Phenotype of chromosome 14-linked familial Alzheimer's disease in a large kindred

The Helico Maze Detects Early Impairment of Reference Memory at Three Months of Age in the 5XFAD Mouse Model of Alzheimer’s Disease

Background: The 5XFAD model of Alzheimer’s disease (AD) bearing five familial mutations of Alzheimer’s disease on human APP and PSEN1 transgenes shows deposits of amyloid-β peptide (Aβ) as early as 2 months, while deficits in long-term memory can be detected at 4 months using the highly sensitive olfactory-dependent tests that we previously reported. Objective: Given that detecting early dysfunctions in AD prior to overt pathology is of major interest in the field, we sought to detect memory deficits at earlier stages of the disease in 3-month-old male 5XFAD mice. Methods: To this end, we used the Helico Maze, a behavioral task that was recently developed and patented. This device allows deeper analysis of learning and subcategories of hippocampal-dependent long-term memory using olfactory cues. Results: Eight male 5XFAD and 6 male wild-type (WT: C57Bl6 background) mice of 3 months of age were tested in the Helico Maze. The results demonstrated, for the first time, a starting deficit of pure reference long-term memory. Interestingly, memory impairment was clearly correlated with Aβ deposits in the hippocampus. While we also found significant differences in astrogliosis between 5XFAD and WT mice, this was not correlated with memory abilities. Conclusion: Our results underline the efficiency of this new olfactory-dependent behavioral task, which is easy to use, with a small cohort of mice. Using the Helico Maze may open new avenues to validate the efficacy of treatments that target early events related to the amyloid-dependent pathway of the disease and AD progression.

Corticobasal Syndrome in a Family with Early-Onset Alzheimer's Disease Linked to a Presenilin-1 Gene Mutation

BACKGROUND

Alzheimer's disease (AD) is the second-most frequent cause underlying corticobasal syndrome (CBS). However, a reliable diagnosis using clinical, neuropsychological, or neuroimaging approaches has not yet been achieved.

METHODS

Clinical, neuropsychological, imaging, and neuropathology studies were undertaken in a large Spanish family with early-onset familial AD (EOFAD) carrying a Met233Leu mutation linked to presenilin-1 gene (PSEN-1).

RESULTS

Two of three examined members of this family presented with the usual amnestic pattern. At the age of 47 years, a third family member, in whom pathology was later confirmed, developed prominent CBS combined with severe neuropsychiatric and behavioral disturbances resembling those often found in EOFAD.

CONCLUSION

Although CBS in EOFAD appears to be rare, demonstration of a linkage to PSEN-1 gene mutations may permit in vivo diagnosis.

Impaired default network functional connectivity in autosomal dominant Alzheimer disease

OBJECTIVE

To investigate default mode network (DMN) functional connectivity MRI (fcMRI) in a large cross-sectional cohort of subjects from families harboring pathogenic presenilin-1 (PSEN1), presenilin-2 (PSEN2), and amyloid precursor protein (APP) mutations participating in the Dominantly Inherited Alzheimer Network.

METHODS

Eighty-three mutation carriers and 37 asymptomatic noncarriers from the same families underwent fMRI during resting state at 8 centers in the United States, United Kingdom, and Australia. Using group-independent component analysis, fcMRI was compared using mutation status and Clinical Dementia Rating to stratify groups, and related to each participant's estimated years from expected symptom onset (eYO).

RESULTS

We observed significantly decreased DMN fcMRI in mutation carriers with increasing Clinical Dementia Rating, most evident in the precuneus/posterior cingulate and parietal cortices (p < 0.001). Comparison of asymptomatic mutation carriers with noncarriers demonstrated decreased fcMRI in the precuneus/posterior cingulate (p = 0.014) and right parietal cortex (p = 0.0016). We observed a significant interaction between mutation carrier status and eYO, with decreases in DMN fcMRI observed as mutation carriers approached and surpassed their eYO.

CONCLUSION

Functional disruption of the DMN occurs early in the course of autosomal dominant Alzheimer disease, beginning before clinically evident symptoms, and worsening with increased impairment. These findings suggest that DMN fcMRI may prove useful as a biomarker across a wide spectrum of disease, and support the feasibility of DMN fcMRI as a secondary endpoint in upcoming multicenter clinical trials in Alzheimer disease.

New genes and new insights from old genes: update on Alzheimer disease

PURPOSE OF REVIEW

This article discusses the current status of knowledge regarding the genetic basis of Alzheimer disease (AD) with a focus on clinically relevant aspects.

RECENT FINDINGS

The genetic architecture of AD is complex, as it includes multiple susceptibility genes and likely nongenetic factors. Rare but highly penetrant autosomal dominant mutations explain a small minority of the cases but have allowed tremendous advances in understanding disease pathogenesis. The identification of a strong genetic risk factor, APOE, reshaped the field and introduced the notion of genetic risk for AD. More recently, large-scale genome-wide association studies are adding to the picture a number of common variants with very small effect sizes. Large-scale resequencing studies are expected to identify additional risk factors, including rare susceptibility variants and structural variation.

SUMMARY

Genetic assessment is currently of limited utility in clinical practice because of the low frequency (Mendelian mutations) or small effect size (common risk factors) of the currently known susceptibility genes. However, genetic studies are identifying with confidence a number of novel risk genes, and this will further our understanding of disease biology and possibly the identification of therapeutic targets.

Regional brain volume differences in symptomatic and presymptomatic carriers of familial Alzheimer's disease mutations

BACKGROUND

Mutations in the presenilin (PSEN1, PSEN2) and amyloid precursor protein (APP) genes cause familial Alzheimer's disease (FAD) in a nearly fully penetrant, autosomal dominant manner, providing a unique opportunity to study presymptomatic individuals who can be predicted to develop Alzheimer's disease (AD) with essentially 100% certainty. Using tensor-based morphometry (TBM), we examined brain volume differences between presymptomatic and symptomatic FAD mutation carriers and non-carrier (NC) relatives.

METHODS

Twenty-five mutation carriers and 10 NC relatives underwent brain MRI and clinical assessment. Four mutation carriers had dementia (MUT-Dem), 12 had amnestic mild cognitive impairment (MUT-aMCI) and nine were cognitively normal (MUT-Norm). TBM brain volume maps of MUT-Norm, MUT-aMCI and MUT-Dem subjects were compared to NC subjects.

RESULTS

MUT-Norm subjects exhibited significantly smaller volumes in the thalamus, caudate and putamen. MUT-aMCI subjects had smaller volumes in the thalamus, splenium and pons, but not in the caudate or putamen. MUT-Dem subjects demonstrated smaller volumes in temporal, parietal and left frontal regions. As non-demented carriers approached the expected age of dementia diagnosis, this was associated with larger ventricular and caudate volumes and a trend towards smaller temporal lobe volume.

CONCLUSIONS

Cognitively intact FAD mutation carriers had lower thalamic, caudate and putamen volumes, and we found preliminary evidence for increasing caudate size during the predementia stage. These regions may be affected earliest during prodromal stages of FAD, while cortical atrophy may occur in later stages, when carriers show cognitive deficits. Further studies of this population will help us understand the progression of neurobiological changes in AD.

Comparison of clinical characteristics between familial and non-familial early onset Alzheimer's disease

Although familial Alzheimer's disease (FAD) is an early onset AD (EAD), most patients with EAD do not have a familial disorder. Recent guidelines recommend testing for genes causing FAD only in those EAD patients with two first-degree relatives. However, some patients with FAD may lack a known family history or other indications for suspecting FAD but might nonetheless be carriers of FAD mutations. The study was aimed to identify clinical features that distinguish FAD from non-familial EAD (NF-EAD). A retrospective review of a university-based cohort of 32 FAD patients with PSEN1-related AD and 81 with NF-EAD was conducted. The PSEN1 patients, compared to the NF-EAD patients, had an earlier age of disease onset (41.8 ± 5.2 vs. 55.9 ± 4.8 years) and, at initial assessment, a longer disease duration (5.1 ± 3.4 vs. 3.3 ± 2.6 years) and lower MMSE scores (10.74 ± 8.0 vs. 20.95 ± 5.8). Patients with NF-EAD were more likely to present with non-memory deficits, particularly visuospatial symptoms, than were FAD patients. When age, disease duration, and MMSE scores were controlled in a logistical regression model, FAD patients were more likely to have significant headaches, myoclonus, gait abnormality, and pseudobulbar affect than those with NF-EAD. In addition to a much younger age of onset, FAD patients with PSEN1 mutations differed from those with NF-EAD by a history of headaches and pseudobulbar affect, as well as myoclonus and gait abnormality on examination. These may represent differences in pathophysiology between FAD and NF-EAD and in some contexts such findings should lead to genetic counseling and appropriate recommendations for genetic testing for FAD.

Early-onset familial Alzheimer's disease (EOFAD)

Early-onset familial Alzheimer's disease (EOFAD) is a condition characterized by early onset dementia (age at onset < 65 years) and a positive family history for dementia. To date, 230 mutations in presenilin (PS1, PS2) and amyloid precursor protein (APP) genes have been identified in EOFAD. The mutations within these three genes (PS1/PS2/APP) affect a common pathogenic pathway in APP synthesis and proteolysis, which lead to excessive production of amyloid β. Compared with sporadic Alzheimer's disease (AD), EOFAD has some distinctive features including early age at onset, positive familial history, a variety of non-cognitive neurological symptoms and signs, and a more aggressive course. There is marked phenotypic heterogeneity among different mutations of EOFAD. Studies in presymptomatic mutation carriers reveal biomarkers abnormalities. EOFAD diagnosis is based on clinical and family history, neurological symptoms and examination, biomarker features, as well as genotyping in some cases. New therapeutic agents targeting amyloid formation may benefit EOFAD individuals.

The usefulness of biological and neuroimaging markers for the diagnosis of early-onset Alzheimer's disease

The recent proposed criteria for Alzheimer's Disease (AD) have strongly claimed the usefulness of biological and neuroimaging markers for early identification AD. Cerebrospinal fluid (CSF) Tau/Abeta ratio, hippocampal atrophy, posterior cingulate, and neocortical associative area hypometabolism, or amyloid burden evaluated by PiB compound, held the premises to increase diagnostic accuracy in the preclinical disease stages. Despite many efforts to identify subjects at risk of developing AD, less attention has been paid to presenile AD diagnosis. A few data are already available in early onset AD, mainly obtained in cases of monogenic disorder. In this paper, we discuss the current literature on the role of biological and neuroimaging markers in presenile AD.

Correlating familial Alzheimer's disease gene mutations with clinical phenotype

Alzheimer's disease (AD) causes devastating cognitive impairment and an intense research effort is currently devoted to developing improved treatments for it. A minority of cases occur at a particularly young age and are caused by autosomal dominantly inherited genetic mutations. Although rare, familial AD provides unique opportunities to gain insights into the cascade of pathological events and how they relate to clinical manifestations. The phenotype of familial AD is highly variable and, although it shares many clinical features with sporadic AD, it also possesses important differences. Exploring the genetic and pathological basis of this phenotypic heterogeneity can illuminate aspects of the underlying disease mechanism, and is likely to inform our understanding and treatment of AD in the future.

Cortical event-related potentials in preclinical familial Alzheimer disease

OBJECTIVE

To define changes in cortical function in persons inheriting familial Alzheimer disease (FAD) mutations before the onset of cognitive decline.

METHODS

Twenty-six subjects with a family history of FAD were divided into 2 subgroups according to genotype (FAD mutation carriers, n = 15; FAD noncarriers, n = 11). Subjects were given standardized tests of cognitive function and the Clinical Dementia Rating scale (CDR). Sensory (P50, N100, P200) and cognitive (N200, P300) event-related potentials were recorded during an auditory discrimination task. Amplitudes and latencies of cortical potentials were compared among FAD mutation carriers and noncarriers.

RESULTS

FAD mutation carriers and noncarriers did not significantly differ in age or on measures of cognitive function, but FAD carriers had a greater incidence of 0.5 CDR scores (1/10 noncarriers, 5/15 carriers). Relative to noncarriers, FAD mutation carriers had significantly longer latencies of the N100, P200, N200, and P300 components, and smaller slow wave amplitudes. Subanalyses of subjects having CDR scores of 0.0 also showed latency increases in FAD mutation carriers.

CONCLUSIONS

Auditory sensory and cognitive cortical potentials in persons with familial Alzheimer disease (FAD) mutations are abnormal approximately 10 years before dementia will be manifest. Longer event-related potential latencies suggest slowing of cortical information processing in FAD mutation carriers.

Genetic aspects of Alzheimer disease

Alzheimer disease is the most common cause of dementia and represents a major public health problem. The neuropathologic findings of amyloid-beta plaques and tau containing neurofibrillary tangles represent important molecular clues to the underlying pathogenesis. Genetic factors are well recognized, but complicated. Three rare forms of autosomal-dominant early-onset familial Alzheimer disease have been identified and are associated with mutations in amyloid precursor protein, presenilin 1, and presenilin 2 genes. The more common late-onset form of Alzheimer disease is assumed to be polygenic/multifactorial. However, thus far the only clearly identified genetic risk factor for Alzheimer disease is Apo lipoprotein E. The epsilon4 allele of Apo lipoprotein E influences age at onset of Alzheimer disease, but is neither necessary nor sufficient for the disease. The search continues for the discovery of additional genetic influences.

The Genetics of Very Early Onset Alzheimer Disease

OBJECTIVE

This study was undertaken to clarify the genetics of very early onset Alzheimer disease (VEOAD), defined as AD beginning before age 35.

BACKGROUND

Early onset AD (EOAD) is defined by onset of symptoms before age 65, and affected individuals may harbor a mutation in presenilin 1 (PSEN1), presenilin 2 (PSEN2), or amyloid precursor protein. VEOAD is exceedingly rare, and PSEN1 mutations have been implicated. We encountered a man with phenotypic frontotemporal dementia beginning at age 32 and a strong family history of an autosomal dominant dementia who was found at autopsy to have AD.

METHODS

Histologic and genetic analyses of the patient's brain were undertaken, and a review of all published VEOAD cases was performed.

RESULTS

Histologic findings were diagnostic of advanced stage AD. Genetic evaluation of brain tissue identified an intronic PSEN1 polymorphism; no known pathogenic mutation was found. Literature review (1934 to 2007) disclosed 101 cases of VEOAD; the youngest age of dementia onset was 24 years. In all cases in which definitive genetic analysis was available, either a PSEN1 mutation or linkage to chromosome 14 was found.

CONCLUSIONS

VEOAD can present with atypical clinical features, including findings suggestive of frontotemporal dementia. All reported cases of VEOAD with conclusive genetic analysis seem to be associated with PSEN1 mutations. Genetic testing in adults younger than 35 with dementia can identify the genetic defect and assist in diagnosis and family counseling.

Lewy body pathology in familial Alzheimer disease: evidence for disease- and mutation-specific pathologic phenotype

BACKGROUND

The origin and significance of Lewy bodies and neurites (Lewy body pathology [LBP]) in Alzheimer disease (AD) are poorly understood.

OBJECTIVE

To examine LBP in the brainstem, limbic cortex, and neocortex of a large number of familial AD cases with mutations in 2 presenilin (PSEN) genes.

METHODS

Twenty-five familial AD cases with 9 known PSEN 1 mutations and 14 familial AD cases with a single PSEN 2 mutation (N141I) were examined for LBP using alpha-synuclein immunohistochemistry and sampling of multiple brainstem and cortical regions.

RESULTS

The amygdala was the most vulnerable site for LBP. In fact, virtually all (24 [96%] of 25 cases) of the PSEN 1 mutation cases had LBP in the amygdala. The PSEN 1 mutation cases also had more frequent LBP in the amygdala and neocortex than those with the PSEN 2 mutation. However, within families with a single mutation of either PSEN 1 or PSEN 2, there was frequent variability of the LBP.

CONCLUSION

These findings suggest that there are genetic influences on the presence of LBP in familial AD as demonstrated by the differences between PSEN 1 and PSEN 2 mutation cases.

Genetics, transcriptomics, and proteomics of Alzheimer's disease

OBJECTIVE

To provide an updated overview of the methods used in genetic, transcriptomic, and proteomic studies in Alzheimer's disease and to demonstrate the importance of those methods for the improvement of the current diagnostic and therapeutic possibilities.

DATA SOURCES

MEDLINE-based search of 233 peer-reviewed articles published between 1975 and 2006.

DATA SYNTHESIS

Alzheimer's disease is a genetically heterogeneous disorder. Rare mutations in the amyloid precursor protein, presenilin 1, and presenilin 2 genes have shown the importance of the amyloid metabolism for its development. In addition, converging evidence from population-based genetic studies, gene expression studies, and protein profile studies in the brain and in the cerebrospinal fluid suggest the existence of several pathogenetic pathways such as amyloid precursor protein processing, beta-amyloid degradation, tau phosphorylation, proteolysis, protein misfolding, neuroinflammation, oxidative stress, and lipid metabolism.

CONCLUSIONS

The development of high-throughput genotyping methods and of elaborated statistical analyses will contribute to the identification of genetic risk profiles related to the development and course of this devastating disease. The integration of knowledge derived from genetic, transcriptomic, and proteomic studies will greatly advance our understanding of the causes of Alzheimer's disease, improve our capability of establishing an early diagnosis, help define disease subgroups, and ultimately help to pave the road toward improved and tailored treatments.

Neuropsychological function in nondemented carriers of presenilin-1 mutations

BACKGROUND

Prospective and case-control studies have demonstrated that memory loss and executive dysfunction occur early in Alzheimer disease (AD).

OBJECTIVE

To investigate these observations by the study of persons at risk for autosomal dominant forms of AD.

METHODS

Neuropsychological and genetic tests were performed on 51 nondemented at-risk members of 10 Mexican families with two distinct presenilin-1 (PS1) mutations. Test scores were compared between PS1 mutation carriers (MCs; n = 30) and noncarriers (NCs; n = 21) by analyses of variance, co-varying for family and specific mutation. Regression analyses were performed, taking into account age relative to the median age at dementia diagnosis in the family (adjusted age), gender, Beck Depression Inventory (BDI) scores, education, and number of APOE epsilon4 alleles. Subjects were divided into age tertiles and scores compared within these groups. Composite scores for Verbal Memory, Executive Function/Working Memory, Language, and Visuospatial Function were created, and these scores compared between MCs and NCs.

RESULTS

MCs performed worse than NCs on the Mini-Mental State Examination, Trails Making Tests A and B, Delayed Recall of a 10-Word List, and Wechsler Adult Intelligence Scale WAIS Block Design. In multiple linear regression analyses, BDI score, gender, and number of APOE epsilon4 alleles did not consistently affect test scores. The differences seen between MCs and NCs were due to differences in the oldest tertile. MCs had lower Visuospatial and Executive Function/Working Memory but not Verbal Memory or Language composite scores.

CONCLUSIONS

This study is consistent with findings in sporadic Alzheimer disease of early problems with memory, visuospatial function, and particularly with executive function in PS1 mutation carriers. Depression, gender, and presence of an APOE epsilon4 allele did not demonstrate large influences on neuropsychological performance.

What the study of persons at risk for familial Alzheimer's disease can tell us about the earliest stages of the disorder: a review

As the proportion of elderly persons continues to expand, understanding the pathobiology of Alzheimer's disease and being able to diagnose it at an early stage become more critical. A minority of Alzheimer's disease cases are inherited as a fully-penetrant, autosomal dominant trait with a young age of onset. The molecular study of the pathogenic mutations has led to insights regarding the etiology of sporadic Alzheimer's disease. Clinical studies in persons at risk for these mutations have confirmed early episodic memory and executive deficits in Alzheimer's disease and suggested that dysphoria may precede the cognitive changes of Alzheimer's disease. Imaging studies have indicated that medial temporal lobe atrophy begins 3 to 4 years before cognitive symptoms, and quantitative cerebral metabolic changes are also present from early on. Studies of biochemical markers suggest that elevations of plasma A 1-42 occur early in familial Alzheimer's disease but that tau may not be elevated in cerebrospinal fluid until the disease is more advanced.

Clinical phenotypic heterogeneity of Alzheimer's disease associated with mutations of the presenilin-1 gene

It is now 10 years since the first report of mutations in the presenilin genes that were deterministic for familial autosomal dominant Alzheimer's disease. The most common of these mutations occurs in the presenilin-1 gene (PSEN1) located on chromosome 14. In the ensuing decade, more than 100 PSEN1 mutations have been described. The emphasis of these reports has largely been on the novelty of the mutations and their potential pathogenic consequences rather than detailed clinical, neuropsychological, neuroimaging and neuropathological accounts of patients with the mutation. This article reviews the clinical phenotypes of reported PSEN1 mutations, emphasizing their heterogeneity, and suggesting that other factors, both genetic and epigenetic,must contribute to disease phenotype.

Clinical, pathological, and biochemical spectrum of Alzheimer disease associated with PS-1 mutations

Three genes have been implicated in the etiology of early-onset autosomal-dominant Alzheimer disease (AD): the amyloid precursor protein, the presenilin-1, and presenilin-2 genes. Approximately half of autosomal-dominant AD cases are associated with mutations in the presenilin-1 (PS-1) gene on the long arm of Chromosome 14. Marked allelic heterogeneity characterizes families with PS-1 gene mutations; more than 100 different mutations have been found in independent families thus far. With the exception of age at onset, the clinical phenotype is similar to late-onset AD, although some rare specific phenotypes have been described. These mutations lead to enhanced deposition of total Abeta and Abeta42 (but not Abeta40) in the brain, compared with sporadic AD. There is a considerable heterogeneity in the histological profiles among brains from patients with different mutations, and although some lead to predominantly parenchymal deposition of Abeta in the form of diffuse and cored plaques, others show predominantly vascular deposition, with severe amyloid angiopathy. Only some mutations are associated with enhanced neurofibrillary tangle formation and increased neuronal loss compared with sporadic AD. However, there is an important clinical and pathological variability even among family members with the same mutation, which suggests the involvement of other genetic or environmental factors that modulate the clinical expression of the disease. This represents a valuable model for identifying such factors and has potential implications for the development of new therapeutic strategies for delaying disease onset.

Neuropsychological functions in variant Alzheimer's disease with spastic paraparesis

Few data exist on the effects of specific Alzheimer's disease (AD)-related mutations on cognitive function. We present neuropsychological test results in eight members of a large kindred with variant Alzheimer's disease (VarAD) due to a deletion of the presenilin 1 (PS-1) gene, encompassing exon 9. The disease was neuropathologically characterized by the presence of large, unusual, "cotton wool" plaques (CWP). Four surviving patients were prospectively tested, and retrospective neuropsychological data were collected from additional four deceased patients. The neuropsychological evaluation was based on tests of verbal and visual memory, abstract thinking, and visuoconstructive and spatial functions. In addition, psychiatric symptoms were evaluated. In four patients, brain glucose metabolism was examined by positron emission tomography (PET). PET showed temporoparietal hypometabolism typical of AD. In addition, variable patterns of hypometabolism (hemispherical asymmetry and occipital accentuation) were related to individual deficits of cognitive performance. However, all these early-onset patients (age range 43-63 years) with a deletion mutation of PS-1 gene showed prominent memory impairment and deficits in visuoconstructive and intellectual functions.

Neuropsychological study of familial Alzheimer's disease caused by mutation E280A in the presenilin 1 gene

In Antioquia, Colombia, investigators have recently discovered the largest family with the E280A mutation in the presenilin 1 gene that causes one type of familial Alzheimer's disease (FAD). The current study compares two groups within this family: those diagnosed with Alzheimer's disease (AD) in its early stage (nine subjects) and relatives (carriers) who did not show any signs of dementia (nine subjects). A battery of the following neuropsychological tests was administered to subjects in both groups: the Consortium to Establish a Registry for Alzheimer's Disease (CERAD), a Phonological Verbal Fluency test, the Visual "A" Cancellation Test, memory of three phrases, the Rey-Osterrieth Complex Figure, and the Trail Making Test Part A. Statistical analyses of the average test scores of each group showed that the AD group scored significantly (p < 0.01 or p < 0.05) lower on 29 of the 43 neuropsychological variables measured (67 percent). Therefore, this specific battery was useful in discriminating subjects with AD from their healthy relatives who are carriers of the disease. The AD group as a whole presented slight dementia with predominant deficits in memory, language, praxis, and attention. This profile is similar to those reported in subjects with sporadic AD in its early stage and confirms the findings found in other neuropsychological studies of subjects with FAD linked to mutations in chromosome 14.

Genetics of dementia

Many neurodegenerative diseases are exceedingly complex disorders (Fig. 6). In the past decade, we have made tremendous advances in our understanding [figure: see text] of the genetic basis of these disorders. One common characteristic of these disorders is the existence of rare families in which a given disease is inherited as a Mendelian trait. In this article, we have reviewed the genetics of several common neurodegenerative disorders that are associated with cognitive disturbances and for which causative genes have been identified. Further genetic analysis should clarify the roles of known genes in the pathogenesis of common sporadic forms of these various diseases. Investigation of the normal and aberrant functions of these genes should provide insight into the underlying mechanisms of these disorders. Such research should facilitate new strategies for therapeutic interventions. Although molecular genetics has helped to clarify the etiology of these disorders, clinicians have played a critical role in the careful identification and classification of many families who were involved in the eventual mapping and cloning of causative mutations. The role of the clinician should not be underestimated. Future clinical and molecular genetics findings hold many clinical implications. It is likely that new diagnostic and therapeutic strategies for dementing disorders are just on the horizon.

Cerebellar diffuse amyloid plaques are derived from dendritic Abeta42 accumulations in Purkinje cells

beta-amyloid(1-42) (Abeta42)-rich amyloid plaques (APs) may be derived from destroyed neurons that were burdened with extensive intracellular Abeta42 accumulations. Since most cells that accumulate Abeta42 express the alpha7 nicotinic acetylcholine receptor (alpha7nAChR), we examined the relationship between the intracellular accumulation of Abeta42 and the expression of the alpha7nAChR in cells from the cerebellum of sporadic Alzheimer's disease (AD) patients. Abeta42, but not Abeta40 or Abeta43, accumulates intracellularly in Purkinje, Golgi II, stellate and basket cells in the AD cerebellum, all of which express the alpha7nAChR. Abeta42 deposits were also prominent within dendrites of Purkinje cells, especially at points of their bifurcation that were often occluded with this material. Diffuse APs appeared to represent the remnants of destroyed Abeta42-laden segments of Purkinje cell dendritic trees. Similarly, the accumulation of Abeta42 and early loss of Golgi II cells in AD cerebella correlated directly to their high level of alpha7nAChR expression. Furthermore, the presence and relative abundance of neuron-derived Abeta42/alpha7nAChR-positive materials within Bergman glia may be indicative of the stage of AD. These data are consistent with a role for the alpha7nAChR in mediating intracellular Abeta42 accumulation and also support the notion that the intracellular and intradendritic accumulation of Abeta42 may eventually result in cell lysis and the formation of APs.

Ectopic white matter neurons, a developmental abnormality that may be caused by the PSEN1 S169L mutation in a case of familial AD with myoclonus and seizures

We report clinical, neuropathologic and molecular genetic data from an individual affected by a familial Alzheimer disease (AD) variant. The proband had an onset of dementia at age 29 followed by generalized seizures a year later. He died at age 40. Neuropathologically, he had severe brain atrophy and characteristic histopathologic lesions of AD. Three additional neuropathologic features need to be emphasized: 1) severe deposition of Abeta in the form of diffuse deposits in the cerebral and cerebellar cortices, 2) numerous Abeta deposits in the subcortical white matter and in the centrum semiovale, and 3) numerous ectopic neurons, often containing tau-immunopositive neurofibrillary tangles, in the white maner of the frontal and temporal lobes. A molecular genetic analysis of DNA extracted from brain tissue of the proband revealed a S169L mutation in the Presenilin 1 (PSEN1) gene. The importance of this case lies in the presence of ectopic neurons in the white matter, early-onset seizures, and a PSEN1 mutation. We hypothesize that the PSEN1 mutation may have a causal relationship with an abnormality in neuronal development.

Amyloid angiopathy and variability in amyloid beta deposition is determined by mutation position in presenilin-1-linked Alzheimer's disease

The presenilins (PSs) are components of large molecular complexes that contain beta-catenin and function as gamma-secretase. We report here a striking correlation between amyloid angiopathy and the location of mutation in PS-1 linked Alzheimer's disease. The amount of amyloid beta protein, Abeta(42(43)), but not Abeta(40,) deposited in the frontal cortex of the brain is increased in 54 cases of early-onset familial Alzheimer's disease, encompassing 25 mutations in the presenilin-1 (PS-1) gene, compared to sporadic Alzheimer's disease. The amount of Abeta(40) in PS-1 Alzheimer's disease varied according to the copy number of epsilon4 alleles of the Apolipoprotein E gene. Although the amounts of Abeta(40) and Abeta(42(43)) deposited did not correlate with the genetic location of the mutation in a strict linear sense, the histological profile did so vary. Cases with mutations between codon 1 and 200 showed, in frontal cortex, many diffuse plaques, few cored plaques, and mild or moderate amyloid angiopathy. Cases with mutations occurring after codon 200 also showed many diffuse plaques, but the number and size of cored plaques were increased (even when epsilon4 allele was not present) and these were often clustered around blood vessels severely affected by amyloid angiopathy. Similarly, diverging histological profiles, mainly according to the degree of amyloid angiopathy, were seen in the cerebellum. Mutations in the PS-1 gene may therefore alter the topology of the PS-1 protein so as to favor Abeta formation and deposition, generally, but also to facilitate amyloid angiopathy particularly in cases in which the mutation lies beyond codon 200. Finally we report that the amount of Abeta(42(43)) deposited in the brain correlated with the amount of this produced in culture by cells bearing the equivalent mutations.

Phonological and articulatory impairment in Alzheimer's disease: a case series

We demonstrate that phonological and articulatory impairments may occur at presentation or early in the course of Alzheimer's disease, contrary to claims that these aspects of language production are relatively preserved until the final stages of this disease. Six patients with pathologically confirmed Alzheimer's disease (AD) and four patients with clinically diagnosed dementia of the Alzheimer's type (DAT) presented with one of five different clinical profiles: nonfluent progressive aphasia, mixed progressive aphasia, progressive aphasia diagnosed as DAT from neuropsychological assessment, initial amnestic syndrome with prominent phonological errors, and biparietal syndrome. Analysis of their conversational speech, single-word production, and performance of highly familiar series speech tasks such as counting revealed false start errors, phonological paraphasias, and/or articulatory difficulty. Neuropathological changes were located in left perisylvian regions consistent with speech and language impairment but atypical for Alzheimer's disease.

Missense mutations in the chromosome 14 familial Alzheimer's disease presenilin 1 gene

Mutations in the presenilin genes (PS-1 and PS-2) cause early onset autosomal dominant Alzheimer's disease (AD). Eight early-onset, autopsy-documented familial AD kindreds were screened for mutations in PS-1, and seven different mutations were identified. Three of these were new mutations (G209V, A426P, and E120D), two were previously reported mutations in new families, and three mutations were confirmed in previously published families. Two of these new mutations are found within predicted transmembrane domains (TMDs 4, 7, and 8). The A426P mutation is the most C-terminal PS-1 mutation identified to date.

Alzheimer's disease due to an intronic presenilin-1 (PSEN1 intron 4) mutation: A clinicopathological study

We describe 21 affected individuals from a kindred with early-onset autosomal dominant familial Alzheimer's disease caused by an intronic presenilin-1 mutation (in intron 4). Mean age at onset of symptoms was 37.4 years [95% confidence interval (CI): 36.6-38.2 years], mean age at death was 44.7 years (95% CI: 43.1-46.3 years) and mean duration of illness was 7.3 years (95% CI: 5.9-8.7 years). Myoclonus and seizures were prominent features of this pedigree. In the four cases for whom neuropsychometric data were available, verbal memory impairment preceded visual memory deficits; naming was relatively preserved until late in the disease. One of these four cases underwent serial volumetric MRI scans demonstrating in vivo brain tissue loss of 3.9% (38.9 ml, annualized rate of atrophy: 1. 7%) over 22 months of follow-up. The four individuals who had necropsies demonstrated the neuropathological hallmarks of Alzheimer's disease. Apolipoprotein E (APOE) status was assessed in five individuals: the case with the youngest age at onset at 33 years of age was found to be homozygous epsilon4/epsilon4, > 1 SD below the mean age of onset for those of known APOE genotype (36.4 +/- 2.3 years, mean +/- SD), and > 2 SDs below the mean age of onset for the pedigree as a whole (37.4 +/- 1.7 years, mean +/- SD). APOE genotype may therefore modulate age at onset in this pedigree.

Behavioral disturbances without amyloid deposits in mice overexpressing human amyloid precursor protein with Flemish (A692G) or Dutch (E693Q) mutation

The contribution of mutations in the amyloid precursor protein (APP) gene known as Flemish (APP/A692G) and Dutch (APP/E693Q) to the pathogenesis of Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis of the Dutch type, respectively, was studied in transgenic mice that overexpress the mutant APP in brain. These transgenic mice showed the same early behavioral disturbances and defects and increased premature death as the APP/London (APP V717I), APP/Swedish (K670N, M671L), and other APP transgenic mice described previously. Pathological changes included intense glial reaction, extensive microspongiosis in the white matter, and apoptotic neurons in select areas of the brain, while amyloid deposits were absent, even in mice over 18 months of age. This contrasts with extensive amyloid deposition in APP/London transgenic mice and less pronounced amyloid deposition in APP/Swedish transgenic mice generated identically. It demonstrated, however, that the behavioral deficiencies and the pathological changes in brain resulting from an impaired neuronal function are caused directly by APP or its proteolytic derivative(s). These accelerate or impinge on the normal process of aging and amyloid deposits per se are not essential for this phenotype.

Familial influence on variation in age of onset and behavioural phenotype in Alzheimer's disease

BACKGROUND

Alzheimer's disease manifests considerable heterogeneity, the cause of which is unknown.

AIMS

To determine the familial (genotypic) influence on phenomenology (phenotype) in Alzheimer's disease.

METHOD

Affected sibling pairs with Alzheimer's disease were assessed for a range of cognitive and non-cognitive symptoms. Resemblance for phenotypic characteristics was estimated using intraclass correlations for continuous traits and by pairwise concordance for dichotomous traits. The relationship between age of onset and APOE genotype was examined using linear regression analysis.

RESULTS

Significant familial effects on age of onset (intraclass correlation 0.41) and mood state (intraclass correlation 0.26), and a relatively high pairwise concordance for agitation (excess concordance 0.1) were found. The APOE locus was found to account for 4% of the variance in age of onset.

CONCLUSIONS

Substantial familial influence on age of onset, depression and agitation suggests that genotype does influence phenotype in Alzheimer's disease. Establishing the molecular basis for this phenotypic variation may prove relevant to other neuropsychiatric disorders.

Recent advances in the genetics of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that is the most common cause of dementia in the elderly. It is a clinical-pathologic entity characterized by progressive dementia associated with the neuropathologic hallmarks of Abeta amyloid plaques, neurofibrillary tangles (NFTs), neuronal loss, and amyloid angiopathy. Three "causative" AD genes (i.e., genes in which a mutation is sufficient to result in clinical AD) for early-onset familial Alzheimer's disease (FAD) and one "susceptibility" gene that affects risk and age of onset of AD in familial and sporadic late-onset AD have been identified. The three causative genes are the amyloid precursor protein (APP gene) on chromosome 21, the presenilin-1 gene on chromosome 14, and the presenilin-2 gene on chromosome 1. The susceptibility gene is the apolipoprotein E (APOE) gene on chromosome 19. Investigations of the normal and aberrant function of these genes will provide insights into the mechanisms underlying AD and will suggest new strategies for therapeutic intervention.

The impact of Alzheimer disease genetics on expert and advanced gerontological nursing practice

Alzheimer disease (AD), a progressive neurodegenerative disorder, is the most common cause of dementia in the United States, affecting as many as 4 million people. Extensive research is under way to identify environmental and genetic risk factors for this complex disease. Currently, four genes are associated with an increased risk for AD: the amyloid precursor protein gene on chromosome 21, the Presenilin I gene on chromosome 14, the Presenilin II gene on chromosome 1, and the apolipoprotein E gene on chromosome 19. Expert and advanced practice gerontological nurses are faced with new challenges as a result of these gene discoveries. Gerontological nurses should assess for relevant environmental and genetic risk factors; obtain comprehensive family health histories recorded as pedigrees; integrate genetic information into diagnosis, intervention, and evaluation strategies; initiate and coordinate referrals to genetic specialists; and provide ongoing emotional and decision-making support for patients and families experiencing AD.

Transgenic mice expressing an alpha-secretion mutant of the amyloid precursor protein in the brain develop a progressive CNS disorder

Expression of alpha-secretion mutant APP/RK in mouse brain results in a progressive disorganization of the central nervous system, exemplified by behavioral deficits, premature death and neuropathology. Here we report on the progressive nature of this CNS disorder as indicated by the age dependency of the neophobic reaction in the open-field test. The earlier reported NMDA hypo-sensitivity in the transgenic APP/RK mice is likely to represent a subtle functional disturbance, since no changes in NMDA receptor density or distribution could be detected. None of the typical neuropathological hallmarks of Alzheimer's Disease, i.e. amyloid deposits and neurofibrillary tangles are detected in the brain of these transgenic mice. Nevertheless, the progressive CNS disorder elicited in the transgenic APP/RK mice recapitulates certain features and symptoms of patients with Alzheimer's disease as discussed.

Chromosome 14 familial Alzheimer's disease: the clinical and neuropathological characteristics of a family with a leucine-->serine (L250S) substitution at codon 250 of the presenilin 1 gene

BACKGROUND

Seven affected members are described from a kindred with autosomal dominant familial Alzheimer's disease associated with a novel mutation in the presenilin 1 (PS1) gene on chromosome 14 that results in a leucine to serine substitution at codon 250 (L250S).

METHOD

Clinical information on the pedigree was collected directly from family members including affected members and their carers and also from hospital records.

RESULTS

Detailed clinical information was available on five members. All had an early age at onset with a median age of 52 (95% confidence interval (95% CI) 49.4-54.9). Age at onset varied between 49 and 56 years, with duration of illness varying between six years and 15 years. Myoclonus, depression, and psychosis were features of this pedigree; seizures were not reported.

CONCLUSIONS

PS1 L250S familial Alzheimer's disease is an early onset form of Alzheimer's disease with clinical features similar to other reported familial Alzheimer's disease pedigrees, except that seizures were absent.

Neurons and extracellular neurofibrillary tangles in the hippocampal subdivisions in early-onset familial Alzheimer's disease: a case study

We have investigated morphometrically unaffected neurons, intracellular neurofibrillary tangles (I-NFT) and extracellular neurofibrillary tangles (E-NFT) in eight subdivisions of the hippocampal cortex in two cases of early-onset familial Alzheimer's disease (FAD) and six cases of early-onset sporadic Alzheimer's disease (SAD). The hippocampal subdivisions examined included: CA4, CA3, CA2, CA1, prosubiculum, subiculum and presubiculum (PRE), parasubiculum (PARA) and entorhinal cortex (ENT). CA3, CA2 and CA1 in the FAD cases showed more severe neuronal loss and much greater E-NFT formation than in the SAD cases, while ENT in both the FAD cases showed less neuronal loss and less E-NFT formation. These data suggest that the cornu ammonis is affected more severely than the ENT in the FAD cases. These observations indicate that hippocampal pathology in the FAD cases is qualitatively as well as quantitatively different from that in sporadic cases. These results provide further evidence for pathological heterogeneity in AD, although the number of FAD cases examined is very small.

Cerebellar pathology in sporadic and familial Alzheimer's disease including APP 717 (Val-->Ile) mutation cases: a morphometric investigation

Familial Alzheimer's disease (FAD) tends to present with more prominent neurological symptoms including cerebellar signs than sporadic Alzheimer's disease (SAD). In order to elucidate the pathological differences in the cerebellum, which may be associated with the cerebellar symptoms, we have investigated morphometrically beta-amyloid deposits, atrocytosis, Purkinje cells and dentate neurons in the cerebellum of 10 FAD patients including two cases with the beta-amyloid precursor protein (APP) gene mutation (APP717 Val-->Ile), 10 SAD patients and 10 non-demented age-matched controls. The regions examined included the molecular, Purkinje cell and granular cell layers, the cerebellar white matter and the dentate nucleus. Purkinje cell density in FAD was significantly lower than in SAD. There were no significant differences in the density of dentate neurons among the three groups. The density of astrocytes in FAD was significantly greater than that in SAD in the granular cell and Purkinje cell layers and in the white matter. There were no significant differences in the amount and subtypes of beta-amyloid deposits (extracellular, vascular and perivascular) between FAD and SAD in all the regions investigated. In two cases with the APP mutation, both Purkinje cell loss and beta-amyloid deposition in the cerebellum were greater than the mean for FAD and SAD cases. Astrocytosis in the mutation cases was not greater than the mean for FAD cases except for the dentate nucleus in one case. Extracellular beta-amyloid deposits were not seen in any of the control cases although amyloid angiopathy was observed in one case. This study demonstrates for the first time that Purkinje cell loss and reactive astrocytosis of the cerebellum in FAD are more severe than in SAD, but that beta-amyloid deposition in the cerebellum in both FAD and SAD are similar. The more prominent neurological signs observed in FAD may be explained by more severe neurodegeneration than are found in sporadic cases.

Presenilin-1 protein expression in familial and sporadic Alzheimer's disease

Mutations of the presenilin PS1 and PS2 genes are closely linked to aggressive forms of early-onset (< 60 years) familial Alzheimer's disease. A highly specific monoclonal antibody was developed to identify and characterize the native PS1 protein. Western blot analyses revealed a predominant 32-kd immunoreactive polypeptide in a variety of samples, including PC12 cells transfected with human PS1 complementary DNA, brain biopsy specimens from demented patients, and postmortem samples of frontal neocortex from early-onset familial Alzheimer's disease cases (PS1 and PS2), late-onset sporadic Alzheimer's disease cases, and cases of other degenerative disorders. This truncated polypeptide contains the N-terminus of PS1 and appeared unchanged across cases. In 2 early-onset cases linked to missense mutations in the PS1 gene, a PS1 immunoreactive protein (approximately 49 kd) accumulated in the frontal cortex. This protein was similar in size to full-length PS1 protein present in transfected cells overexpressing PS1 complementary DNA, and in lymphocytes from an affected individual with a deletion of exon 9 of the PS1 gene, suggesting that mutations of the PS1 gene peturb the endoproteolytic processing of the protein. Immunohistochemical studies of control brains revealed that PS1 is expressed primarily in neurons, with the protein localized in the soma and dendritic processes. In contrast, PS1 showed striking localization to the neuropathology in early-onset familial Alzheimer's disease and sporadic Alzheimers' disease cases. PS1 immunoreactivity was present in the neuritic component of senile plaques as well as in neurofibrillary tangles. Localization of PS1 immunoreactivity in familial and sporadic Alzheimer's disease suggests that genetically heterogeneous forms of the disease share a common pathophysiology involving PS1 protein.

Clinical and molecular analysis of neurodegenerative diseases

Clinical and molecular analyses of neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and spinocerebellar ataxia type 1 (SCA1) were performed. In the present study, a Japanese family of AD with an Ala285Val substitution in exon 8 of the presenilin-1 (PS-1) gene was found. This family was characterized by relatively late onset (mean age at 50 years) in familial AD with PS-1 gene mutation and by absence of myoclonus, seizure or paratonia. Magnetic resonance image (MRI) study showed marked linear signal abnormalities in white matter of parietoocctipital lobes, suggesting a presence of cortical amyloid angiopathy of the patient with PS-1 gene mutation. Clinical characteristics of familial amyotrophic lateral sclerosis (FALS) with four different missense point mutations in exons 2, 4, and 5 of the Cu/Zn superoxide dismutase (SOD) gene were reported. Although features of progressive neurogenic muscular atrophy was common in patients of these families, patients of each family showed characteristic clinical features. Although lower motor sign was evident in all cases, hyperreflexia varied from 0 to 100% among patients with the different mutations, and Babinski sign was not observed in any cases. Bulbar palsy was frequent with a mutation, but not present with another mutation. SOD activity of red blood cells was generally reduced with minor variations. CAG trinucleotide repeat expansion was analyzed in 25 families with hereditary ataxia of Menzel type in the northeast of Japan. Twenty of 38 patients in 12 families had expanded allele for spinocerebellar ataxia type 1 (SCA1). Study of the number of CAG repeats in various tissues showed no differences in the repeat length in lymphocytes, muscle or brain; sperm, however, showed an obvious expansion. This may be a clue to a possible mechanism for the molecular basis of paternal anticipation of the disease. These results suggest that clinical features of some familial cases of neurodegenerative diseases such as AD, ALS, and SCA1 are well correlated with their genetic mutations.

Enhanced production and oligomerization of the 42-residue amyloid beta-protein by Chinese hamster ovary cells stably expressing mutant presenilins

Mutations in the presenilin 1 (PS1) and presenilin 2 (PS2) genes cause the most common and aggressive form of early onset familial Alzheimer's disease. To elucidate their pathogenic mechanism, wild-type (wt) or mutant (M146L, C410Y) PS1 and wt or mutant (M239V) PS2 genes were stably transfected into Chinese hamster ovary cells that overexpress the beta-amyloid precursor protein (APP). The identity of the 43-45-kDa PS1 holoproteins was confirmed by N-terminal radiosequencing. PS1 was rapidly processed (t1/2 = 40 min) in the endoplasmic reticulum into stable fragments. Wild-type and mutant PS2 holoproteins exhibited similar half lives (1.5 h); however, their endoproteolytic fragments showed both mutation-specific and cell type-specific differences. Mutant PS1 or PS2 consistently induced a 1.4-2.5-fold increase (p < 0.001) in the relative production of the highly amyloidogenic 42-residue form of amyloid beta-protein (Abeta42) as determined by quantitative immunoprecipitation and by enzyme-linked immunosorbent assay. In mutant PS1 and PS2 cell lines with high increases in Abeta42/Abetatotal ratios, spontaneous formation of low molecular weight oligomers of Abeta42 was observed in media, suggesting enhanced Abeta aggregation from the elevation of Abeta42. We conclude that mutant PS1 and PS2 proteins enhance the proteolysis of beta-amyloid precursor protein by the gamma-secretase cleaving at Abeta residue 42, thereby promoting amyloidogenesis.

Autosomal dominant early onset dementia and leukoencephalopathy in a Japanese family: clinical, neuroimaging and genetic studies

We report here the results of clinical, neuroimaging and genetic studies of autosomal dominant dementia and leukoencephalopathy in a Japanese family. Twenty-two individuals in this family were examined clinically (17 living, 5 deceased), neuroradiologically and genetically (16 of 17 living members). Ten (5 deceased) of 22 individuals had early onset dementia (age of onset: 45.2 +/- 12.1 years on average) and four of them had multiple white matter lesions and brain atrophy on brain MRI without history of brain ischemic attack. Another four individuals had abnormal white matter lesions on brain MRI without dementia. Linkage studies for chromosome 1q31-42, 14q24.3 and 21q21 responsible for Alzheimer's disease, chromosome 19p13.1-13.2 for cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and chromosome 3 for familial non-specific dementia suggested no specific haplotypes cosegregated with the disease. Apo E genotypes were E2/2 and E2/3 in this family. Clinical, neuroimaging and genetic studies revealed that the disease in this family was distinguished from known familial dementia. This is the first report of a large Japanese family with autosomal dominant early onset dementia and leukoencephalopathy.

Tau phosphorylation in cells transfected with wild-type or an Alzheimer's disease mutant Presenilin 1

We have studied the effect of overexpressing either wild-type or an Alzheimer's disease mutant Presenilin 1 (PS1) on tau phosphorylation in transfected Chinese hamster ovary (CHO) and COS cells. Tau transfected into these cells is predominantly non-phosphorylated at many PHF-tau sites but co-transfection with the tau kinase glycogen synthase kinase-3 beta (GSK-3 beta) induces phosphorylation that generates epitopes for several phosphorylation-dependent antibodies. Co-transfection of tau with either wild-type or mutant PS1 did not alter tau phosphorylation as detected by five different antibodies. Likewise, co-transfection of the PS1s did not influence GSK-3 beta-mediated tau phosphorylation. The implications of these results for the pathogenesis of Alzheimer's disease are discussed.

Wide range in age of onset for chromosome 1--related familial Alzheimer's disease

Mutations in three different genes on chromosomes 1, 14, and 21 cause autosomal dominant forms of familial Alzheimer's disease (FAD). Most result in an early-onset phenotype. However, several kindreds of Volga German ancestry have the same chromosome 1 gene mutation and demonstrate a relatively older mean age of onset and include individuals with late age of onset. In these families, the mean age of onset is 54.9 +/- 8.4 years (range, 40-75 years), mean age at death is 65.9 +/- 10.2 years (range, 43-88 years), and mean disease duration is 11.3 +/- 4.6 years (range, 5-23 years). This contrasts with a group of 7 families with chromosome 14 mutations in which the mean age of onset is 44.8 +/- 4.8 years (range, 30-55 years), mean age at death is 52.6 +/- 5.7 years (range, 39-65 years), and mean disease duration is 7.6 +/- 3.2 years (range, 2-17 years). (All means are significantly different in the 2 groups of families, p < 0.005.) In the chromosome 1 families, 7 persons (16%) had an age of onset at or older than 65 years and 22 (54%) survived to age 65 or older versus none in the chromosome 14 families. An example of probable nonpenetrance of disease at age 89 was also found in a chromosome 1 kindred. It is concluded that, unlike the chromosome 14 gene, mutations in the chromosome 1 FAD gene may result in individuals with a late age of onset overlapping with the more common sporadic form of the disease occurring in the general population. In light of the great variability in age of onset in persons with identical mutations, study of the genetic and environmental factors contributing to delayed onset of disease in chromosomal 1 FAD kindreds will be an important area for further investigation. Apolipoprotein E genotype may be one such factor that plays a partial role in this variability.

The E280A presenilin 1 Alzheimer mutation produces increased A beta 42 deposition and severe cerebellar pathology

Missense mutations in the presenilin 1 (PS1) gene cause the most common form of dominant early-onset familial Alzheimer's disease (FAD) and are associated with increased levels of amyloid beta-peptides (A beta) ending at residue 42 (A beta 42) in plasma and skin fibroblast media of gene carriers. A beta 42 aggregates readily and appears to provide a nidus for the subsequent aggregation of A beta 40 (ref. 4), resulting in the formation of innumerable neuritic plaques. To obtain in vivo information about how PS1 mutations cause AD pathology at such early ages, we characterized the neuropathological phenotype of four PS1-FAD patients from a large Colombian kindred bearing the codon 280 Glu to Ala substitution (Glu280Ala) PS1 mutation. Using antibodies specific to the alternative carboxy-termini of A beta, we detected massive deposition of A beta 42, the earliest and predominant form of plaque A beta to occur in AD (ref. 6-8), in many brain regions. Computer-assisted quantification revealed a significant increase in A beta 42, but not A beta 40, burden in the brains from 4 PS1-FAD patients compared with those from 12 sporadic AD patients. Severe cerebellar pathology included numerous A beta 42-reactive plaques, many bearing dystrophic neurites and reactive glia. Our results in brain tissue are consistent with recent biochemical evidence of increased A beta 42 levels in PS1-FAD patients and strongly suggest that mutant PS1 proteins alter the proteolytic processing of the beta-amyloid precursor protein at the C-terminus of A beta to favor deposition of A beta 42.

Purkinje cell loss and astrocytosis in the cerebellum in familial and sporadic Alzheimer's disease

In order to elucidate further the pathological differences between familial Alzheimer's disease (FAD) and sporadic Alzheimer's disease (SAD), Purkinje cells and astrocytosis in the cerebellum of 10 FAD patients including two cases with the beta-amyloid precursor protein (APP) gene mutation in codon 717 (APP717 Val-->Ile), 10 SAD patients and 10 non-demented, age-matched controls were morphometrically investigated using immunohistochemistry. The regions examined included the molecular, Purkinje cell and granular cell layers, and the cerebellar white matter. This is the first report of a significantly decreased Purkinje cell density in FAD when compared to SAD. The density in SAD was also significantly decreased when compared to controls. In addition, the astrocyte density in FAD was significantly greater than that of SAD in the Purkinje cell layer, granular cell layer, and white matter. The density in SAD was also greater than that in controls, but not significantly in the granular cell layer and white matter. In the cases with the APP717 (Val-->Ile) mutation, Purkinje cell loss in the cerebellum was greater than the mean for FAD and SAD cases, while the astrocyte density was lower than the mean of all FAD cases, but higher than the mean of SAD cases. This study demonstrates that Purkinje cell loss and astrocytosis in FAD in the cerebellum are greater than in SAD, indicating that the cerebellum is more affected in FAD than in SAD.