Are the associations between Alzheimer's disease and polymorphisms in the apolipoprotein E and the apolipoprotein CII genes due to linkage disequilibrium?

Apolipoprotein E: Emerging Story in the Pathogenesis of Alzheimer's Disease

Apolipoprotein E (apoE) is implicated in the pathogenesis of Alzheimer's disease. One of the three com mon apoE alleles, apoE4, behaves as an autosomal codominant trait in the majority of late-onset and sporadic Alzheimer's disease, with homozygosity for this allele virtually sufficient to cause disease by the age of 80. In contrast, the apoE2 and apoE3 alleles decrease the probability of disease and increase the age of onset, with the protective effect of apoE2 greater than apoE3. Thus, the inherited alleles of apoE determine, in part, the risk of developing Alzheimer's disease and determine the rate of disease progres sion. Isoform-specific interactions of apoE with other molecules are therefore critical in this disease. ApoE is found in populations of neurons, some of which contain abnormal neurofibrillary tangles assembled from the protein tau. In healthy neurons, tau helps assemble and stabilize microtubules, but in Alzheimer's disease, it forms paired helical filaments of the neurofibrillary tangle. ApoE3 avidly binds tau in vitro, whereas apoE4 does not. Isoform-specific interactions of apoE with tau and other microtubule-associated proteins could contribute to the mechanism of Alzheimer's disease. Uncovering the roles of apoE in the brain, both in health and in disease, will be an exciting area for neuroscience. The Neuroscientist 1:298- 306, 1995

A randomized double-blind trial of the effects of hormone therapy on delayed verbal recall in older women

We examined whether estradiol and norethindrone hormone therapy (HT) prevented decline in delayed verbal recall in older women with normal to mildly impaired memory functioning. This was a 2-year, randomized, double-blind, placebo-controlled trial of 142 women aged 61-87, randomly assigned to receive 1 mg 17-beta estradiol daily and 0.35 mg norethindrone 3 days/week or daily placebo for 2 years. The primary outcome was short-delay verbal recall of the California Verbal Learning Test (CVLT). To look for differences in response to HT by baseline short-delay recall, we examined the primary outcome in participants grouped according to whether their baseline scores were below average for the age group or greater than or equal to this score and according to whether they met criteria for Mild Cognitive Impairment (MCI) or not. 133 women completed 1 year of the trial and 128 completed 2 years. Prespecified covariates in all repeated measures analyses of covariance (RANCOVA) included age, education, APOE epsilon4, and prior HT use. RANCOVA showed no overall significant treatment effects at year 1 or year 2. After testing for an interaction, which was significant (p=0.02), we found that women in the HT group who scored at or above the average showed significantly less decline than the placebo group in short-delay verbal recall after 1 year, p=0.007 and 2 years, p=0.01. No treatment effects were found in women below the average in either year. When grouped according to whether the participant met criteria for MCI, the interaction between treatment group and MCI subgroup was not significant. These results suggest that benefits of estrogen exposure may be limited to those with average to above average scores on the delayed verbal recall. HT dose and formulation may have contributed to these beneficial outcomes. Replication is warranted before recommendations can be made in the clinical setting.

APOE distribution in world populations with new data from India and the UK

BACKGROUND

The APOE gene and its protein product is associated with a number of plasma proteins like very-low density lipoprotein (VLDL), high density lipoprotein (HDL) chylomicrons, chylomicron remnants, and plays a crucial role in lipid metabolism. The APOE gene is polymorphic and common alleles (*E2, *E3 and *E4) have been associated with a number of common and complex diseases in different populations. Due to their crucial role in metabolism and clinical significance, it is imperative that allelic variation in different populations is analysed to evaluate the usage of APOE in an evolutionary and clinical context.

AIM

We report allelic variation at the APOE locus in three European and four Indian populations and evaluate global patterns of genetic variation at this locus. The large, intricate and unexpected heterogeneity of this locus in its global perspective may have insightful consequences, which we have explored in this paper.

SUBJECT AND METHODS

Apolipoprotein E genotypes were determined in four population groups (Punjabi Sikhs, Punjabi Hindus, Maria Gonds and Koch, total individuals = 497) of India and three regionally sub-divided British populations (Nottinghamshire, East Midlands and West Midlands, total individuals = 621). The extent and distribution of APOE allele frequencies were compared with 292 populations of the world using a variety of multivariate methods.

RESULTS

Three alleles, APOE*E2, APOE*E3 and APOE*E4, were observed with contrasting variation, although *E4 was absent in the tribal population of Koch. Higher heterozygosities (>43%) in British populations reflected their greater genetic diversity at this locus. The overall pattern of allelic diversity among these populations is comparable to many European and Indian populations. At a global level, higher frequencies of the *E2 allele were observed in Africa and Oceania (0.099 +/- 0.083 and 0.111 +/- 0.052, respectively). Similarly, *E4 allele averages were higher in Oceania (0.221 +/- 0.149) and Africa (0.209 +/- 0.090), while Indian and Asian populations showed the highest frequencies of *E3 allele. The coefficient of gene differentiation was found to be highest in South America (9.6%), although the highest genetic diversity was observed in Oceania (48.7%) and Africa (46.3%). APOE*E2 revealed a statistically significant decreasing cline towards the north in Asia (r = -0.407, d.f. = 70, p < 0.05), which is not compatible with the coronary heart disease statistics in this continent. APOE*E4 showed a significant increasing cline in North European populations. Spatial autocorrelation analysis shows that the variation at this locus is influenced by 'isolation by distance' with a strong positive correlation for lower distances up to 1313 km.

CONCLUSION

Overall APOE allelic variation in UK and Indian populations is comparable to previous studies but in tribal populations *E4 allele frequency was very low or absent. At a global level allelic variation shows that geography, isolation by distance, genetic drift and possibly pre-historical selection are responsible for shaping the spectrum of genetic variation at the APOE gene. Overall, APOE is a good anthropogenetic and clinical diagnostic marker.

Non-apolipoprotein E and apolipoprotein E genetics of sporadic Alzheimer's disease

The genetic epidemiology of sporadic Alzheimer's disease (SAD) remains a very active area of research,making it one of the most prolifically published areas in medicine and biology. Numerous putative candidate genes have been proposed. However, with the exception of apolipoprotein E (APOE), the only confirmed genetic risk factor for SAD, all the other data appear to be not consistent. Nevertheless, the genetic risk for SAD attributable to the APOE gene in the general population is 20-0%, providing a strong evidence for the existence of additional genetic risk factors. The first part of the present article was dedicated to non-APOE genetics of SAD, reviewing chromosomes-by-chromosomes the available data concerning the major candidate genes. The second part of this article focused on some recently discovered aspects of the APOE polymorphism and their implications for SAD. An attempt to identify the future directions for non-APOE genetic research in SAD was also discussed.

Conversion to dementia among two groups with cognitive impairment. A preliminary report

OBJECTIVE

To determine the conversion rates to dementia in patients diagnosed with mild cognitive impairment (MCI) thought to be caused by incipient Alzheimer's disease (MCI-AD) or with MCI with features of vascular disease (MCI-Vas).

METHODS

On the basis of patient history, neurocognitive, neurological and MRI evaluation, 99 patients were diagnosed with MCI-AD and 35 with MCI-Vas. Conversion to dementia over an average of a 2.4 +/- 1.8-year period was determined.

RESULTS

Over the follow-up period, 44% converted to dementia, 51.5% remained classified as MCI, and 4.5% were reclassified as cognitively normal. The conversion rate to dementia was significantly faster at 3 years for the MCI-AD (50.5%) than for the MCI-Vas group (25.7%). The neuropsychological test found to best differentiate converters from non-converters was the Fuld-OME, a measure of learning and recall. Age, education, gender or APOE epsilon4 allele frequency did not differentiate converters from non-converters.

CONCLUSIONS

MCI-AD and MCI-Vas are clinically meaningful subtypes of MCI that may convert to dementia at different rates. Prospective studies on larger subsets of MCI patients are required to confirm these findings.

A cross-sectional study of lipids and ApoC levels in Alzheimer's patients with and without cardiovascular disease

BACKGROUND

There is increasing evidence supporting the role of atherogenic phenomena in Alzheimer's disease (AD). The possible significance of specific plasma lipid levels in the pathogenesis of AD remains controversial. While lipids such as cholesterol or chaperons such as apolipoprotein (Apo) E2 to ApoE4 have been assessed in AD, ApoC2 and ApoC3 have not been studied before. The present study investigated possible differences in levels of these lipids in AD patients, with or without cardiovascular diseases or risk factors.

METHODS

This is a cross-sectional study. The medical charts of patients diagnosed with probable AD were screened for the presence of cardiovascular disease and cardiovascular risk factors. Included in the study were 105 AD patients: 53 with cardiovascular risk factors (AD(+CVD)) and 52 without risk factors (AD(-CVD)). Blood samples were analyzed for lipoproteins, ApoC2, and ApoC3. We used t tests, chi-square tests, and regression analyses to identify significant differences and to compare the relationships of variables among the groups.

RESULTS

ApoC2 levels (3.5 +/- 0.3 and 3.4 +/- 0.4 mg/dl, respectively), ApoC3 (13.7 +/- 0.9 and 14.7 +/- 1.1 mg/dl, respectively), and high-density lipoprotein (HDL)/non-HDL ApoC3 ratios (1.6 +/- 0.2 and 1.3 +/- 0.2, respectively) were similar for the AD patients with and without cardiovascular risk factors. Levels of total cholesterol, triglycerides, low-density lipoproteins (LDL), very LDLs, and HDLs were similar in the two groups. A substantial proportion of both AD(+CVD) and AD(-CVD) patients showed high levels of total cholesterol and LDL, as well as low levels of HDL, ApoC2, and ApoC3, compared to normative values. Surprisingly, patients treated by cognitive enhancers showed significantly higher cholesterol ( p =.002) and triglyceride ( p =.015) levels, independent of age, gender, and cognitive level.

CONCLUSIONS

There was no difference between AD patients, either with or without cardiovascular diseases or risk factors, with respect to plasma lipid profile, including ApoC2 and ApoC3. This could indicate that lipid metabolism may play a role in AD, whether with or without cardiovascular risk factors. The higher levels of some lipids, observed in a subset of patients treated by cognitive enhancers, deserves further investigation.

Recent origin and spread of a common Lithuanian mutation, G197del LDLR, causing familial hypercholesterolemia: positive selection is not always necessary to account for disease incidence among Ashkenazi Jews

G197del is the most prevalent LDL receptor (LDLR) mutation causing familial hypercholesterolemia (FH) in Ashkenazi Jew (AJ) individuals. The purpose of this study was to determine the origin, age, and population distribution of G197del, as well as to explore environmental and genetic effects on disease expression. Index cases from Israel (n=46), South Africa (n=24), Russia (n=7), The Netherlands (n=1), and the United States (n=1) were enlisted. All trace their ancestry to Lithuania. A highly conserved haplotype (D19S221:104-D19S865:208-D19S413:74) was identified in G197del chromosomes, suggesting the occurrence of a common founder. When two methods were used for analysis of linkage disequilibrium (LD) between flanking polymorphic markers and the disease locus and for the study of the decay of LD over time, the estimated age of the deletion was found to be 20 +/- 7 generations (the 95% confidence interval is 15-26 generations), so that the most recent common ancestor of the mutation-bearing chromosomes would date to the 14th century. This corresponds with the founding of the Jewish community of Lithuania (1338 a.d.), as well as with the great demographic expansion of AJ individuals in eastern Europe, which followed this settlement. The penetrance of mutation-linked severe hypercholesterolemia is high (94% of heterozygotes have a baseline concentration of LDL cholesterol (LDL-C) that is >160 mg/dl), and no significant differences in the mean baseline lipid level of G197del carriers from different countries were found. Polymorphisms of apolipoprotein E and of scavenger-receptor class B type I were observed to have minor effects on the plasma lipid profile. With respect to determinative genetic influences on the biochemical phenotype, there is no evidence that could support the possibility of a selective evolutionary metabolic advantage. Therefore, the founder effect in a rapidly expanding population from a limited number of families remains a simple, parsimonious hypothesis explaining the spread of G197del-LDLR-linked FH in AJ individuals.

Relation of apolipoprotein E polymorphism to clinically diagnosed Alzheimer's disease in the Korean population

The gene for human apolipoprotein E (APOE) is found on the long arm of chromosome 19 (19q13.2) and exists in three common allelic forms, epsilon2, epsilon3, and epsilon4. The APOE epsilon4 allele is overrepresented in Alzheimer's disease (AD) and is accepted as a genetic risk factor. Some studies reported a protective effect of the APOE epsilon2 allele for AD. However, there are some ethnic variations in the proportion of different APOE alleles and their relationship to AD. We examine the distribution of APOE alleles from 30 AD patients and 158 controls in Korea. The control subjects were all cognitively intact unrelated Koreans. The frequencies of APOE alleles in AD patients were 18.3% (epsilon2), 58.3% (epsilon3), and 23.3% (epsilon4). The corresponding frequencies in controls were 13.3% (epsilon2), 72.5% (epsilon3), and 14.2% (epsilon4). The frequency of the APOE epsilon2 allele in AD patients was not significantly different from that in controls. When statistical analysis was conducted after the exclusion of the APOE epsilon2 allele, the frequency of the APOE epsilon4 allele in AD patients was significantly higher than that in controls (P < 0.05). These results support that the APOE epsilon4 allele plays a role as a risk factor for AD in Koreans and suggest that the APOE epsilon2 allele may not play a protective role in the development of AD in Koreans.

Brain atrophy in relapsing-remitting multiple sclerosis and secondary progressive multiple sclerosis: longitudinal quantitative analysis

PURPOSE

To determine annual rates of volumetric changes in the whole-brain parenchyma of patients with relapsing-remitting and secondary progressive multiple sclerosis (MS) and test the hypothesis that these changes correlate with clinical disability.

MATERIALS AND METHODS

A computer-assisted segmentation technique with thin-section magnetic resonance (MR) imaging was used in 36 patients with MS (27 relapsing-remitting, nine secondary progressive) and in 20 control subjects to quantify brain and cerebrospinal fluid volumes. To determine the degree of brain atrophy, the percentage brain parenchyma volume (PBV) relative to that of intracranial contents was calculated.

RESULTS

At the beginning of the study, the PBV was smaller in the MS group than in the control group (P = .007); brain parenchyma volumes were similar. The median rate of brain volume loss was 17.3 mL per year in patients with relapsing-remitting MS and 23.6 mL per year in those with secondary progressive MS. There was a negative correlation between brain atrophy and Expanded Disability Status Scale (EDSS) score in patients with secondary progressive MS (r = -0.69, P = .004) and no correlation in patients with relapsing-remitting MS. T2 lesion volume did not correlate with brain atrophy in either group.

CONCLUSION

The correlation between brain atrophy and EDSS score was better in patients with secondary progressive MS than in those with relapsing-remitting MS.

Apolipoprotein E phenotypes in healthy normal controls and demented subjects with Alzheimer's disease and vascular dementia in Mie Prefecture of Japan

In order to clarify the association between apolipoprotein E4 (ApoE4) and the pathogenesis of Alzheimer's disease (AD), we analyzed the distribution of the apolipoprotein E (ApoE) phenotypes and the frequency of the apo E alleles epsilon2, epsilon3, and epsilon4 in Japanese healthy controls (n = 1090, an average age of 51.2+/-12.6 years) and demented patients (n=103, mean age of 73.6+/-9.2 years). Demented subjects were divided into three subgroups: early-onset AD group (EOAD; n=25, mean age 63.0+/-6.2 years), late-onset AD group (LOAD; n=33, mean age 79.3+/-5.1 years), and vascular dementia group (VD; n=45, mean age 75.3+/-8.0 years). The apolipoprotein E phenotype was determined by isoelectric focusing and immunoblotting. There were no significant differences in the distribution of the apo E phenotypes by gender or age, and the estimated frequencies of epsilon2, epsilon3 and epsilon4 were 0.05, 0.86 and 0.09, respectively, in the normal controls. There was a significant difference in the distribution of the apo E phenotypes between LOAD and elderly controls aged more than 65 years (P<0.0001). The distribution of the apo E phenotypes in EOAD was the same as that in LOAD. The frequency of the epsilon4 allele was significantly higher in LOAD (0.35, P<0.0001) and EOAD (0.28, P<0.0001) than that in the control subjects (0.07), but not in VD (0.12, P=0.1630). The present findings suggest that ApoE4 is related with both EOAD and LOAD, but not with VD, and support the hypothesis that it is a genetic risk factor of AD.

Progressive multifocal leukoencephalopathy and human immunodeficiency virus-associated white matter lesions in AIDS: magnetization transfer MR imaging

PURPOSE

To determine the magnetization transfer features of progressive multifocal leukoencephalopathy (PML) and human immunodeficiency virus (HIV)-associated white matter lesions (WML) (hereafter, HIV-WML) on magnetic resonance (MR) images obtained in patients with acquired immunodeficiency syndrome (AIDS).

MATERIALS AND METHODS

Conventional MR imaging and magnetization transfer MR imaging were performed in 21 AIDS patients with 42 areas of white matter hyperintensity on MR images (13 patients had 25 PML lesions, eight patients had 17 WML). The magnetization transfer ratio was calculated for each lesion.

RESULTS

Compared with normal-appearing white matter (magnetization transfer ratio = 47.9%), both PML and HIV-WML showed reduced magnetization transfer ratio. The magnetization transfer ratio was significantly lower in PML lesions (magnetization transfer ratio = 26.1%) than in HIV-WML (magnetization transfer ratio = 38.0%, P < .0001), and there was no overlap in the magnetization transfer ratio between PML lesions and HIV-WML. The separation in magnetization transfer ratio between the two lesion types was valid for lesion as small as 0.5 cm2.

CONCLUSION

The larger reduction in magnetization transfer ratio for PML lesions is most likely due to demyelination, whereas the reduction in HIV-WML may be associated primarily with gliosis. PML lesions appear to cause strong reductions in magnetization transfer ratio early in the course of disease. Magnetization transfer MR imaging is a noninvasive tool that improves the differentiation between PML and HIV-WML in patients with AIDS.

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.

Genetics of complex human diseases: genome screening, association studies and fine mapping

Positional cloning has been applied successfully to many Mendelian disorders. Because of the public health significance, there is strong interest in mapping susceptibility genes for common disorders, such as asthma and allergy, that have a genetic component. Genome-wide screening has been very useful in detecting regions of the genome likely to contain susceptibility genes. There are multiple chromosomal regions implicated in asthma and now the difficult process of finding the genes and relevant mutations is underway. Two approaches that are being utilized are those of association studies in candidate genes, and haplotype sharing or identical by descent (IBD) mapping. Although these are useful approaches, it is important to realize the strengths and limitations of each. The level of significance needed for an initial study or a replication study should be considered in light of the prior evidence for studying a specific gene polymorphism. Haplotype-sharing approaches, although difficult to use in outbred heterogeneous populations, may provide important insight into fine mapping and gene localization.

Interfamilial and intrafamilial phenotypic heterogeneity in familial Alzheimer's disease

The features of Alzheimer's disease (AD) are very heterogenous, and some component of the variability of AD is likely to be related to genetic factors. To investigate this question, we evaluated 19 clinical neuropsychiatric and brain imaging features in 32 familial Alzheimer's disease (FAD) kindred, primarily of late onset. Within families, patients displayed a high degree of phenotypic heterogeneity (PH), which occurred irrespective of gender, ethnicity, or apolipoprotein E genotype. Overall, an equivalent amount of PH was observed in both the between- (37%) and within-family (31%) groups. However, for onset age and rate of decline between families, there was greater PH than within families (P = .002 and P = .01, respectively). A similar trend was found for severity of cortical atrophy (P = .05). These observations suggest a weak genetic influence, and possibly strong nongenetic influences, on the degree of phenotypic heterogeneity in late-onset FAD. In early-onset AD kindred, a much smaller degree of phenotypic heterogeneity may be expected within families, because genetic influences in phenotypic expression tend to be more prominent in early-onset cases.

Alzheimer's disease and apolipoprotein E genotype in Western Australia: an autopsy-verified series

OBJECTIVE

To determine the relationship between the apolipoprotein E epsilon 4 allele and autopsy-verified Alzheimer's disease (AD) in an Australian population.

DESIGN

Retrospective case-control study.

SETTING

Royal Perth Hospital, Perth, Western Australia (a tertiary referral hospital).

SUBJECTS

50 subjects with "definite" AD (according to the histological and clinical criteria of the Consortium to Establish a Registry for Alzheimer's Disease [CERAD]) and 30 control subjects who had died from a non-neurological disease were randomly selected from the hospital's neuropathology register.

OUTCOME MEASURES

Histological grading of brain sections stained with the modified Bielschowsky stain according to the criteria of CERAD; number (burden) of neuritic plaques; apolipoprotein E genotype (APOE).

RESULTS

Frequency of the epsilon 4 allele was significantly higher in the AD group (37%) than in the control group (2%) (chi 2 = 25.8; P < 0.00001). In the AD group, 50% of subjects were heterozygous for the epsilon 4 allele and 12% were homozygous, while in the control group one subject was heterozygous for the allele and none were homozygous. No association was seen between the epsilon 4 allele and neuritic plaque burden in the hippocampus, entorhinal cortex, middle frontal gyrus or inferior parietal lobule in subjects with AD.

CONCLUSIONS

Our findings confirm an association between the epsilon 4 allele and autopsy-verified AD. The epsilon 4 allele may be an important risk factor for susceptibility to AD in the general Australian population.

The clinical epidemiology of Alzheimer's disease

Alzheimer's disease is a more common and malignant illness than was appreciated just 2 decades ago. In addition to being a major cause of mortality, it is costly and uniquely distressing for patients and their families. All indications are that the problem will grow as elderly populations expand. Fatalism regarding AD is premature, however. Much has been learned about this disease in only a few years, and it is hoped that this rate of discovery can be maintained or even accelerated in the future.

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.

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.

A case-control study of apolipoprotein E genotypes in Alzheimer's disease associated with Down's syndrome. Dutch Study Group on Down's Syndrome and Ageing

The prevalence of clinical signs and neuropathological findings of Alzheimer's disease (AD) is high in Down's syndrome (DS). In the general population, the apolipoprotein E (ApoE) epsilon 4 isoform is an important risk for AD. We studied the allelic frequencies of ApoE in 26 DS cases fulfilling clinical diagnostic criteria for AD and in 26 DS controls matched for age, sex, and premorbid level of mental retardation. A meta-analysis of data available in the literature was used for comparison with allele frequencies in other AD and control populations. ApoE type 2, 3, or 4 allele frequencies were not significantly different in AD-DS cases and DS controls. The ApoE epsilon 4 frequency in DS cases with AD (0.14; CI, 0.06-0.26) was significantly lower than in any other AD population studied so far and it is within the range of nondemented controls from the general population. These findings suggest that ApoE epsilon 4 does not significantly affect the pathogenesis of AD in DS patients.

A germline substitution in the human MSH2 gene is associated with high-grade dysplasia and cancer in ulcerative colitis

BACKGROUND & AIMS

The DNA mismatch repair gene human MSH2 shows a germline mutation in certain family members with hereditary nonpolyposis colorectal cancer. There is an increased risk of colorectal cancer in patients with ulcerative colitis (UC) with extensive disease of > 8 years' duration; however, specific constitutional predisposing genetic abnormalities have not yet been identified.

METHODS

A germline human MSH2 abnormality was sought in patients with UC with high-grade dysplasia or carcinoma.

RESULTS

After direct sequencing of exon 13 and flanking regions of human MSH2, a germline T to C substitution was shown at the -6 intronic splice acceptor site of exon 13. This substitution was found in 14 of 53 patients with UC with high-grade dysplasia or carcinoma (26%) compared with 4 of 36 high-risk patients with UC without dysplasia or cancer (11%) (P < or = 0.04) and in 7 of 80 healthy adult blood donors (9%) (P < or = 0.003). The patients with UC who had the substitution were three times more likely to develop neoplasia than patients with UC who did not carry it.

CONCLUSIONS

An intronic splice-site substitution in the human MSH2 gene is present in the general population but may predispose to cancer in the setting of UC.

Apolipoprotein E and Alzheimer disease

Inheritance of specific apolipoprotein E (apoE) alleles determines, in large part, the risk and mean age of onset of late-onset familial and sporadic Alzheimer disease. The mechanism by which the apoE isoforms differentially contribute to disease expression is, however, unknown. Isoform-specific differences have been identified in the binding of apoE to the microtubule-associated protein tau, which forms the paired helical filament and neurofibrillary tangles, and to amyloid beta peptide, a major component of the neuritic plaque. These and other isoform-specific interactions of apoE give rise to testable hypotheses for the mechanism(s) of pathogenesis of Alzheimer disease. An unresolved issue of increasing importance is the relationship between the structural pathological lesions and the cellular pathogenesis responsible for the clinical disease phenotype, progressive dementia. The identification of apoE in the cytoplasm of human neurons and the characterization of isoform-specific binding of apoE to the microtubule-associated proteins tau and MAP-2 present the possibility that apoE may affect microtubule function in the Alzheimer brain.