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We analyzed the PRNP M129V polymorphism in a Dutch population-based early-onset Alzheimer's disease sample. We observed a significant association between early-onset Alzheimer's disease and homozygosity of M129V (odds ratio [OR], 1.9; 95% confidence interval [CI], 1.1-3.3; P = 0.02) with the highest risk for V homozygotes (OR, 3.2; 95% CI, 1.4-7.1; p < 0.01). In patients with a positive family history, these risks increased to 2.6 (95% CI, 1.3-5.3; p < 0.01) and 3.5 (95% CI, 1.3-9.3; p = 0.01), respectively.

We report the results of a genome-wide search in a four-generation pedigree with autosomal dominant early-onset dementia (mean onset age: 64.9 years, range 53-79 years). In this family we previously excluded the known Alzheimer's disease genes based on linkage analysis and mutation screening of the amyloid precursor protein gene (exons 16 and 17) and the presenilin 1 and 2 genes. In addition we excluded mutations in the prion protein gene and exons 9-13 of the microtubule associated protein tau (MAP7) gene. We obtained conclusive linkage with chromosome 17q21 markers with a maximum multi-point LOD score of 5.51 at D17S951 and identified a candidate region of 4.8 cM between D117S1787 and D17S958 containing MAPT. Recent clinical and neuropathological follow-up of the family showed that the phenotype most closely resembled frontotemporal dementia (FTD) characterized by dense ubiquitin-positive neuronal inclusions that were tau negative. Extensive mutation analysis of MAPT identified 38 sequence variations in exons, introns, untranslated regions and the 5' regulatory sequence, however none was comprised within the disease haplotype. Although our findings do not entirely exclude a mutation in a yet unanalyzed region of MAPT, the apparent absence of MAPT mutations combined with the lack of tau pathology is highly suggestive for another defective gene at 17q21 responsible for FTD in this family.

The apolipoprotein E (APOE) gene is involved in lipid transport. A common polymorphism in this gene with the APOE*2, APOE*3, and APOE*4 alleles influences plasma levels of apolipoprotein E and cholesterol. Besides its role in lipid transport, the APOE*4 allele is a genetic risk factor for Alzheimer disease (AD). Recently, a polymorphism in the APOE promoter region was found to be involved in plasma apolipoprotein E levels and was found associated with AD. We studied the effect of this -491A/T promoter polymorphism on plasma apolipoprotein E levels and risk for AD in a population-based case-control study. We found that there was a modest but statistically significant effect of the -491A/T polymorphism on plasma apolipoprotein E levels independent of the APOE genotype. The lowest plasma levels were measured for the AA genotype, highest levels for the TT genotype, and intermediate levels for the heterozygotes. There was a small effect of the -491 AA genotype on AD risk that disappeared after adjusting for APOE genotypes. Our data suggest that the -491A/T polymorphism has an APOE genotype-independent effect on plasma apolipoprotein E levels but no APOE-independent effect on AD risk.

The human TAR DNA binding protein 43 (TDP-43), encoded by the gene TARDBP, plays a central role in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. TDP-43 inclusions are also found in up to approximately 60% of Alzheimer's disease (AD) brains. Although ALS-causing TARDBP mutations cluster in the C-terminal glycine-rich region of the protein, the pathogenic nature of the atypical missense variants p.A90V (located between the bipartite nuclear localization signal) and p.D169G (located in the first RNA-binding domain) is unclear. In addition, whether causal ALS mutations represent gain or loss-of-function alleles remains unknown. We recently reported that loss-of-function of the highly conserved TARDBP ortholog in Drosophila (called TBPH) leads to death of bursicon neurons resulting in adult maturation and wing expansion defects. Here, we compared wild-type TARDBP, 2 typical ALS-causing mutations (p.G287S and p.A315T) and 2 atypical variants (p.A90V and p.D169G), for their ability to complement neuronal TBPH loss-of-function. Although p.D169G rescued organismal pupal lethality and neuronal loss to a similar extent as wild-type TARDBP, p.A90V, p.G287S, and p.A315T were less efficient. Accordingly, p.A90V, p.G287S, and p.A315T but not p.D169G or wild-type protein promoted a shift of TDP-43 from the nucleus to the cytoplasm in approximately 12%–14% of bursicon neurons. Finally, we found that the carrier frequency of rare variant p.A90V was higher in French-Belgian AD cases (5/1714, 0.29%) than in controls of European descent (5/9436, 0.05%) (odds ratio = 5.5; 95% confidence interval, 1.6–19.0; p = 0.009). We propose that pathogenic TARDBP mutations have partial loss-of-function properties and that TARDBP p.A90V may increase AD risk by the same mechanism.

Mutations in the gene coding for Sequestosome 1 (SQSTM1) have been genetically associated with amyotrophic lateral sclerosis (ALS) and Paget disease of bone. In the present study, we analyzed the SQSTM1 coding sequence for mutations in an extended cohort of 1,808 patients with frontotemporal lobar degeneration (FTLD), ascertained within the European Early-Onset Dementia consortium. As control dataset, we sequenced 1,625 European control individuals and analyzed whole-exome sequence data of 2,274 German individuals (total n = 3,899). Association of rare SQSTM1 mutations was calculated in a meta-analysis of 4,332 FTLD and 10,240 control alleles. We identified 25 coding variants in FTLD patients of which 10 have not been described. Fifteen mutations were absent in the control individuals (carrier frequency

We have previously reported a significant association between early-onset Alzheimer's disease (EOAD) and an allele in the promoter of presenilin 1 (PSEN1) significantly decreasing PSEN1 expression in vitro. For late-onset Alzheimer's disease (LOAD), numerous studies have reported inconsistent associations with a PSEN1 intronic polymorphism. We therefore hypothesized that linkage disequilibrium between the intronic PSEN1 polymorphism and the functional promoter polymorphism might explain the conflicting reports in LOAD. We analysed both variations in 356 LOAD patients and 230 controls in a population-based case-control study. In addition, we re-analysed all published literature on the PSEN1 intronic polymorphism in a metaanalysis. No significant association was found with the PSEN1 intronic or promoter polymorphism in our case-control sample. In the metaanalysis no major differences between patients and controls were found for the PSEN1 intronic variation. Together, our results do not support a major role for variable expression of PSEN1 in LOAD.

We describe a patient who was clinically diagnosed with familial early-onset Alzheimer disease (AD) carrying both the E318G substitution in presenilin 1 (PSEN1) and an insertion of 7 octapeptide coding repeats in the prion protein gene (PRNP). Neuropathological examination revealed elongated cerebellar prion protein deposits in the absence of AD pathology. Further analysis of other family members showed that the Creutzfeldt-Jakob disease phenotype in this family was caused solely by the PRNP insertion. This observation is consistent with our previous finding that PSEN1 E318G is not causally related to AD.

An intronic polymorphism affecting alternative splicing of exon 8 of ubiquilin 1 (UBQLN1), that is located at a well established Alzheimer's disease (AD) locus on chromosome 9q22, was recently associated with increased risk for late-onset AD. We analyzed this polymorphism in two independent AD samples consisting of patients with an onset age 70 years or less, but did not observe statistically significant association. Our study does not support a major role for this UBQLN1 polymorphism in AD patients with an earlier onset of disease.

Genome-wide association studies (GWAS) have identified a region upstream the BIN1 gene as the most important genetic susceptibility locus in Alzheimer's disease (AD) after APOE. We report that BIN1 transcript levels were increased in AD brains and identified a novel 3 bp insertion allele ∼28 kb upstream of BIN1, which increased (i) transcriptional activity in vitro, (ii) BIN1 expression levels in human brain and (iii) AD risk in three independent case-control cohorts (Meta-analysed Odds ratio of 1.20 (1.14-1.26) (P=3.8 × 10(-11))). Interestingly, decreased expression of the Drosophila BIN1 ortholog Amph suppressed Tau-mediated neurotoxicity in three different assays. Accordingly, Tau and BIN1 colocalized and interacted in human neuroblastoma cells and in mouse brain. Finally, the 3 bp insertion was associated with Tau but not Amyloid loads in AD brains. We propose that BIN1 mediates AD risk by modulating Tau pathology. ispartof: Molecular Psychiatry vol:18 issue:11 pages:1225-1234 ispartof: location:England status: published

TDP-43 proteinopathy is strongly implicated in the pathogenesis of amyotrophic lateral sclerosis and related neurodegenerative disorders. Whether TDP-43 neurotoxicity is caused by a novel toxic gain-of-function mechanism of the aggregates or by a loss of its normal function is unknown. We increased and decreased expression of TDP-43 (dTDP-43) in Drosophila. Although upregulation of dTDP-43 induced neuronal ubiquitin and dTDP-43-positive inclusions, both up- and downregulated dTDP-43 resulted in selective apoptosis of bursicon neurons and highly similar transcriptome alterations at the pupal-adult transition. Gene network analysis and genetic validation showed that both up- and downregulated dTDP-43 directly and dramatically increased the expression of the neuronal microtubule-associated protein Map205, resulting in cytoplasmic accumulations of the ecdysteroid receptor (EcR) and a failure to switch EcR-dependent gene programs from a pupal to adult pattern. We propose that dTDP-43 neurotoxicity is caused by a loss of its normal function. publisher: Elsevier articletitle: TDP-43 Loss-of-Function Causes Neuronal Loss Due to Defective Steroid Receptor-Mediated Gene Program Switching in Drosophila journaltitle: Cell Reports articlelink: http://dx.doi.org/10.1016/j.celrep.2012.12.014 content_type: article copyright: Copyright © 2013 The Authors. Published by Elsevier Inc. ispartof: Cell reports vol:3 issue:1 pages:160-172 ispartof: location:United States status: published

Autosomal recessive progressive external ophthalmoplegia (PEO) is one clinical disorder associated with multiple mitochondrial DNA deletions and can be caused by missense mutations in POLG, the gene encoding the mitochondrial DNA polymerase gamma. Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is another autosomal recessive disorder associated with PEO and multiple deletions of mitochondrial DNA in skeletal muscle. In several patients this disorder is caused by loss of function mutations in the gene encoding thymidine phosphorylase (TP). We report a recessive family with features of MNGIE but no leukoencephalopathy in which two patients carry three missense mutations in POLG, of which two are novel mutations (N846S and P587L). The third mutation was previously reported as a recessive POLG mutation (T251I). This finding indicates the need for POLG sequencing in patients with features of MNGIE without TP mutations.

Aggregates of the microtubule-associated protein Tau are neuropathological hallmark lesions in Alzheimer's disease (AD) and related primary tauopathies. In addition, Tau is genetically implicated in a number of human neurodegenerative disorders including frontotemporal dementia (FTD) and Parkinson's disease (PD). The exact mechanism by which Tau exerts its neurotoxicity is incompletely understood. Here, we give an overview of how studies using the genetic model organism Drosophila over the past decade have contributed to the molecular understanding of Tau neurotoxicity. We compare the different available readouts for Tau neurotoxicity in flies and review the molecular pathways in which Tau has been implicated. Finally, we emphasize that the integration of genome-wide approaches in human or mice with high-throughput genetic validation in Drosophila is a fruitful approach. ispartof: International Journal of Alzheimer's Disease vol:2012 pages:970980-970994 ispartof: location:United States status: published

The beta-site of beta-amyloid precursor protein cleaving enzyme (BACE) cleaves the beta-amyloid (Abeta) precursor protein at the N-terminal end of Abeta, allowing for the production of Abeta by C-terminal gamma-secretase cleavage. We hypothesized that over-activity of BACE might lead to the overproduction of Abeta, hence causing Alzheimer's disease (AD). Molecular genetic analyses of BACE in 9 autosomal dominant AD families and a population-based sample of 101 presenile AD cases did not identify genetic linkage, pathogenic mutations or genetic association with BACE, suggesting that BACE is not genetically involved in the etiology of AD.

BACKGROUND: m.14487T>C, a missense mutation (p.M63V) affecting the ND6 subunit of complex I of the mitochondrial respiratory chain, has been reported in isolated childhood cases with Leigh syndrome (LS) and progressive dystonia. Adult-onset phenotypes have not been reported. OBJECTIVES: To determine the clinical-neurological spectrum and associated mutation loads in an extended m.14487T>C family. METHODS: A genotype-phenotype correlation study of a Belgian five-generation family with 12 affected family members segregating m.14487T>C was carried out. Clinical and mutation load data were available for nine family members. Biochemical analysis of the respiratory chain was performed in three muscle biopsies. RESULTS: Heteroplasmic m.14487T>C levels (36-52% in leucocytes, 97-99% in muscle) were found in patients with progressive myoclonic epilepsy (PME) and dystonia or progressive hypokinetic-rigid syndrome. Patients with infantile LS were homoplasmic (99-100% in leucocytes, 100% in muscle). We found lower mutation loads (between 8 and 35% in blood) in adult patients with clinical features including migraine with aura, Leber hereditary optic neuropathy, sensorineural hearing loss and diabetes mellitus type 2. Despite homoplasmic mutation loads, complex I catalytic activity was only moderately decreased in muscle tissue. INTERPRETATION: m.14487T>C resulted in a broad spectrum of phenotypes in our family. Depending on the mutation load, it caused severe encephalopathies ranging from infantile LS to adult-onset PME with dystonia. This is the first report of PME as an important neurological manifestation of an isolated mitochondrial complex I defect.

Background: m.14487T>C, a missense mutation (p.M63V) affecting the ND6 subunit of complex I of the mitochondrial respiratory chain, has been reported in isolated childhood cases with Leigh syndrome (LS) and progressive dystonia. Adult-onset phenotypes have not been reported. Objectives: To determine the clinical–neurological spectrum and associated mutation loads in an extended m.14487T>C family. Methods: A genotype–phenotype correlation study of a Belgian five-generation family with 12 affected family members segregating m.14487T>C was carried out. Clinical and mutation load data were available for nine family members. Biochemical analysis of the respiratory chain was performed in three muscle biopsies. Results: Heteroplasmic m.14487T>C levels (36–52% in leucocytes, 97–99% in muscle) were found in patients with progressive myoclonic epilepsy (PME) and dystonia or progressive hypokinetic-rigid syndrome. Patients with infantile LS were homoplasmic (99–100% in leucocytes, 100% in muscle). We found lower mutation loads (between 8 and 35% in blood) in adult patients with clinical features including migraine with aura, Leber hereditary optic neuropathy, sensorineural hearing loss and diabetes mellitus type 2. Despite homoplasmic mutation loads, complex I catalytic activity was only moderately decreased in muscle tissue. Interpretation: m.14487T>C resulted in a broad spectrum of phenotypes in our family. Depending on the mutation load, it caused severe encephalopathies ranging from infantile LS to adult-onset PME with dystonia. This is the first report of PME as an important neurological manifestation of an isolated mitochondrial complex I defect.

Hyperphosphorylated microtubule associated protein tau, present in neurofibrillary tangles, is a prominent pathological feature of Alzheimer's disease (AD). The gene encoding tau (MAPT) was recently found mutated in frontotemporal dementia (FTD) and other tauopathies. We studied MAPT as a candidate gene in the etiology of AD. The study population consisted of 101 early-onset AD patients and 117 controls. Mutation analysis did not detect causal mutations in exons 9 to 13 encoding the microtubule-binding domains involved in FTD, however, two novel polymorphisms were detected in exon 9. Using the Ala169 polymorphism in exon 9 and a previously reported (CA)n-repeat polymorphism in intron 9, an association study was performed. No association with early-onset AD was detected. Together, our data indicate that MAPT does not play a role in early-onset AD.

Null mutations in the progranulin gene (GRN, PGRN) were recently identified as the causal mechanism underlying frontotemporal dementia (FTD) with ubiquitin-positive brain pathology linked to chromosome 17 (FTDU-17). In a Belgian and French FTD series comprising 332 patients, we reported 13 PGRN null mutations which were mainly nonsense and frameshift mutations resulting in premature stop codons. Here we report in the same patient series three missense mutations of which two (c.743C>T, p.Pro248Leu and c.1294C>T, p.Arg432Cys) were predicted in silico to severely affect protein folding and/or processing leading to PGRN protein haploinsufficiency. In addition, we observed three sequence variations in the 5' regulatory region that might potentially affect PGRN transcription activity. Our findings extend the mutation spectrum in PGRN leading to loss of functional PGRN as the basis for FTD. © 2007 Wiley-Liss, Inc.

The nuclear TAR DNA binding protein (TDP-43) is deposited in ubiquitin-positive inclusions in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS), two clinicopathologically overlapping neurodegenerative diseases. In this study we excluded mutations and copy number variations in the gene encoding TDP-43 (TARDBP) from an extended series of 173 FTD and 237 ALS patients. Further, we did not identify association of common genetic variants in these patients. Our data implicate that TDP-43 has no primary genetic role in the pathophysiological mechanisms underlying central nervous system neurodegeneration in these diseases.

To determine whether apolipoprotein alleles (APOE) influence behavioral and psychological signs and symptoms of dementia (BPSD), we initiated a prospective, longitudinal study. Patients with Alzheimer's disease (AD) (N = 186), frontotemporal dementia (FTD) (N=29), mixed dementia (MXD) (N= 28), dementia with Lewy bodies (DLB) (N= 11) and Parkinson's disease dementia (PDD) (N = 7) were included. Blood was collected for DNA extraction and APOE genotyping. Behavioral assessments were performed at baseline and semi-annually thereafter, using behavioral assessment scales (Middelheim frontality score, behavioral pathology in Alzheimer's disease rating scale (Behave-AD)). In FTD patients, we identified close dependent effects of APOE epsilon 4 on the Behave-AD total and cluster aggressiveness scores. APOE epsilon 2 was associated with a higher score on the Behave-AD cluster delusions in PDD/DLB patients. No APOE effects on frequency or severity of BPSD in AD and MXD Patients Were found. In Conclusion, APOE has disease-specific effects on BPSD in FTD and PDD/DLB patients, given the reported associations of APOE epsilon 4 with aggression (FTD) and of APOE epsilon 2 with delusions (PDD/DLB). (C) 2005 Elsevier Inc. All rights reserved.

The varied ways in which mutations in presenilins (PSEN1 and PSEN2) affect amyloid b precursor protein (APP) processing in causing early-onset familial Alzheimer disease (FAD) are complex and not yet properly understood. Nonetheless, one useful diagnostic marker is an increased ratio of Ab42 to Ab40 (Ab42/Ab40) in patients' brain and biological fluids as well as in transgenic mice and cells. We studied Ab and APP processing for a set of nine clinical PSEN mutations on a novel and highly reproducible enzyme-linked immunosorbent assay (ELISA)-based in vitro method and also sought correlation with brain Ab analyzed by image densitometry and mass spectrometry. All mutations significantly increased Ab42/Ab40 in vitro by significantly decreasing Ab40 with accumulation of APP C-terminal fragments, a sign of decreased PSEN activity. A significant increase in absolute levels of Ab42 was observed for only half of the mutations tested. We also showed that age-of-onset of PSEN1-linked FAD correlated inversely with Ab42/Ab40 (r=–0.89; P=0.001) and absolute levels of Ab42 (r=–0.83; P=0.006), but directly with Ab40 levels (r=0.69; P=0.035). These changes also partly correlated with brain Ab42 and Ab40 levels. Together, our data suggested that Ab40 might be protective by perhaps sequestering the more toxic Ab42 and facilitating its clearance. Also, the in vitro method we describe here is a valid tool for assaying the pathogenic potential of clinical PSEN mutations in a molecular diagnostic setting. Hum Mutat 27(7), 686–695, 2006. Published 2006 Wiley-Liss, Inc.

Frontotemporal dementia (FTD) with ubiquitin-immunoreactive neuronal inclusions ( both cytoplasmic and nuclear) of unknown nature has been linked to a chromosome 17q21 region (FTDU-17) containing MAPT (microtubule-associated protein tau)(1-3). FTDU-17 patients have consistently been shown to lack a tau-immunoreactive pathology(1-3), a feature characteristic of FTD with parkinsonism linked to mutations in MAPT (FTDP-17)(4). Furthermore, in FTDU-17 patients, mutations in MAPT and genomic rearrangements in the MAPT region have been excluded by both genomic sequencing(5) and fluorescence in situ hybridization on mechanically stretched chromosomes(6). Here we demonstrate that FTDU-17 is caused by mutations in the gene coding for progranulin (PGRN), a growth factor involved in multiple physiological and pathological processes including tumorigenesis(7). Besides the production of truncated PGRN proteins due to premature stop codons(8), we identified a mutation within the splice donor site of intron 0 (IVS0+5G> C), indicating loss of the mutant transcript by nuclear degradation. The finding was made within an extensively documented Belgian FTDU-17 founder family(3). Transcript and protein analyses confirmed the absence of the mutant allele and a reduction in the expression of PGRN. We also identified a mutation ( c. 3G>A) in the Met1 translation initiation codon, indicating loss of PGRN due to lack of translation of the mutant allele. Our data provide evidence that PGRN haploinsufficiency leads to neurodegeneration because of reduced PGRN-mediated neuronal survival. Furthermore, in a Belgian series of familial FTD patients, PGRN mutations were 3.5 times more frequent than mutations in MAPT, underscoring a principal involvement of PGRN in FTD pathogenesis.

We report the cytogenetic findings in a case of mixed germ cell-sex cord-stromal tumor of the ovary in a 5-month-old girl. Monosomy 22 was observed as the sole karyotypic abnormality. This result was confirmed by comparative genomic hybridization, which revealed no additional chromosomal imbalances. This is the first observation of a chromosomal aberration in a mixed germ cell-sex cord-stromal tumor of the ovary. Monosomy 22 has been previously observed in granulosa cell tumors of the ovary. This could suggest a common pathogenetic pathway for both types of tumors.

In contrast to the common and genetically complex senile form of Alzheimer's disease (AD), the molecular genetic dissection of inherited presenile dementias has given important mechanistic insights into the pathogenesis of degenerative brain disease. Here, we focus on recent genotype-phenotype correlative studies in presenile AD and the frontotemporal dementia (FTD) complex of disorders. Together, these studies suggest that AD and FTD are linked in a genetic spectrum of presenile degenerative brain disorders in which tau appears to be the central player.

We obtained conclusive linkage of Alzheimer disease (AD) with a candidate region of 19.7 cM at 7q36 in an extended multiplex family, family 1270, ascertained in a population-based study of early-onset AD in the northern Netherlands. Single-nucleotide polymorphism and haplotype association analyses of a Dutch patient-control sample further supported the linkage at 7q36. In addition, we identified a shared haplotype at 7q36 between family 1270 and three of six multiplex AD-affected families from the same geographical region, which is indicative of a founder effect and defines a priority region of 9.3 cM. Mutation analysis of coding exons of 29 candidate genes identified one linked synonymous mutation, g.3803OG -> C in exon 10, that affected codon 626 of the PAX transactivation domain interacting protein gene (PAXIP1). It remains to be determined whether PAXIP1 has a functional role in the expression of AD in family 1270 or whether another mutation at this locus explains the observed linkage and sharing. Together, our linkage data from the informative family 1270 and the association data in the population-based early-onset AD patient-control sample strongly support the identification of a novel AD locus at 7q36 and re-emphasize the genetic heterogeneity of AD.

Familial forms of frontotemporal dementia (FTD) are in 10–43% of patients, caused by mutations in the gene encoding the microtubule associated protein tau (MAPT) located at chromosome 17q21. Neuropathologically, these patients are characterized by tau-positive depositions in brain. However, autosomal dominant forms of FTD without MAPT mutations have been reported, suggesting other tauopathy-related genetic defects. One such form is FTD linked to 17q21, with tau-negative but ubiquitine-positive neuronal inclusions or FTD-U. We previously reduced the candidate chromosomal region to 4.8 cM in a Dutch FTD-U family, 1083. A mutation in MAPT was excluded by genomic sequencing. More recently, we identified three Belgian FTD families of which two, DR2 and DR8, showed linkage to the 17q21 region. Both families shared a common haplotype in an 8.04 cM region, indicating that they are genetically related to a common founder. In the third family, DR7, we obtained an autopsy confirmation of the characteristic ubiquitin-positive, tau-negative neuronal inclusions. Currently, there are 11 FTD families linked to 17q21 that do not segregate a MAPT mutation, of which five are conclusively linked (LOD score > 3). Together the data suggest that FTD-U could represent an important subtype of FTD, and that identification of the underlying gene defect might significantly contribute to our understanding of the pathomechanism leading to neurodegeneration in this dementia subtype.

Familial frontotemporal dementia (FTD), characterized by tau-negative, ubiquitin-positive inclusions at autopsy, is linked to a chromosomal region at 17q21 (FTDU-17), encompassing the gene encoding the microtubule associated protein tau, MAPT. Mutations in MAPT were previously identified in familial FTD with parkinsonism (FTDP-17); however, in FTDU-17 patients, no pathogenic mutations were found in exonic regions consistent with the lack of tauopathy in FTDU-17 brains. Here, we excluded mutations in MAPT by genomic sequencing of 138.5 kb in FTDU-17 patients. Next, to facilitate the identification of the actual underlying genetic defect, we assembled the 6.5 Mb FTDU-17 sequence. Annotation demonstrated that MAPT is surrounded by three highly homologous low-copy repeats (LCRs) in a region of 1.7 Mb. Using evolutionary studies, short tandem repeat-based linkage disequilibrium (LD) and macro-restriction mapping, we demonstrated that these LCRs are at the basis of a series of rearrangements in the MAPT genomic region. One is an inversion that occurred 3 million years ago and resulted in a common polymorphism in humans to date. This inversion plus flanking LCRs spanned similar to 1.3 Mb and was shown to underlie the extended LD and haplotypes H1 and H2 across MAPT. However, in the FTDU-17 families, we ascertained segregation analysis precluding a relationship between the FTDU-17 and the H1/H2 inversion. The presence of multiple homologous LCRs in the region predicts that other potentially more complex genomic rearrangements might be underlying FTDU-17.

The authors previously reported that genetic variation in the gene coding for nicastrin (NCSTN) modified risk for familial early-onset Alzheimer disease (AD) in a Dutch population-based sample. Risk was highest in patients without an APOE epsilon4 allele. Here, they evaluated if NCSTN polymorphisms increased risk of AD in the eastern Finnish population. A significant difference in one haplotype was observed in AD patients without the APOE epsilon4 allele.

The prion protein gene (PRNP) plays a central role in the origin of Creutzfeldt-Jakob disease (CJD), but there is growing interest in other polymorphisms that may be involved in CJD. Polymorphisms upstream of PRNP that may modulate the prion protein production as well as polymorphisms in the prion-like doppel gene (PRND) have been studied, with inconsistent findings. We investigated the role of a single-nucleotide polymorphism (SNP 1368) located upstream of PRNP and three polymorphisms in PRND (T26M, P56L and T174M) in CJD. The study included a population-based sample of 52 patients with sporadic CJD and 250 controls. We analysed our data as single markers and haplotypes. Further, we conducted a meta-analysis on PRND T174M comparing the data of the four studies conducted to date. For SNP 1368 and PRNP M129V, we found significant evidence for linkage disequilibrium. No evidence was found for a relation of SNP 1368 to CJD independent of PRNP M129V. We further found a significant increased prevalence of M homozygotes at PRND T174M among sporadic CJD patients, when adjusting the analyses for the other genotypes. In the haplotype analyses, the association was strongest for persons homozygous for PRNP 129M and PRND 174M (odds ratio 4.35, 95% confidence interval 1.05-8.09; P=0.04). The meta-analysis on the PRND T174M polymorphism did not show a consistent effect across studies, raising the question as to whether PRND 174M is causally related to CJD, or whether the PRND allele is in linkage disequilibrium with another polymorphism related to CJD.

The authors conducted a prospective study of neurodegenerative and vascular dementia in Belgium. Strict diagnostic inclusion criteria were used to include well defined patients and controls. The results of apolipoprotein E (APOE) genotype effect on risk and clinical characteristics are presented.APOE genotyping was performed in patients with probable Alzheimer's disease (AD) (n=504), frontotemporal dementia (FTD) (n=47), vascular dementia (VaD) (n=152), mixed dementia (n=132), mild cognitive impairment (MCI) (n=44), Parkinson's disease (PD) (n=30), dementia with Lewy bodies (DLB) (n=17), and multisystem atrophy (MSA)/progressive supranuclear palsy (PSP) (n=12).The APOE allele frequencies of this Belgian control population (epsilon 2: 6.9%; epsilon 3: 76.2%; epsilon 4: 16.9%) did not differ from those reported for other white populations. AD, MCI, and mixed dementia patients had higher APOE epsilon 4 (32.9%, 38.6%, and 28.4% respectively) and lower APOE epsilon 3 (62.2%, 53.4%, and 66.3%) frequencies compared with controls, whereas only AD and mixed dementia patients had lower APOE epsilon 2 frequencies (4.9% and 5.3%). Apart from a borderline significant different distribution of APOE allele frequencies in VaD patients compared with controls, no other differences were detected. The influence of APOE epsilon 4 on clinical features of dementia was limited to lower age at onset in AD patients and a less pronounced negative correlation between age at onset and number of epsilon 4 alleles in MCI and mixed dementia patients.This study confirmed the risk association between APOE epsilon 4 and AD. The observation that APOE epsilon 4 is associated with mixed dementia reflected the role of AD in the aetiopathogenesis of this condition. Although MCI is an aetiologically heterogeneous syndrome, the increased APOE epsilon 4 frequencies indicated that a large proportion of the MCI patients included in the study might be predisposed to develop AD.

Autosomal recessive progressive external ophthalmoplegia is a mitochondrial disease characterized by accumulation of multiple large-scale deletions of mitochondrial DNA. We previously reported missense mutations in POLG, the gene encoding the mitochondrial DNA polymerase gamma in two nuclear families compatible with autosomal recessive progressive external ophthalmoplegia. Here, we report a novel POLG missense mutation (R627W) in a sporadic patient and we provide genetic support that all these POLG mutations are actually causal and recessive. The novel patient presented with sensory ataxic neuropathy and has the clinical triad of sensory ataxic neuropathy, dysarthria and ophthalmoparesis (SANDO). This is the first finding of a genetic cause of Sensory Ataxic Neuropathy, Dysarthria and Ophthalmoparesis and it implies that this disorder may actually be a variant of autosomal recessive progressive external ophthalmoplegia. Sensory neuropathy is the initial feature in Belgian compound heterozygote autosomal recessive progressive external ophthalmoplegia patients, all carrying the POLG A467T mutation, which occurs at a frequency of 0.6% in the Belgian population.

Nicastrin regulates gamma-secretase cleavage of the amyloid precursor protein by forming complexes with presenilins, in which most mutations causing familial early-onset Alzheimer disease (EOAD) have been found. The gene encoding nicastrin (NCSTN) maps to 1q23, a region that has been linked and associated with late-onset Alzheimer disease (LOAD) in various genome screens. In 78 familial EOAD cases, we found 14 NCSTN single-nucleotide polymorphisms (SNPs): 10 intronic SNPs, 3 silent mutations, and 1 missense mutation (N417Y). N417Y is unlikely to be pathogenic, since it did not alter amyloid beta secretion in an in vitro assay and its frequency was similar in case and control subjects. However, SNP haplotype estimation in two population-based series of Dutch patients with EOAD (n=116) and LOAD (n=240) indicated that the frequency of one SNP haplotype (HapB) was higher in the group with familial EOAD (7%), compared with the LOAD group (3%) and control group (3%). In patients with familial EOAD without the APOE epsilon4 allele, the HapB frequency further increased, to 14%, resulting in a fourfold increased risk (odds ratio = 4.1; 95% confidence interval 1.2-13.3; P=.01). These results are compatible with an important role of gamma-secretase dysfunction in the etiology of familial EOAD.

At least 13 loci responsible for autosomal dominant cerebellar ataxia (ADCA) have been identified. Spinocerebellar ataxia 1, 2, 3, 6 and 7 are caused by translated CAG repeat expansions. However, in France, >30% of ADCAs are not explained by the known genes. Recently, analysis of the TATA box-binding protein (TBP) gene, one of the transcription factors known to contain a CAG/CAA repeat, in patients with progressive cerebellar ataxia revealed one sporadic case with 63 repeats. We examined this gene in 162 index cases with ADCA. An expanded repeat with 46 repeat units was detected in a single index case from Belgium. In this family, two affected members and six unaffected, but at-risk, individuals carried expanded alleles. Interestingly, the expanded repeat was stable during transmission. The main clinical features in six patients were cerebellar ataxia, dementia and behavioural disturbances with onset in their fourth to sixth decade. The main neuropathological finding was severe neuronal loss and gliosis in the Purkinje cell layer. Immunohistochemical analysis showed neuronal intranuclear inclusions containing expanded polyglutamine, indicating that this disease shares several features with other polyglutamine diseases. This study demonstrates that CAG/CAA repeat expansion in the TBP gene causes ADCA with dementia and/or psychiatric manifestations.

There is growing evidence that vascular factors are involved in AD.1 In light of these findings, a polymorphism in the cystatin C gene ( CST3 ) that was recently found to be associated with late onset AD is a promising candidate gene.2 Cystatin C is an amyloidogenic protein found together with β-amyloid in the arteriolar walls of patients with AD and patients with congophilic amyloid angiopathy (CAA).3 As CAA is also a prominent feature in early onset AD and Down syndrome4 and a mutation in cystatin C leads to CAA at very early age5 we investigated the role of the CST3 polymorphism in early onset AD. Patients were derived from a population-based study of early onset AD in the Netherlands, as described in detail before.6 AD was diagnosed using a protocol in accordance with the National Institute of Neurological and Communicative Disorders and Stroke–Alzheimer’s …

We investigated the risk associated with the codon 129 polymorphism in the prion protein gene (PRNP) and apolipoprotein E gene (APOE) isoforms for development of Creutzfeldt-Jakob disease (CJD) (n=126) and the possible influences on the disease pathology and its most important clinical characteristics. The PRNP M129V (PRNP129) polymorphism was determined using both DNA extracted from formalin fixed and paraffin embedded brain tissue (n=59) and leukocyte extracted DNA (n=67). In the latter group also the PRNP open reading frame and the APOE genotype were analysed and compared to a neurologically unaffected, age and sex matched control group (n=79). We found that methionine homozygosity of the PRNP129 increases the risk for developing CJD. PRNP129 also influenced the prion accumulation patterns in brain. The APOE 4 allele was an independent risk factor for developing CJD. We further observed a significant dose dependent APOE 4 effect on the number and type of amyloid-beta plaques in the brain of CJD patients.

Progressive external ophthalmoplegias (PEO) characterized by accumulation of large-scale mitochondrial DNA (mtDNA) deletions are rare human diseases. We mapped a new locus for dominant PEO at 15q22-q26 in a Belgian pedigree and identified a heterozygous mutation (Y955C) in the polymerase motif B of the mtDNA polymerase gamma (POLG). We identified three additional POLG missense mutations compatible with recessive PEO In two nuclear families. POLG is the only DNA polymerase responsible for mtDNA replication.

The dense-cored plaques are considered the pathogenic type of amyloid deposition in Alzheimer's disease brains because of their predominant association with dystrophic neurites. Nevertheless, in >90% of cases of Alzheimer's disease amyloid is also deposited in cerebral blood vessel walls (congophilic amyloid angiopathy; CAA) but its role in Alzheimer's disease pathogenesis remains enigmatic. Here, we report a family (family GB) in which early-onset Alzheimer's disease was caused by a novel presenilin 1 mutation (L282V). This was unusually severe CAA reminiscent of the Flemish amyloid precursor protein (A692G) mutation we reported previously, which causes Alzheimer's disease and/or cerebral haemorrhages. In family GB, however, the disease presented as typical progressive Alzheimer's disease in the absence of strokes or stroke-like episodes. Similarly, neuroimaging studies and neuropathological examination favoured a degenerative over a vascular dementia. Interestingly, an immunohistochemical study revealed that, similar to causing dense-cored amyloid plaques, CAA also appeared capable of instigating a strong local dystrophic and inflammatory reaction. This was suggested by the observed neuronal loss, the presence of tau- and ubiquitin-positive neurites, micro- and astrogliosis, and complement activation. Together, these data suggest that, like the dense-cored neuritic plaques, CAA might represent a pathogenic lesion that contributes significantly to the progressive neurodegeneration that occurs in Alzheimer's disease.

Mutations in the presenilin 1 ( PSEN1 ) gene have been implicated in 18-50% of autosomal dominant cases with early-onset Alzheimer's disease (EOAD). Also, PSEN1 has been suggested as a potential risk gene in late-onset AD cases. We recently showed genetic association in a population-based study of EOAD, pointing to the 5' regulatory region of PSEN1. In this study we systematically screened 3.5 kb of the PSEN1 upstream region and found four novel polymorphisms. Genetic analysis confirmed association of two polymorphisms with increased risk for EOAD. In addition, we detected two different mutations in EOAD cases at-280 and-2818 relative to the transcription initiation site in exon 1A of PSEN1. Analysis of the mutant and wild-type-280 variants using luciferase reporter gene expression in transiently transfected neuroblastoma cells showed a 30% decrease in transcriptional activity for the mutant-280G PSEN1 promoter variant compared with the wild-type variant-280C. Our data suggest that the increased risk for EOAD associated with PSEN1 may result from genetic variations in the regulatory region leading to altered expression levels of the PSEN1 protein.

Background: Whereas several authors recently reported a positive association between the α2-macroglobulin gene ( A2M ) and late-onset AD (LOAD), others were unable to replicate these findings. Early-onset AD (EOAD) is defined as onset age 65 years of age. Objective: To evaluate the role of A2M in AD, the authors conducted a population-based study of EOAD and LOAD as well as a meta-analysis of all studies conducted to date. Methods: Patients with EOAD (n = 100) were derived from a population-based study in four northern provinces of the Netherlands and the area of metropolitan Rotterdam. Patients with LOAD (n = 344) were drawn from the Rotterdam Study, a population-based prospective study on residents aged 55 years and over of a Rotterdam suburb in the Netherlands. Two polymorphisms were studied, A2M- I/D and A2M- Ile1000Val, in relation to the APOE e4 allele ( APOE *4). Results: No genotypic or allelic association was found for either polymorphism in the population-based series of patients with LOAD. In patients with EOAD without APOE *4, a significant increase of carriers of A2M -1000Val was found. The meta-analysis of available published case–control data on these polymorphisms in white and mixed ethnic populations yielded no significant differences between cases and controls. Pooling the Asian studies conducted to date showed a significant decrease in the frequency of A2M -D among patients. Conclusions: These results suggest that A2M is not genetically associated with LOAD in white patients or mixed populations as found in the United States. In these populations A2M does not have clinical relevance. From a scientific perspective, the findings on EOAD and Asian patients require replication and further research in the A2M region.