John C. van Swieten

A hexanucleotide repeat expansion in C9ORF72 is the cause of chromosome 9p21-linked ALS-FTD

The chromosome 9p21 amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD) locus contains one of the last major unidentified autosomal-dominant genes underlying these common neurodegenerative diseases. We have previously shown that a founder haplotype, covering the MOBKL2b, IFNK, and C9ORF72 genes, is present in the majority of cases linked to this region. Here we show that there is a large hexanucleotide (GGGGCC) repeat expansion in the first intron of C9ORF72 on the affected haplotype. This repeat expansion segregates perfectly with disease in the Finnish population, underlying 46.0% of familial ALS and 21.1% of sporadic ALS in that population. Taken together with the D90A SOD1 mutation, 87% of familial ALS in Finland is now explained by a simple monogenic cause. The repeat expansion is also present in one-third of familial ALS cases of outbred European descent, making it the most common genetic cause of these fatal neurodegenerative diseases identified to date.

Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: A cross-sectional study

Summary Background We aimed to accurately estimate the frequency of a hexanucleotide repeat expansion in C9orf72 that has been associated with a large proportion of cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Methods We screened 4448 patients diagnosed with ALS (El Escorial criteria) and 1425 patients with FTD (Lund-Manchester criteria) from 17 regions worldwide for the GGGGCC hexanucleotide expansion using a repeat-primed PCR assay. We assessed familial disease status on the basis of self-reported family history of similar neurodegenerative diseases at the time of sample collection. We compared haplotype data for 262 patients carrying the expansion with the known Finnish founder risk haplotype across the chromosomal locus. We calculated age-related penetrance using the Kaplan-Meier method with data for 603 individuals with the expansion. Findings In patients with sporadic ALS, we identified the repeat expansion in 236 (7·0%) of 3377 white individuals from the USA, Europe, and Australia, two (4·1%) of 49 black individuals from the USA, and six (8·3%) of 72 Hispanic individuals from the USA. The mutation was present in 217 (39·3%) of 552 white individuals with familial ALS from Europe and the USA. 59 (6·0%) of 981 white Europeans with sporadic FTD had the mutation, as did 99 (24·8%) of 400 white Europeans with familial FTD. Data for other ethnic groups were sparse, but we identified one Asian patient with familial ALS (from 20 assessed) and two with familial FTD (from three assessed) who carried the mutation. The mutation was not carried by the three Native Americans or 360 patients from Asia or the Pacific Islands with sporadic ALS who were tested, or by 41 Asian patients with sporadic FTD. All patients with the repeat expansion had (partly or fully) the founder haplotype, suggesting a one-off expansion occurring about 1500 years ago. The pathogenic expansion was non-penetrant in individuals younger than 35 years, 50% penetrant by 58 years, and almost fully penetrant by 80 years. Interpretation A common Mendelian genetic lesion in C9orf72 is implicated in many cases of sporadic and familial ALS and FTD. Testing for this pathogenic expansion should be considered in the management and genetic counselling of patients with these fatal neurodegenerative diseases. Funding Full funding sources listed at end of paper (see Acknowledgments).

Cerebral hypoperfusion and clinical onset of dementia: The Rotterdam study

Cerebral blood flow (CBF) velocity is decreased in patients with Alzheimers disease. It is being debated whether this reflects diminished demand because of advanced neurodegeneration or that cerebral hypoperfusion contributes to dementia. We examined the relation of CBF velocity as measured with transcranial Doppler with dementia and markers of incipient dementia (ie, cognitive decline and hippocampal and amygdalar atrophy on magnetic resonance imaging) in 1,730 participants of the Rotterdam Study aged 55 years and older. Cognitive decline in the 6.5 years preceding CBF velocity measurement was assessed with repeated Mini‐Mental State Examinations in nondemented subjects (n = 1,716). Hippocampal and amygdalar volumes were assessed in a subset of 170 nondemented subjects. Subjects with greater CBF velocity were less likely to have dementia. Furthermore, in nondemented subjects, greater CBF velocity was related to significantly less cognitive decline over the preceding period (odds ratio per standard deviation increase in mean CBF 0.74 [95% confidence interval, 0.58–0.98]) and larger hippocampal and amygdalar volumes. A low CBF is associated with dementia, but also with markers of incipient dementia. Although we cannot exclude that this is caused by preclinical neurodegeneration leading to hypoperfusion, it does suggest that cerebral hypoperfusion precedes and possibly contributes to onset of clinical dementia. Ann Neurol 2005;57:789–794

Alcohol consumption and risk of dementia: the Rotterdam Study

BACKGROUND Light-to-moderate alcohol consumption reduces the risk of coronary heart disease and stroke. Because vascular disease is associated with cognitive impairment and dementia, we hypothesised that alcohol consumption might also affect the risk of dementia. METHODS We examined the relation between alcohol consumption and risk of dementia in individuals taking part in the Rotterdam Study--a prospective population-based study of 7983 individuals aged 55 years and older. We studied all participants who did not have dementia at baseline (1990-93) and who had complete data on alcohol consumption (n=5395). Through follow-up examinations in 1993-94 and 1997-99 and an extensive monitoring system, we obtained nearly complete follow-up (99.7%) until the end of 1999. We used proportional hazards regression analysis, adjusted for age, sex, systolic blood pressure, education, smoking, and body-mass index, to compare the risk of developing dementia between individuals who regularly consumed alcohol and individuals who did not consume alcohol. FINDINGS The average follow-up was 6.0 years. During this period, 197 individuals developed dementia (146 Alzheimers disease, 29 vascular dementia, 22 other dementia). The median alcohol consumption was 0.29 drinks per day. Light-to-moderate drinking (one to three drinks per day) was significantly associated with a lower risk of any dementia (hazard ratio 0.58 [95% CI 0.38-0.90]) and vascular dementia (hazard ratio 0.29 [0.09-0.93]). We found no evidence that the relation between alcohol and dementia varied by type of alcoholic beverage. INTERPRETATION These findings suggest that light-to-moderate alcohol consumption is associated with a reduced risk of dementia in individuals aged 55 years or older. The effect seems to be unchanged by the source of alcohol.

High prevalence of mutations in the microtubule-associated protein tau in a population study of frontotemporal dementia in the Netherlands

Mutations in microtubule-associated protein tau recently have been identified in familial cases of frontotemporal dementia (FTD). We report the frequency of tau mutations in a large population-based study of FTD carried out in the Netherlands from January 1994 to June 1998. Thirty-seven patients had >/=1 first-degree relative with dementia. A mutation in the tau gene was found in 17.8% of the group of patients with FTD and in 43% of patients with FTD who also had a positive family history of FTD. Three distinct missense mutations (G272V, P301L, R406W) accounted for 15.6% of the mutations. These three missense mutations, and a single amino acid deletion (DeltaK280) that was detected in one patient, strongly reduce the ability of tau to promote microtubule assembly. We also found an intronic mutation at position +33 after exon 9, which is likely to affect the alternative splicing of tau. Tau mutations are responsible for a large proportion of familial FTD cases; however, there are also families with FTD in which no mutations in tau have been found, which indicates locus and/or allelic heterogeneity. The different tau mutations may result in disturbances in the interactions of the protein tau with microtubules, resulting in hyperphosphorylation of tau protein, assembly into filaments, and subsequent cell death.

Common variants at 7p21 are associated with frontotemporal lobar degeneration with TDP-43 inclusions

Frontotemporal lobar degeneration (FTLD) is the second most common cause of presenile dementia. The predominant neuropathology is FTLD with TAR DNA-binding protein (TDP-43) inclusions (FTLD-TDP). FTLD-TDP is frequently familial, resulting from mutations in GRN (which encodes progranulin). We assembled an international collaboration to identify susceptibility loci for FTLD-TDP through a genome-wide association study of 515 individuals with FTLD-TDP. We found that FTLD-TDP associates with multiple SNPs mapping to a single linkage disequilibrium block on 7p21 that contains TMEM106B. Three SNPs retained genome-wide significance following Bonferroni correction (top SNP rs1990622, P = 1.08 × 10−11; odds ratio, minor allele (C) 0.61, 95% CI 0.53–0.71). The association replicated in 89 FTLD-TDP cases (rs1990622; P = 2 × 10−4). TMEM106B variants may confer risk of FTLD-TDP by increasing TMEM106B expression. TMEM106B variants also contribute to genetic risk for FTLD-TDP in individuals with mutations in GRN. Our data implicate variants in TMEM106B as a strong risk factor for FTLD-TDP, suggesting an underlying pathogenic mechanism.

Progranulin functions as a neurotrophic factor to regulate neurite outgrowth and enhance neuronal survival

Recently, mutations in the progranulin (PGRN) gene were found to cause familial and apparently sporadic frontotemporal lobe dementia (FTLD). Moreover, missense changes in PGRN were identified in patients with motor neuron degeneration, a condition that is related to FTLD. Most mutations identified in patients with FTLD until now have been null mutations. However, it remains unknown whether PGRN protein levels are reduced in the central nervous system from such patients. The effects of PGRN on neurons also remain to be established. We report that PGRN levels are reduced in the cerebrospinal fluid from FTLD patients carrying a PGRN mutation. We observe that PGRN and GRN E (one of the proteolytic fragments of PGRN) promote neuronal survival and enhance neurite outgrowth in cultured neurons. These results demonstrate that PGRN/GRN is a neurotrophic factor with activities that may be involved in the development of the nervous system and in neurodegeneration.

Incidence of dementia: Does gender make a difference?

Several studies suggested that women are at higher risk of dementia than men. However, that was based on rather limited data. We investigated possible gender differences in the incidence of dementia, Alzheimers disease and vascular dementia, in the Rotterdam Study, a large population based prospective cohort study in the Netherlands of 7,046 persons aged 55 years and older, free of dementia at baseline. In 40,441 person-years of follow-up (mean 5.7 years) we identified 395 new cases of dementia (overall incidence: 9.8 per 1,000 person-years). Alzheimers disease was the most frequent subtype of dementia (293 cases; 7.2 per 1,000). Vascular dementia was diagnosed in 57 participants (1.5 per 1,000). Overall, dementia incidence was similar for men and women (rate ratio women versus men: 1.00, 95% CI: 0.80-1.24). However, after 90 years of age dementia incidence declined in men but not in women (rate ratio 2.61, 95% CI: 1.04-6.56), in particular for Alzheimers disease (rate ratio 5.79, 95% CI: 1.40-23.90). The overall incidence of vascular dementia was lower in women than in men (rate ratio 0.57, 95% CI: 0.34-0.97). This large population-based study suggests no gender differences in the incidence of dementia up to high age. After 90 years of age the incidence of Alzheimers disease is higher for women than for men. The incidence of vascular dementia is higher for men than for women in all age groups.

A Mutation in the Fibroblast Growth Factor 14 Gene Is Associated with Autosomal Dominant Cerebral Ataxia

Hereditary spinocerebellar ataxias (SCAs) are a clinically and genetically heterogeneous group of neurodegenerative disorders for which ⩾14 different genetic loci have been identified. In some SCA types, expanded tri- or pentanucleotide repeats have been identified, and the length of these expansions correlates with the age at onset and with the severity of the clinical phenotype. In several other SCA types, no genetic defect has yet been identified. We describe a large, three-generation family with early-onset tremor, dyskinesia, and slowly progressive cerebellar ataxia, not associated with any of the known SCA loci, and a mutation in the fibroblast growth factor 14 (FGF14) gene on chromosome 13q34. Our observations are in accordance with the occurrence of ataxia and paroxysmal dyskinesia in Fgf14-knockout mice. As indicated by protein modeling, the amino acid change from phenylalanine to serine at position 145 is predicted to reduce the stability of the protein. The present FGF14 mutation represents a novel gene defect involved in the neurodegeneration of cerebellum and basal ganglia.

The clinical and pathological phenotype of C9ORF72 hexanucleotide repeat expansions.

There is increasing evidence that frontotemporal dementia and amyotrophic lateral sclerosis are part of a disease continuum. Recently, a hexanucleotide repeat expansion in C9orf72 was identified as a major cause of both sporadic and familial frontotemporal dementia and amyotrophic lateral sclerosis. The aim of this study was to investigate clinical and neuropathological characteristics of hexanucleotide repeat expansions in C9orf72 in a large cohort of Dutch patients with frontotemporal dementia. Repeat expansions were successfully determined in a cohort of 353 patients with sporadic or familial frontotemporal dementia with or without amyotrophic lateral sclerosis, and 522 neurologically normal controls. Immunohistochemistry was performed in a series of 10 brains from patients carrying expanded repeats using a panel of antibodies. In addition, the presence of RNA containing GGGGCC repeats in paraffin-embedded sections of post-mortem brain tissue was investigated using fluorescence in situ hybridization with a locked nucleic acid probe targeting the GGGGCC repeat. Hexanucleotide repeat expansions in C9orf72 were found in 37 patients with familial (28.7%) and five with sporadic frontotemporal dementia (2.2%). The mean age at onset was 56.9 ± 8.3 years (range 39-76), and disease duration 7.6 ± 4.6 years (range 1-22). The clinical phenotype of these patients varied between the behavioural variant of frontotemporal dementia (n = 34) and primary progressive aphasia (n = 8), with concomitant amyotrophic lateral sclerosis in seven patients. Predominant temporal atrophy on neuroimaging was present in 13 of 32 patients. Pathological examination of the 10 brains from patients carrying expanded repeats revealed frontotemporal lobar degeneration with neuronal transactive response DNA binding protein-positive inclusions of variable type, size and morphology in all brains. Fluorescence in situ hybridization analysis of brain material from patients with the repeat expansion, a microtubule-associated protein tau or a progranulin mutation, and controls did not show RNA-positive inclusions specific for brains with the GGGGCC repeat expansion. The hexanucleotide repeat expansion in C9orf72 is an important cause of frontotemporal dementia with and without amyotrophic lateral sclerosis, and is sometimes associated with primary progressive aphasia. Neuropathological hallmarks include neuronal and glial inclusions, and dystrophic neurites containing transactive response DNA binding protein. Future studies are needed to explain the wide variation in clinical presentation.