Cloning of a gene bearing missense mutations in early-onset familial Alzheimer's disease

Rate of progression in familial Alzheimer's disease

The clinical course of early-onset, dominantly inherited, familial Alzheimer's disease (FAD) was contrasted with late-onset, sporadic Alzheimer's disease (AD). Eight FAD and 23 sporadic AD patients were followed over a mean of 63 months from estimated disease onset. The two groups did not differ notably in duration of symptoms from onset, global disease severity, or degree of cognitive deficits on initial evaluation. The Kaplan-Meier lifetable method was used to assess time from estimated disease onset to dependence in self-care, institutionalization, and death. A greater percentage of FAD patients became dependent in self-care and died earlier than did sporadic AD patients. The lifetable results suggest that FAD may have a more rapid course than dose late-onset sporadic AD.

Molecular biology of APO E alleles in Alzheimer's and non-Alzheimer's dementias

Current research into the aetiology of the dementias is focused upon genetic factors which give rise to the disease process. Recently the Apolipoprotein E gene (APO E) and in particular the epsilon 4 allele has been shown to be a risk factor for late onset Alzheimer's disease (AD) where there is an increased frequency of the epsilon 4 allele. The epsilon 4 allele has also been shown to reduce the age at onset of dementia in AD in a dose dependent manner, with the epsilon 2 allele having an opposing effect. We have genotyped a large series of clinically and neuropathologically confirmed cases of AD and found the expected increase in the Apolipoprotein epsilon 4 allele frequency when compared to a control population. Similarly, in Lewy Body Dementia (LBD) an increased epsilon 4 frequency is also found though a normal epsilon 2 frequency exists, unlike in AD where the epsilon 2 frequency is reduced. No changes in APO E allele frequencies were found in presenile AD, Parkinson's disease with or without dementia, or in Down's syndrome. No association was found between any of the APO E alleles and the histopathological indices of AD, cortical senile plaques and neurofibrillary tangles, in any disease category. Neurochemical indicators of AD, loss of choline acetyltransferase activity was also unaffected by APO E genotype. Whilst their appears to be a strong association between the APO E allele and AD and also in LBD, other related neurodegenerative disorders associated with dementia do not show such a linkage. Changes in the epsilon 2 allele frequency may indicate a genetic difference between AD and LBD. The epsilon 4 allele does not appear to influence the burden of AD type pathology and this is particularly relevant given the relative lack of NFT in LBD indicating that factors other than SP or NFT may govern the onset of dementia.

Progress in Molecular Genetics of Alzheimer's Disease

Recent intensive work has highlighted the genetic basis of several forms of Alzheimer's disease (AD). Mutations in the amyloid precursor protein gene on chromosome 21 can cause either an early-onset autosomal dominant AD or hereditary cerebral hemorrhage with amyloidosis. On chromosome 14, a second gene associated with 70 to 90% early-onset familial AD (FAD) was identified by positional cloning in 1995. Still other kindreds show no linkage to either chromosome 21 or chromosome 14; the third locus (on chromosome 1) was recently identified in affected descendants of a group of families known as the Volga Germans. In late-onset (age >65 years) AD, the apolipoprotein E gene allele ∊e4 on chromosome 19 has clearly been shown to be a risk factor for the development of AD and appears to modify the age of onset of the disease. The emerging picture is that AD is a genetically complex, heterogeneous disorder. Precisely how these genetic factors interact with each other and with other yet-to-be-identified genetic and nongenetic (environmental) factors to produce the clinical and pathologic findings in AD remains to be elucidated. The Neuroscientist 2:3–6, 1996

Improving the robustness of the weighted pairwise correlation test for linkage analysis

The weighted pairwise correlation (WPC) approach provides simple and flexible tests for genetic linkage which may be adapted to qualitative, quantitative, or age-dependent traits. These tests also seem to have good power. However, when working with large pedigrees, a disease susceptibility gene not linked to the marker studied induces correlations of the trait values, leading to inflated type-I errors for these tests. Thus, in its first version, the WPC approach is reliable when using sibships but not when using larger pedigrees. We propose a way for correcting the variances of the WPC statistics to take these correlations into account. A simulation study shows that the type I errors of the corrected statistics are good. The approach is based on a transformation which yields uncorrelated residuals. We study three statistics, based on the permutation distributions of residuals: one based on ordinary residuals adapted to quantitative traits, another based on martingale residuals adapted to survival data, and one based on rank residuals which can be used in both situations. We apply the corrected WPC tests to pedigrees of Alzheimer's disease previously analyzed with the first version of the method (WRPC).

The regions of the Fe65 protein homologous to the phosphotyrosine interaction/phosphotyrosine binding domain of Shc bind the intracellular domain of the Alzheimer's amyloid precursor protein

Fe65 is a protein mainly expressed in several districts of the mammalian nervous system. The search of protein sequence data banks revealed that Fe65 contains two phosphotyrosine interaction (PID) or phosphotyrosine binding (PTB) domains, previously identified in the Shc adaptor molecule. The two putative PID/PTB domains of Fe65 were used to construct glutathione S-transferase-Fe65 fusion proteins. Co-precipitation experiments demonstrated that the Fe65 PID/PTB domains interacted with several proteins of apparent molecular mass 135, 115, 105, and 51 kDa. The region of Fe65 containing the PID/PTB domains was used as a bait to screen a human brain cDNA library in yeast by the two-hybrid system. Three different cDNA clones were isolated, two of which contain overlapping segments of the cDNA encoding the COOH terminus of the Alzheimer's beta-amyloid-precursor protein (APP), that represents the short intracellular domain of this membrane protein. The third clone contains a cDNA fragment coding for the COOH terminus of the human counterpart of a mouse beta-amyloid-like precursor protein. The alignment of the three APP encoding cDNA fragments found in the screening suggests that the region of APP involved in the binding is centered on the NPTY sequence, which is analogous to that present in the intracellular domains of the growth factor receptors interacting with the PID/PTB domain of Shc.

Identification and expression analysis of a potential familial Alzheimer disease gene on chromosome 1 related to AD3

The inheritance of much early-onset Alzheimer disease (AD) has been linked to a dominant-acting locus on chromosome 14. Recently, the gene likely responsible for this genetic linkage has been identified and termed AD3. Five mutations have been found in AD3 that segregate with the disease phenotype in seven AD families and are not present in unaffected individuals. Here we report the existence of a gene encoding a seven transmembrane domain protein very similar to that encoded by AD3 in structure and sequence. This gene is located on chromosome 1, is expressed in a variety of tissues, including brain, and is predicted to harbor mutations causing nonchromosome 14 familial AD. The presence of several S/TPXX DNA binding motifs in both the AD3 protein and the AD3-like protein /AD4 protein suggests a possible role in intracellular signaling and gene expression or in linking chromatin to the nuclear membrane. Ways in which mutations in either gene could lead to AD are discussed.

Failure to detect missense mutations in the S182 gene in a series of late-onset Alzheimer's disease cases

The possibility of an interaction of multiple genes has been speculated in pathogenesis of Alzheimer's disease (AD). Because we have recently cloned a novel gene S182 bearing five different missense mutations which segregate with early-onset familial AD, we sought the frequency of these mutations in familial and sporadic late-onset AD to clarify the incidence of these mutations in the disease. The current study showed lack of these mutations in 118 independent subjects affected with late-onset Alzheimer's disease.

No association found between Alzheimer's disease and a mitochondrial tRNA glutamine gene variant

We have screened a large sample of patients with sporadic late-onset dementia of the Alzheimer type (DAT) and age-matched controls for a mitochondrial tRNA(Gln) variant previously reported to be associated with increased risk of developing Alzheimer's disease (AD). The frequency of an Ava II site gain was determined by restriction analysis of a PCR-amplified mitochondrial DNA product. One of 155 DAT cases and four of 105 age-matched controls carried the variant. Both the affected and control frequencies are statistically different from those previously reported. The mitochondrial lineage of those individuals harboring the variant was determined by sequencing a short region of the hypervariable mitochondrial D-loop. The affected individual and three of the four controls carrying the Ava II variant belong to the same mitochondrial lineage previously reported to be associated with AD.

Genetic susceptibility to Alzheimer disease

Alzheimer disease (AD) is the leading cause of dementia in the elderly. Less than a decade ago, it was questioned as to whether or not genes were even involved in anything but rare early onset AD. Since that time, using a variety of genetic epidemiological and molecular biological techniques, four loci have been identified that play a role in the genetic susceptibility of AD. AD presents as a prototype of the power of genetic techniques in defining the etiology of a complex disease.

Dementia: diagnosis and evaluation

OBJECTIVE

To describe an approach to the diagnosis of dementia based on effective assessment methods.

DESIGN

We reviewed the literature and summarized the available diagnostic and prognostic studies of dementia that may be useful to the primary-care physician.

RESULTS

Although controversy exists about certain aspects of the diagnostic workup, exclusion of potentially reversible causes of dementia is essential. Laboratory studies (for example, for detection of underlying metabolic abnormalities) and neuroimaging of the brain may be useful. The pattern of onset and the temporal course of the disease may suggest a cause and help direct the investigation. Functional losses can substantially impair the patient's ability to live independently.

CONCLUSION

Dementia can be mistakenly considered as part of the normal aging process, and diagnosis necessitates a thorough, although not exhaustive, approach. Early identification of dementing illnesses improves the outcome for reversible disease and may also enhance the management of incurable dementias.

Apolipoprotein E genotype in patients with Alzheimer's disease: implications for the risk of dementia among relatives

Numerous studies have shown that the risk of Alzheimer's disease (AD) is associated with the dose of the epsilon 4 allele of apolipoprotein E (ApoE). However, more than one third of AD patients lack epsilon 4 and many persons having epsilon 4 survive cognitively intact to old age. We evaluated the lifetime risk of disease in 3,999 first-degree relatives of 549 probands who met the criteria for probable or definite AD and whose ApoE genotypes were known. ApoE genotypes for relatives were not determined. After age 65 the risk among relatives was proportional, as much as 7 to 10% at age 85, to the number of epsilon 4 alleles present in the proband. Risks to relatives of ApoE 2/2 and 2/3 probands were nearly identical at all ages to risks for relatives of ApoE 3/3 probands. The expected proportion of relatives having at least one epsilon 4 allele was calculated for each genotype group based on the distribution of parents, sibs, and offspring in the sample. Among relatives in the ApoE 3/3 group, the lifetime risk for AD by age 90 was three times greater than the expected proportion of epsilon 4 carriers, suggesting that factors other than ApoE contribute to AD susceptibility. Furthermore, the 44% risk of AD by age 93 among relatives of ApoE 4/4 probands indicates that as many as 50% of people having at least one epsilon 4 allele do not develop AD. We also found that among male relatives, risk of AD in the ApoE 3/4 group was similar to that for the ApoE 3/3 group but significantly less than the risk for the ApoE 4/4 group. In contrast, among female relatives the risk for the ApoE 3/4 group was nearly twice that for the ApoE 3/3 group and identical to the risk for the ApoE 4/4 group. These findings are consistent with a sex-modification effect of the E4 isoform on disease susceptibility.

Age-related CNS disorder and early death in transgenic FVB/N mice overexpressing Alzheimer amyloid precursor proteins

Transgenic FVB/N mice overexpressing human (Hu) or mouse (Mo) Alzheimer amyloid precursor protein (APP695) die early and develop a CNS disorder that includes neophobia and impaired spatial alternation, with diminished glucose utilization and astrogliosis mainly in the cerebrum. Age at onset of neophobia and age at death decrease with increasing levels of brain APP. HuAPP transgenes induce death much earlier than MoAPP transgenes expressed at similar levels. No extracellular amyloid was detected, indicating that some deleterious processes related to APP overexpression are dissociated from formation of amyloid. A similar clinical syndrome occurs spontaneously in approximately 20% of nontransgenic mice when they reach mid- to late-adult life, suggesting that APP overexpression may accelerate a naturally occurring age-related CNS disorder in FVB/N mice.

Regulated formation of Golgi secretory vesicles containing Alzheimer beta-amyloid precursor protein

Phorbol esters, activators of protein kinase C (PKC), regulate the relative utilization of alternative processing pathways for the Alzheimer beta-amyloid precursor protein (beta-APP) in intact cells, increasing the production of nonamyloidogenic soluble beta-APP (s beta-APP) and decreasing that of neurotoxic beta-amyloid (A beta) peptide. The molecular and cellular bases of PKC-regulated beta-APP cleavage are poorly understood. Here we demonstrate in a reconstituted cell-free system that activation of endogenous PKC increases formation from the trans-Golgi network of secretory vesicles containing beta-APP and that this effect can be mimicked by purified PKC. The results demonstrate directly that PKC is involved in regulation of secretory vesicle formation and provide a mechanism by which PKC may reduce the formation of the A beta peptide characteristic of Alzheimer disease.

GM1 ganglioside-bound amyloid beta-protein (A beta): a possible form of preamyloid in Alzheimer's disease

The earliest event so far known that occurs in the brain affected with Alzheimer's disease (AD) is the deposition and fibril formation of amyloid beta-protein (A beta). A beta is cleaved from a glycosylated membrane protein, called beta-amyloid protein precursor, and normally secreted into the extracellular space. Here we report on the presence of membrane-bound A beta that tightly binds GM1 ganglioside. This suggests that this novel A beta species, rather than secreted A beta, may act as a 'seed' for amyloid and further that intracellular abnormalities in the membrane recycling already exist at the stage of amyloidogenesis.

The structure of the presenilin 1 (S182) gene and identification of six novel mutations in early onset AD families

Genetic linkage studies place a gene causing early onset familial Alzheimer's disease (FAD) on chromosome 14q24.3 (refs 1-4). Five mutations within the S182 (Presenilin 1: PS-1) gene, which maps to this region, have recently been reported in several early onset FAD kindreds. We have localized the PS-1 gene to a 75 kb region and present the structure of this gene, evidence for alternative splicing and describe six novel mutations in early onset FAD pedigrees all of which alter residues conserved in the STM2 (Presenilin 2: PS-2) gene.

Facilitation of lin-12-mediated signalling by sel-12, a Caenorhabditis elegans S182 Alzheimer's disease gene

The lin-12 and glp-1 genes of Caenorhabditis elegans are members of the lin-12/Notch family of receptors for intercellular signals that specify cell fate. By screening for suppressors of a lin-12 gain-of-function mutation, we identified a new gene, sel-12, which appears to function in receiving cells to facilitate signalling mediated by lin-12 and glp-1. The sel-12 gene encodes a protein with multiple transmembrane domains, and is similar to S182, which has been implicated in early-onset familial Alzheimer's disease. The high degree of sequence conservation suggests that the function of the SEL-12 and S182 proteins may also be conserved.

Genetic dissection of Alzheimer disease, a heterogeneous disorder

The genetics of Alzheimer disease (AD) are complex and not completely understood. Mutations in the amyloid precursor protein gene (APP) can cause early-onset autosomal dominant AD. In vitro studies indicate that cells expressing mutant APPs overproduce pathogenic forms of the A beta peptide, the major component of AD amyloid. However, mutations in the APP gene are responsible for 5% or less of all early-onset familial AD. A locus on chromosome 14 is responsible for AD in other early-onset AD families and represents the most severe form of the disease in terms of age of onset and rate of decline. Attempts to identify the AD3 gene by positional cloning methods are underway. At least one additional early-onset AD locus remains to be located. In late-onset AD, the apolipoprotein E gene allele epsilon 4 is a risk factor for AD. This allele appears to act as a dose-dependent age-of-onset modifier. The epsilon 2 allele of this gene may be protective. Other late-onset susceptibility factors remain to be identified.

Amyloid, aluminium and the aetiology of Alzheimer's disease

Several lines of evidence suggest that neurotoxic beta A4 amyloid deposits are of prime importance in the pathogenesis of Alzheimer's disease. Epidemiologically determined risk factors such as Down's syndrome, head injury and apoE allelic status can be explained on the basis of this hypothesis. However, there are difficulties with the hypothesis--amyloid accumulation may be necessary, but is not sufficient to produce the neuronal damage seen in Alzheimer's disease. The association between aluminum exposure and Alzheimer's disease remains unproven and is considered to be increasingly peripheral to recent developments in our understanding of the disease.

The inflammatory response system of brain: implications for therapy of Alzheimer and other neurodegenerative diseases

Cultured brain cells are capable of generating many molecules associated with inflammatory and immune functions. They constitute the endogenous immune response system of brain. They include complement proteins and their regulators, inflammatory cytokines, acute phase reactants and many proteases and protease inhibitors. Most of the proteins are made by microglia and astrocytes, but even neurons are producers. Many appear in association with Alzheimer disease lesions, indicating a state of chronic inflammation in Alzheimer disease brain. Such a state can apparently exist without stimulation by peripheral inflammatory mediators or the peripheral immune system. A strong inflammatory response may be autotoxic to neurons, exacerbating the fundamental pathology in Alzheimer disease and perhaps other neurological disorders. Autotoxic processes may contribute to cellular death in chronic inflammatory diseases affecting other parts of the body, suggesting the general therapeutic value of anti-inflammatory agents. With respect to Alzheimer disease, multiple epidemiological studies indicate that patients taking anti-inflammatory drugs or suffering from conditions in which such drugs are routinely used, have a decreased risk of developing Alzheimer disease. In one very preliminary clinical trial, the anti-inflammatory drug indomethacin arrested progress of the disease. New agents directed against the inflammatory processes revealed in studies of Alzheimer disease lesions may have broad therapeutic applications.

Familial Alzheimer's disease in kindreds with missense mutations in a gene on chromosome 1 related to the Alzheimer's disease type 3 gene

We report the cloning of a novel gene (E5-1) encoded on chromosome 1 which has substantial nucleotide and amino-acid sequence similarity to the S182 gene on chromosome 14q24.3. Mutations, including three new missense mutations in the S182 gene, are associated with the AD3 subtype of early-onset familial Alzheimer's disease (AD). Both the E5-1 and the S182 proteins are predicted to be integral membrane proteins with seven membrane-spanning domains, and a large exposed loop between the sixth and seventh transmembrane domains. Analysis of the nucleotide sequence of the open reading frame (ORF) of the E5-1 gene led to the discovery of two missense substitutions at conserved amino-acid residues in affected members of pedigrees with a form of familial AD that has a later age of onset than the AD3 subtype (50-70 years versus 30-60 years for AD3). These observations imply that the E5-1 gene on chromosome 1 and the S182 gene on chromosome 14q24.3 are members of a family of genes (presenilins) with related functions, and indicates that mutations in conserved residues of E5-1 could also play a role in the genesis of AD. Our results also indicate that still other AD susceptibility genes exist.

A familial Alzheimer's disease locus on chromosome 1

The Volga German kindreds are a group of seven related families with autosomal dominant early-onset Alzheimer's disease (AD). Linkage to known AD-related loci on chromosomes 21 and 14 has been excluded. Significant evidence for linkage to AD in these families was obtained with D1S479 and there was also positive evidence for linkage with other markers in the region. A 112-base pair allele of D1S479 co-segregated with the disease in five of seven families, which is consistent with a common genetic founder. This study demonstrates the presence of an AD locus on chromosome 1q31-42.

Candidate gene for the chromosome 1 familial Alzheimer's disease locus

A candidate gene for the chromosome 1 Alzheimer's disease (AD) locus was identified (STM2). The predicted amino acid sequence for STM2 is homologous to that of the recently cloned chromosome 14 AD gene (S182). A point mutation in STM2, resulting in the substitution of an isoleucine for an asparagine (N141l), was identified in affected people from Volga German AD kindreds. This N141l mutation occurs at an amino acid residue that is conserved in human S182 and in the mouse S182 homolog. The presence of missense mutations in AD subjects in two highly similar genes strongly supports the hypothesis that mutations in both are pathogenic.