed in some breast cancers

The BCEI gene codes for a small secreted protein and is expressed in the human mammary tumour cell line MCF7 under oestrogen control and in some breast cancers. We have mapped the gene to chromosome 21 using a panel of somatic hybrid lines, and in situ hybridization has allowed a precise assignment to band 21q223. Two restriction fragment length polymorphisms (RFLP) are described that should be of use in linkage or population studies to test a possible involvement of the BCEI gene in genetic predisposition to breast cancer. This gene should also be a useful marker for the genetic and physical mapping of chromosome 21, and for a better definition of the region involved in the clinical phenotype of Downs syndrome.

Identification in rodents and other species of an mRNA homologous to the human beta-amyloid precursor

The isolation and sequencing of the core peptide (beta-amyloid) found in the plaques of patients with Alzheimer's disease has allowed the identification of a cDNA for the precursor protein. Using a human cDNA clone for this beta-amyloid material, we have identified an homologous mRNA (3.8 kb) in brain tissue obtained from 8 additional species. We have also determined its distribution in 7 brain regions and 12 organs obtained from rodents. A prominent, second mRNA species (2.2 kb) has been identified in rat non-neuronal tissues. The beta-amyloid gene is amply expressed in the brain of all vertebrates tested and in most rodent organs, indicating that it encodes a highly conserved and ubiquitous protein.

Neuroanatomical localization and quantification of amyloid precursor protein mRNA by in situ hybridization in the brains of normal, aneuploid, and lesioned mice

Amyloid precursor protein mRNA was localized in frozen sections from normal and experimentally lesioned adult mouse brain and from normal and aneuploid fetal mouse brain by in situ hybridization with a 35S-labeled mouse cDNA probe. The highest levels of hybridization in adult brain were associated with neurons, primarily in telencephalic structures. The dense labeling associated with hippocampal pyramidal cells was reduced significantly when the cells were eliminated by injection of the neurotoxin ibotenic acid but was not affected when electrolytic lesions were placed in the medial septum. Since the gene encoding amyloid precursor protein has been localized to mouse chromosome 16, we also examined the expression of this gene in the brains of mouse embryos with trisomy 16 and trisomy 19 at 15 days of gestation. RNA gel blot analysis and in situ hybridization showed a marked increase in amyloid precursor protein mRNA in the trisomy 16 mouse head and brain when compared with euploid littermates or with trisomy 19 mice.

Alzheimer's disease amyloidogenic glycoprotein: expression pattern in rat brain suggests a role in cell contact

The cloned cDNA encoding the rat cognate of the human A4 amyloid precursor protein was isolated from a rat brain library. The predicted primary structure of the 695-amino acid-long protein displays 97% identity to its human homologue shown previously to resemble an integral membrane protein. The protein was detected in rodent brain and muscle by Western blot analysis. Using in situ hybridization and immunocytochemistry on rat brain sections, we discovered that rat amyloidogenic glycoprotein (rAG) and its mRNA are ubiquitously and abundantly expressed in neurons indicating a neuronal original for the amyloid deposits observed in humans with Alzheimer's disease (AD). The protein appears in patches on or near the plasma membranes of neurons suggesting a role for this protein in cell contact. Highest expression was seen in rat brain regions where amyloid is deposited in AD but also in areas which do not contain deposits in AD. Since amyloid deposits are rarely observed in rat brain, we conclude that high expression of AG is not the sole cause of amyloidosis.

Expression of ETS proto-oncogenes in astrocytes in human cortex

In order to investigate a possible function of ETS proto-oncogenes in human brain, we incubated a polyclonal antibody raised against the viral region of E26 homologous to ETS1 and ETS2 with human brain frontal cortex sections. Our results show that this antibody decorates astrocytes but not neurons. By using astrocytomas of different grades as a source of astrocytes, we demonstrate the presence of ETS1 and ETS2 messenger RNAs and proteins. This leads to the idea that ETS genes are expressed in cells with dividing potentialities in human cortex and that they could provide a new marker for glial cells. Recently, a microduplication on chromosome 21 including ETS2 locus was described in karyotypically 'normal' Down's syndrome and suspected in Alzheimer's disease; when testing Alzheimer's disease-affected brain cortex sections, no obvious difference was observed with the technique used.

Molecular and genetic investigations on Alzheimer brain amyloid

Amyloid-containing plaques are a characteristic feature of the Alzheimer's disease brain and have been the object of study for decades. Only recently, however, have molecular and genetic techniques been applied to examination of amyloid in order to understand the factors that contribute to the accumulation of plaques in dementia. Current investigations have focused on the structure and properties of the amyloid protein, its corresponding messenger RNA, its cellular site of production, and its chromosomal site of origin. These data are discussed in the present review.

Molecular cloning of amyloid cDNA derived from mRNA of the Alzheimer disease brain: coding and noncoding regions of the fetal precursor mRNA are expressed in the cortex

To gain insight into factors associated with the excessive accumulation of beta-amyloid in the Alzheimer disease (AD) brain, the present studies were initiated to distinguish between a unique primary structure of the AD-specific amyloid precursor mRNA vis a vis other determinants that may affect amyloid levels. Previous molecular cloning experiments focused on amyloid derived from sources other than AD cases. In the present work, we cloned and characterized amyloid cDNA derived directly from AD brain mRNA. Poly(A)+ RNA from AD cortices was used for the preparation of lambda gt11 recombinant cDNA libraries. An insert of 1564 nucleotides was isolated that included the beta-amyloid domain and corresponded to 75% of the coding region and approximately equal to 70% of the 3'-noncoding region of the fetal precursor amyloid cDNA reported by others. On RNA blots, the AD amyloid mRNA consisted of a doublet of 3.2 and 3.4 kilobases. In control and AD cases, the amyloid mRNA levels were nonuniform and were independent of glial-specific mRNA levels. Based on the sequence analysis data, we conclude that a segment of the amyloid gene is expressed in the AD cortex as a high molecular weight precursor mRNA with major coding and 3'-noncoding regions that are identical to the fetal brain gene product.

In situ hybridization of nucleus basalis neurons shows increased beta-amyloid mRNA in Alzheimer disease

To determine which cells within the brain produce beta-amyloid mRNA and to assess expression of the beta-amyloid gene in Alzheimer disease, we analyzed brain tissue from Alzheimer and control patients by in situ hybridization. Our results demonstrate that beta-amyloid mRNA is produced by neurons in the nucleus basalis of Meynert and cerebral cortex and that nucleus basalis perikarya from Alzheimer patients consistently hybridize more beta-amyloid probe than those from controls. These observations support the hypothesis that increased expression of the beta-amyloid gene plays an important role in the deposition of amyloid in the brains of patients with Alzheimer disease.

Differential regulation of amyloid-beta-protein mRNA expression within hippocampal neuronal subpopulations in Alzheimer disease

We have mapped the neuroanatomical distribution of amyloid-beta-protein mRNA within neuronal subpopulations of the hippocampal formation in the cynomolgus monkey (Macaca fascicularis), normal aged human, and patients with Alzheimer disease. Amyloid-beta-protein mRNA appears to be expressed in all hippocampal neurons, but at different levels of abundance. In the central nervous system of monkey and normal aged human, image analysis shows that neurons of the dentate gyrus and cornu Ammonis fields contain a 2.5-times-greater hybridization signal than is present in neurons of the subiculum and entorhinal cortex. In contrast, in the Alzheimer disease hippocampal formation, the levels of amyloid-beta-protein mRNA in the cornu Ammonis field 3 and parasubiculum are equivalent. These findings suggest that within certain neuronal subpopulations cell type-specific regulation of amyloid-beta-protein gene expression may be altered in Alzheimer disease.

Impaired neurotransmitter uptake in PC12 cells overexpressing human Cu/Zn-superoxide dismutase--implication for gene dosage effects in Down syndrome

Rat PC12 cells expressing elevated levels of transfected human Cu/Zn-superoxide dismutase (CuZn-SOD) gene were generated. These transformants (designated PC12-hSOD) closely resembled the parental cells in their morphology, growth rate, and response to nerve growth factor, but showed impaired neurotransmitter uptake. The lesion was localized to the chromaffin granule transport mechanism. We found that the pH gradient (delta pH) across the membrane, which is the main driving force for amine transport, was diminished in PC12-hSOD granules. These results show that elevation of CuZnSOD activity interferes with the transport of biogenic amines into chromaffin granules. Since neurotransmitter uptake plays an important role in many processes of the central nervous system, CuZnSOD gene-dosage may contribute to the neurobiological abnormalities of Down's syndrome.

Amyloid beta-protein gene duplication is not common in Alzheimer's disease: analysis by polymorphic restriction fragments

The amyloid beta-protein(BP) is an important component of amyloid fibrils of both Alzheimer's disease(AD) and adult Down syndrome(DS). It has been hypothesized that sporadic AD may involve the duplication of a subregion of chromosome 21 containing the BP locus. However, an improved method for detection of the BP gene duplication using polymorphic Hind III fragments led us to a conclusion that BP gene duplication is rare, if any, in (Japanese) sporadic AD patients, indicating that the duplication of the BP gene itself is not the common underlying genetic defect in AD.

Beta-amyloid gene dosage in Alzheimer's disease

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Cloning of the cDNA from normal brain and brain of patients with Alzheimer's disease in the expression vector lambda GT 11

1. RNA was purified from postmortem human brains, and the poly A+ RNA was isolated by oligo dT cellulose. 2. Double stranded cDNA was synthesized using reverse transcriptase, RNAse H and DNA polymerase. 3. cDNA was cloned in the lambda GT 11 expression vector, and libraries containing between 1 and 2 millions clones were obtained. 92 to 98% of the plaques contained a recombinant phage. 4. Such libraries will allow the molecular characterization of cDNA and corresponding proteins which play a key role in brain functions and in particular which could be involved in the etiology of Alzheimer's dementia.