The genetic association between Cathepsin D and Alzheimer's disease

Cathepsin D Polymorphism C224T in Childhood-Onset Neurodegenerative Disorders: No Impact for Childhood Dementia

Compromised lysosomal functioning has been identified as a major risk factor for neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Furthermore, the association between a defined cathepsin D ( CTSD ) polymorphism and a higher risk of sporadic Alzheimer's disease has been established for particular populations. Here, we analyzed 189 children with rare neurodegenerative disease for carrying the T-allele by polymerase chain reaction-restriction fragment length polymorphism. We found no statistical differences in genotype and allele frequencies between the neurodegenerative group and European descent participants of genetic studies using the Cochran-Armitage's trend test. In contrast to adult-onset neurodegenerative diseases, analysis of clinical datasets of children carrying the T-allele did not demonstrate differences to the general disease group.

Association study of cathepsin D gene polymorphism in Iranian patients with sporadic late-onset Alzheimer's disease

One of the most prevalent forms of dementia is Alzheimer's disease (AD). Complex inheritance and multifactorial patterns of late-onset AD (LOAD) along with its heterogeneity are due to the presence of different AD-predisposing genes with different influence on disease development among various populations. A key event in the pathogenesis of AD is the deposition of β-amyloid peptide, which is derived from the amyloid precursor protein by β- and γ-secretases. Cathepsin D (CTSD) is an acid protease with β- and γ-secretase-like features in vitro. An exonic C→T polymorphism at position 224 of the CTSD gene (rs: 17571) has been shown to be associated with the enzyme function of CTSD and with AD. Two studies in the German population reported a strong association of this polymorphism with an increased risk of developing AD, while other studies did not confirm this observation. We tested for this association in a case-control study in 100 Iranian sporadic LOAD patients based on diagnostic criteria of DSM-IV-TR and NINCDS-ADRDA and in 100 normal controls without any personal and family history of AD or other related dementias. Polymerase chain reaction-restriction fragment length polymorphism was set up to detect this polymorphism. Our study demonstrated that T-carrying genotype frequency in AD patients is significantly higher than in controls and there was a 2.5-fold increased risk for developing AD in the T-carrying genotype compared to C/C genotype (odds ratio = 2.5, p = 0.010). The odds ratio for subjects with the apolipoprotein E ε4 (APOE ε4) allele was 2.91 (p = 0.003) and carriers of the CTSD T and APOE ε4 alleles had a 6.25-fold increased risk of the disease (p = 0.0). Our results indicate that CTSD genotype is associated with the disease and a combination of the above risk factors significantly alters the risk for developing AD.

Human stefin B role in cell's response to misfolded proteins and autophagy

Alternative functions, apart from cathepsins inhibition, are being discovered for stefin B. Here, we investigate its role in vesicular trafficking and autophagy. Astrocytes isolated from stefin B knock-out (KO) mice exhibited an increased level of protein aggregates scattered throughout the cytoplasm. Addition of stefin B monomers or small oligomers to the cell medium reverted this phenotype, as imaged by confocal microscopy. To monitor the identity of proteins embedded within aggregates in wild type (wt) and KO cells, the insoluble cell lysate fractions were isolated and analyzed by mass spectrometry. Chaperones, tubulins, dyneins, and proteosomal components were detected in the insoluble fraction of wt cells but not in KO aggregates. In contrast, the insoluble fraction of KO cells exhibited increased levels of apolipoprotein E, fibronectin, clusterin, major prion protein, and serpins H1 and I2 and some proteins of lysosomal origin, such as cathepsin D and CD63, relative to wt astrocytes. Analysis of autophagy activity demonstrated that this pathway was less functional in KO astrocytes. In addition, synthetic dosage lethality (SDL) gene interactions analysis in Saccharomyces cerevisiae expressing human stefin B suggests a role in transport of vesicles and vacuoles These activities would contribute, directly or indirectly to completion of autophagy in wt astrocytes and would account for the accumulation of protein aggregates in KO cells, since autophagy is a key pathway for the clearance of intracellular protein aggregates.

Lack of association between cathepsin D C224T polymorphism and Alzheimer's disease risk: an update meta-analysis

BACKGROUND

Cathepsin D C224T polymorphism has been reported to associate with AD susceptibility. But the results were inconsistent. This study aimed to assess the relationship between C224T polymorphism and AD risk.

METHODS

The relevant studies were identified by searching PubMed, Embase, Web of Science, Google Scholar and Wan fang electronic databases updated on July 2013. The relationship between Cathepsin D C224T polymorphism and AD risk was evaluated by ORs and 95% CIs.

RESULTS

A total of 25 case-control studies including 5,602 cases and 11,049 controls were included in the meta-analysis. There was no association between C224T polymorphism and AD risk with all the studies were pooled in the meta-analysis (CT vs. CC: OR = 1.125, 95% CI = 0.974-1.299, P = 0.109; CT + TT vs. CC: OR = 1.136, 95% CI = 0.978-1.320, P = 0.094). Furthermore, when stratified by ethnicity, age of onset and APOEϵ4 status, significant association did not found in all subgroups.

CONCLUSION

The present meta-analysis suggested that the Cathepsin D C224T polymorphism was not associated with AD susceptibility.

The cathepsin D (224C/T) polymorphism confers an increased risk to develop Alzheimer's disease in men

The lysosomal protease cathepsin D is likely involved in beta-amyloidogenesis in Alzheimer's disease (AD). There is evidence for a single nucleotide polymorphism (rs17571) of the cathepsin D gene to be associated with increased AD risk. However, little is known about gender-specific differences. Therefore, we performed a genetic association study focusing on gender-specific differences in 434 participants (219 AD and 215 controls). Screening of the rs17571 shows a significantly higher proportion of T-allele carriers among male Alzheimer patients (28.5%) when compared with male controls (13.8%, p = .013, p(corr) = .039). The odds ratio was 2.48 (95% confidence interval: 1.14-5.58). There was no significant difference in the T-allele distribution in women. Including APOE4 status and age did not have an additional effect on the morbidity risk. Thus, our results support the idea that rs17571 confers an increased risk for AD in men but not in women. Further investigation should substantiate the role of gender for AD risk of rs17571.

Cathepsin D gene and the risk of Alzheimer's disease: a population-based study and meta-analysis

Cathepsin D (CTSD) is a gene involved in amyloid precursor protein processing and is considered a candidate for Alzheimer's disease (AD). The aim of the current study was to examine if variation in CTSD increases the risk of AD. We performed a candidate-gene analysis in a population-based cohort study (N=7983), and estimated the effect of CTSD on the risk of AD. Additionally, a large meta-analysis was performed incorporating our data and previously published data. The T-allele of CTSD rs17571 was associated with an increased risk of AD (p-value 0.007) in the Rotterdam Study. This association was predominantly found in APOE ε4 noncarriers. A meta-analysis of previously published data showed a significantly increased risk of AD in carriers of the T-allele of rs17571 (OR 1.22, 95% CI 1.03-1.44), irrespective of APOE ε4 carrier status. This study adds to the evidence that CTSD increases the risk of AD, although the effect size is moderate.

Effects of enriched environment on gene expression and signal pathways in cortex of hippocampal CA1 specific NMDAR1 knockout mice

N-methyl-D-aspartate glutamate receptor 1 (NMDAR1) plays a pivotal role in different forms of memory. Indeed, hippocampal CA1 region specific knockout (KO) of NMDAR1 in mice showed memory impairment. Recently, it has been reported that environmental enrichment enhanced memory and rescued the memory deficits of the NMDAR1-KO mice. It is well known that cortex has synaptic connections with hippocampus and is the storage region of the brain for long-term memory. To understand the molecular mechanisms of the memory impairments in the NMDAR1-KO mice, we have examined gene expression profiles in cortex from the receptor KO mice compared to wild type mice. Furthermore, since memory deficits were rescued after exposure of the NMDAR1-KO mice to enriched environment, we also analyzed the gene expression in the cortex of the KO mice after 3 hours, 2 days and 2 weeks enrichment. We found that the expression levels of 104 genes were altered in the cortex of NMDAR1-KO mice. Environmental enrichment for 3 hours, 2 days and 2 weeks affected the expression of 45, 34 and 56 genes, respectively. Genes involved in multiple signal pathways were regulated in the NMDAR1-KO mice, such as neurotransmission, structure, transcription, protein synthesis and protein processing. It is not surprising that since enriched environment rescued the memory decline in the NMDAR1-KO mice, the expression changes of a number of genes involved in these signal pathways were recovered or even reversed after enrichment. Our results further demonstrated that reelin and Notch signal pathways could be involved in the enrichment effects on memory improvement in the KO mice.

The cathepsin D rs17571 polymorphism: effects on CSF tau concentrations in Alzheimer disease

The lysosomal protease cathepsin D (CtsD, EC 3.4.23.5; gene, CTSD) has been associated with Alzheimer disease (AD) due to its cerebral expression being increased early in the course of AD; additionally, a CTSD exon 2 polymorphism (rs17571; NT_009237.17:g.569834T>C) may confer risk to AD. Functionally, it may be implicated in amyloid precursor protein (APP) processing and tau protein degradation. The objective of this study was to determine whether the CTSD exon 2 polymorphism affects cerebrospinal fluid (CSF), concentrations of beta-amyloid (Abeta42) and tau in two independent samples from Germany (n=73) and Sweden (n=66). Patients carrying the CTSD rs17571-T allele had significantly decreased CSF levels of tau (Munich, p=0.003; Swedish, p=0.029; combined sample, p<0.001), whereas no significant effect was observed on Abeta42 concentrations. Likewise, no significant impact was observed on Mini Mental State Examination (MMSE) scores. The data of both independent samples suggest that the CTSD rs17571 polymorphism does not affect APP processing but shows significant effects on tau processing. The result may corroborate the implication of the lysosomal system in the pathogenesis of AD and is of particular importance if CSF tau is used as a diagnostic biomarker.

Removal of the glycosylphosphatidylinositol anchor from PrP(Sc) by cathepsin D does not reduce prion infectivity

According to the protein-only hypothesis of prion propagation, prions are composed principally of PrP(Sc), an abnormal conformational isoform of the prion protein, which, like its normal cellular precursor (PrP(C)), has a GPI (glycosylphosphatidylinositol) anchor at the C-terminus. To date, elucidating the role of this anchor on the infectivity of prion preparations has not been possible because of the resistance of PrP(Sc) to the activity of PI-PLC (phosphoinositide-specific phospholipase C), an enzyme which removes the GPI moiety from PrP(C). Removal of the GPI anchor from PrP(Sc) requires denaturation before treatment with PI-PLC, a process that also abolishes infectivity. To circumvent this problem, we have removed the GPI anchor from PrP(Sc) in RML (Rocky Mountain Laboratory)-prion-infected murine brain homogenate using the aspartic endoprotease cathepsin D. This enzyme eliminates a short sequence at the C-terminal end of PrP to which the GPI anchor is attached. We found that this modification has no effect (i) on an in vitro amplification model of PrP(Sc), (ii) on the prion titre as determined by a highly sensitive N2a-cell based bioassay, or (iii) in a mouse bioassay. These results show that the GPI anchor has little or no role in either the propagation of PrP(Sc) or on prion infectivity.

Genetic associations between cathepsin D exon 2 C-->T polymorphism and Alzheimer's disease, and pathological correlations with genotype

Genetic variations represent major risk factors for Alzheimer's disease (AD). While familial early onset AD is associated with mutations in the amyloid precursor protein and presenilin genes, only the e4 allele of the apolipoprotein E (APOE) gene has so far been established as a genetic risk factor for late onset familial and sporadic AD. It has been suggested that the C-->T (224Ala-->Val) transition within exon 2 of the cathepsin D gene (CTSD) might represent a risk factor for late onset AD. The objective of this study was to investigate whether possession of the CTSD exon 2 T allele increases the risk of developing AD, and to determine whether this modulates the amyloid pathology of the disease in conjunction with, or independent of, the APOE e4 allele. Blood samples were obtained from 412 patients with possible or probable AD and brain tissues from a further 148 patients with AD confirmed by postmortem examination. CTSD and APOE genotyping were performed by PCR on DNA extracted from blood, or from frontal cortex or cerebellum in the postmortem cases. Pathological measures of amyloid beta protein (Abeta), as plaque Abeta40 and Abeta42(3) load and degree of cerebral amyloid angiopathy were made by image analysis or semiquantitative rating, respectively. CTSD genotype frequencies in AD were not significantly different from those in control subjects, nor did these differ between cases of early or late onset AD or between younger and older controls. There was no gene interaction between the CTSD T and APOE e4 alleles. The amount of plaque Abeta40 was greater in patients carrying the CTSD T allele than in non-carriers, and in patients bearing APOE e4 allele compared with non-carriers. Possession of both these alleles acted synergistically to increase levels of plaque Abeta40, especially in those individuals who were homozygous for the APOE e4 allele. Possession of the CTSD T allele had no effect on plaque Abeta42(3) load or degree of CAA. Possession of the CTSD T allele does not increase the risk of developing AD per se, but has a modulating effect on the pathogenesis of the disorder by increasing, in concert with the APOE e4 allele, the amount of Abeta deposited as senile plaques in the brain in the form of Abeta40.

The cathepsin D gene exon 2 (C224T) polymorphism and sporadic Alzheimer's disease in European populations

The cathepsin D gene (CTSD) exon 2 (C224T) polymorphism has been associated with an increased risk for sporadic Alzheimer's disease (AD), but with controversial findings. We studied CTSD exon 2 (C224T) and apolipoprotein E (APOE) genotype frequencies in 168 AD patients and 218 age-matched healthy controls from Southern Italy. No statistically significant differences were found in CTSD allele or genotype frequencies between AD patients and controls, and there were no interactions with sex or APOE genotype. Furthermore, comparing our results with the findings from other European populations, the CTSD*T allele frequency showed a statistically significant increasing trend from Northern to Southern regions of Europe in AD patients and controls (z=2.51, p<.01; z=4.02, p<.001, respectively), with a concomitant inverse trend for CTSD*C allele frequency. The regional differences in CTSD allele frequencies could be related to the different patterns of association between this polymorphism and AD in various European studies.

Proteolytic mechanisms in necrotic cell death and neurodegeneration

Programmed neuronal cell death is required during development to achieve the accurate wiring of the nervous system. However, genetic or accidental factors can lead to the premature, non-programmed death of neurons during adult life. Inappropriate death of cells in the nervous system is the cause of multiple neurodegenerative disorders. Pathological neuronal death can occur by apoptosis, by necrosis or by a combination of both. Necrotic cell death underlies the pathology of devastating neurological diseases such as neurodegenerative disorders, stroke or trauma. However, little is known about the molecular mechanisms that bring about necrotic cell death. Proteases play crucial roles in neuron degeneration by exerting both regulatory and catabolic functions. Elevated intracellular calcium is the most ubiquitous feature of neuronal death with the concomitant activation of cysteine calcium-dependent proteases, calpains. Calpains and lysosomal, catabolic aspartyl proteases, play key roles in the necrotic death of neurons. In this review, we survey the recent literature on the role of cysteine and aspartyl proteases in necrosis and neurodegeneration, aiming to delineate common proteolytic mechanisms mediating cellular destruction.

Lack of association of cathepsin D genetic polymorphism with Alzheimer's disease in Koreans

Cathepsin D (CatD) is a good candidate susceptibility marker for Alzheimer's disease (AD), since it was found to be involved in the processing of the amyloid precursor protein and the formation of the hyperphosphorylated tau. And recently, a CatD genetic polymorphism was found to be associated with the risk of Alzheimer's disease (AD) in a German population. However, the CatD T-AD association has not been replicated in a series of the successive independent studies in other races. Therefore, we determined CatD genotypes to examine the possible association of the CatD polymorphism with AD in Koreans. We failed to find significant association between the CatD T allele and AD. In addition, the CatD T--AD association was not significant regardless of the age at onset or the occurrence of the apolipoprotein epsilon4 allele. However, we cannot exclude the possible contribution of the CatD in the development of AD, since the power of the present study was not high enough because of low allelic frequency of the CatD T in Koreans and small sample size. In conclusion, the association between the CatD genetic polymorphism and AD was not found in Koreans, although it waits for further replication in an extended sample.

Contribution of apolipoprotein E and cathepsin D genotypes to the familial aggregation of Alzheimer's disease

OBJECTIVE

The familial aggregation of late-onset Alzheimer's disease (AD) might be caused by the clustering of genetic risk factors in families. This study investigates the influence of variants of candidate genes on the familial aggregation of AD.

METHODS

The occurrence of AD was examined in 1,420 first-degree relatives of 70 AD patients and 144 nondemented controls classified by the presence of AD and relevant candidate genes in index subjects.

RESULTS

Relatives of nondemented controls with an apolipoprotein E4 or a cathepsin D T allele had a higher cumulative lifetime incidence of AD than relatives of subjects without the respective alleles. This effect was not detected in relatives of AD patients. Variants of the interleukin-6, bleomycin hydrolase and alpha(2)-macroglobulin genes did not significantly influence the (age-adjusted) risk of AD in relatives.

CONCLUSIONS

Familial aggregation of late-onset AD is likely to be caused by several genetic risk factors. Variants of the apolipoprotein E and cathepsin D genes influenced the risk of AD in relatives of nondemented control subjects. The lack of an influence of these genotypes on the risk of AD in relatives of AD subjects may be the consequence of complementary reductions of other genetic risk factors such as various, yet unknown susceptibility genes in patients and, consequently, in their first-degree relatives.

Association between cathepsin D polymorphism and Alzheimer's disease in a Chinese Han population

Cathepsin D (CTSD) is an intracellular aspartyl protease, which is active in the endosomal/lysosomal system. CTSD may play a role in Alzheimer's disease (AD) through cleaving the amyloid precursor protein into beta-amyloid peptide and degrading tau protein into fragments. A functional polymorphism in exon 2 of the cathepsin D gene (C-->T, Ala224Val) has recently been reported to increase the risk for AD in some of the Caucasian populations, with a significant overrepresentation of the T allele, but these reports have not been universally duplicated. We performed an association study between CTSD polymorphism and AD in 156 sporadic AD patients and 183 controls of Chinese Han ethnicity. Our data revealed that the distribution of CTSD genotypes and alleles was similar in patients and controls. No direct association was found between CTSD polymorphism and AD risk. There might be a weak synergistic interaction between CTSD T and APOEepsilon4 allele in increasing the risk for developing AD.

Calcium-dependent and aspartyl proteases in neurodegeneration and ageing in C. elegans

Proteolytic mechanisms have been implicated in the process of ageing, and in many neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's diseases, which are most prevalent in old age. Simple model organisms such as the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster, which offer the prowess of sophisticated genetic approaches, have contributed to our understanding of ageing and neurodegeneration. Intensive research in these systems has resulted in detailed models of the ageing process, and also of several neurodegenerative diseases, which recapitulate same aspects of the human pathologies. Inappropriate cell death is a major component of these and other devastating conditions such as stroke. The dissection of the molecular mechanisms underlying the process of cell degeneration in ageing is of utmost importance. Evidence from investigations in C. elegans implicates deregulated proteolysis as one major determinant of cellular destruction in neurodegeneration and ageing, and suggests that the process depends critically on the activation of calcium-dependent, calpain proteases and lysosomal aspartyl proteases. Apart from shedding light on important but inadequately understood facets of such phenomena, these discoveries hold promise for developing novel, effective intervention strategies aiming to ameliorate or even counter inappropriate cell death.

Causative and susceptibility genes for Alzheimer's disease: a review

Alzheimer's disease (AD) is the most common type of dementia in the elderly population. Three genes have been identified as responsible for the rare early-onset familial form of the disease: the amyloid precursor protein (APP) gene, the presenilin 1 (PSEN1) gene and the presenilin 2 (PSEN2) gene. Mutations in these genes, however, account for less than 5% of the total number of AD cases. The remaining 95% of AD patients are mostly sporadic late-onset cases, with a complex aetiology due to interactions between environmental conditions and genetic features of the individual. In this paper, we review the most important genes supposed to be involved in the pathogenesis of AD, known as susceptibility genes, in an attempt to provide a comprehensive picture of what is known about the genetic mechanisms underlying the onset and progression of AD. Hypotheses about the role of each gene in the pathogenic pathway are discussed, taking into account the functions and molecular features, if known, of the coded protein. A major susceptibility gene, the apolipoprotein E (APOE) gene, found to be associated with sporadic late-onset AD cases and the only one, whose role in AD has been confirmed in numerous studies, will be included in a specific chapter. As the results reported by association studies are conflicting, we conclude that a better understanding of the complex aetiology that underlies AD may be achieved likely through a multidisciplinary approach that combines clinical and neurophysiological characterization of AD subtypes and in vivo functional brain imaging studies with molecular investigations of genetic components.

Simultaneous analysis of five genetic risk factors in Polish patients with Alzheimer's disease

As Alzheimer's disease (AD) is a complex disease, we decided to estimate how previously reported genetic polymorphisms interact to increase the risk for the disease. Five candidate genes were chosen: apolipoprotein E (APOE), alpha 2-macroglobulin, cathepsin D, myeloperoxidase and nitric oxide synthase. Genotyping was performed in 100 cases of late-onset AD and 100 healthy controls. We found a highly significant difference in APOE epsilon 4 distribution between groups (P<0.005). However, no evidence of association for other studied loci was found. Cumulative analysis of five genetic polymorphisms was performed, but it also failed to reveal any synergistic effect of candidate genes greater than that caused by APOE itself. Our results suggest that the APOE epsilon 4 allele is the only known genetic risk factor for late-onset, sporadic AD.

Cathepsin D exon 2 polymorphism associated with general intelligence in a healthy older population

General intelligence is a heritable trait that is a risk factor for both the onset of dementia and the rate of cognitive decline in community-dwelling older persons. Previous studies screening for quantitative trait loci (QTLs) that influence general intelligence in healthy individuals have identified four loci, two of which are located within the genes insulin-like growth factor 2 receptor (IGF2R) and the Msx1 homeobox. Here, we report the finding of another QTL associated with general intelligence that is located within exon 2 of the cathepsin D (CTSD) gene. A group of 767 healthy adults with a follow-up period of over 15 years have been analyzed for cross-sectional and longitudinal trends in cognitive change using the Heim intelligence test score (AH4-1). We observed a significant association (P = 0.01) between a functional C > T (Ala > Val) transition within exon 2 of the CTSD gene that increases the secretion of pro-CTSD from the cell, and the AH4-1 score at initial testing on entry to the longitudinal study. Interestingly, CTSD is transported by IGF2R from the trans Golgi network to the lysosome.

Cathepsin D polymorphism in Italian sporadic and familial Alzheimer's disease

A recent study has shown that a genetic variation in the Cathepsin D (catD) gene is a major risk factor for the development of Alzheimer's disease (AD). CatD is an intracellular aspartyl protease involved in neurodegeneration. A C-->T (Ala-->Val) transition at position 224 has been associated with altered intracellular maturation. Recently, a significant overrepresentation of the T allele of the catD gene in AD patients compared with controls was reported. However, this finding has not yet been confirmed. We analyzed the distribution of catD and apolipoprotein E polymorphisms in Italian patients with sporadic and familial AD (FAD). Our studies revealed that the distribution of catD polymorphism did not differ in AD and FAD patients and controls. Thus, our data do not support a role for the catD gene as a genetic risk factor in the development of AD.

Cerebrospinal fluid levels of beta-amyloid(42) in patients with Alzheimer's disease are related to the exon 2 polymorphism of the cathepsin D gene

The intracellular aspartyl protease cathepsin D (catD) is involved in such Alzheimer's disease (AD)-related processes as the activation of the endosomal/lysosomal system and the cleavage of the amyloid precursor protein into amyloidogenic components, which may initiate neurodegeneration. A non-synonymous polymorphism (exon 2, C to T exchange leading to ala-->val substitution) of the gene encoding catD (CTSD) was previously associated with AD, in that the T allele increased the risk for AD. To investigate whether the T allele is associated with disease-related traits, we measured the concentration of the amyloid beta-peptide 1-42 (Abeta(42)) and 1-40 (Abeta(40)) in patients and control subjects. The T allele of the CTSD genotype was associated with a 50% decrease in Abeta(42) levels in the cerebrospinal fluid. Thus, we demonstrate a significant impact of the CTSD genotype on Abeta(42) levels in the cerebrospinal fluid of AD patients and underpin the importance of the validation of susceptibility genes by examining their potential pathophysiological relevance.

Lack of association between cathepsin D genetic polymorphism and Alzheimer disease in a Spanish sample

Cathepsin D (catD) is an intracellular aspartyl protease that exhibits beta and gamma secretase-like activity to cleave amyloid precursor protein into beta amyloid peptide. The T-allele of a biallelic (alleles C and T) polymorphism in the exon 2 of the catD gene has been found to be associated with increased risk of Alzheimer disease (AD) in two independent German populations. Other groups have been unable to replicate this association in Caucasian American and Northern Ireland populations. Moreover, a small and no significant tendency for the T-allele to be protective for AD has been demonstrated in Caribbean Hispanics. A case control study utilizing a clinically well-defined group of 311 sporadic AD patients and 346 control subjects was performed to test this association in an ethnically homogeneous population from Spain. We did not observe any association between the T-allele of the catD gene and the disease. Furthermore, catD was not predictive of AD in an interactive fashion when considering apolipoprotein E, age, or gender.

Of replications and refutations: the status of Alzheimer's disease genetic research

Alzheimer's disease (AD) is a genetically complex and heterogeneous disorder. To date, mutations in three genes (APP, PSEN1, PSEN2) have been described to cause familial early-onset AD. In addition, a common polymorphism in the gene encoding apolipoprotein E (APOE) has been associated with the more common late-onset form of the disease. However, many studies have shown that genetic factors other than APOE play an important role in late-onset AD. Along these lines, a recent report predicted the existence of at least four additional late-onset AD genes, one of which was estimated to have a much greater contribution to age of onset variation than the APOE epsilon 4-allele. However, most of the nearly three dozen loci that have been proposed as putative AD genes to date have been followed by both replications and refutations, making consensus impossible. In this overview, we discuss the current status of genetic research in AD, including a brief summary of applicable analytic tools, and a summary of recent findings suggesting the existence of novel AD genes on chromosomes 10, 11, and 12.

Non-replication of association between cathepsin D genotype and late onset Alzheimer disease

In two recent studies from Germany, a strong association was found between the allelic variant T of the amino acid substitution encoding polymorphism 224 C/T (A38V) in exon 2 of the cathepsin D gene (CTSD) and late onset Alzheimer disease (AD). Other studies from Europe and the USA revealed ambiguous results. Therefore, we performed an independent association study on CTSD and AD in a sample of 324 Caucasian patients from Germany, Switzerland, and Italy with late onset AD, and 302 non-demented controls. We could not confirm an association between CTSD genotype and AD, although there was a slight but not significant increase in frequency of the T allele and T carrier status in AD. Post hoc data analyses suggested that there might be a stronger effect of CTSD genotype on AD risk in males, and an interaction between CTSD and APOE genotypes in males but not females.