Liisa Myllykangas

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.

Chromosome 9p21 in amyotrophic lateral sclerosis in Finland: a genome-wide association study

BACKGROUND The genetic cause of amyotrophic lateral sclerosis (ALS) is not well understood. Finland is a well suited location for a genome-wide association study of ALS because the incidence of the disease is one of the highest in the world, and because the genetic homogeneity of the Finnish population enhances the ability to detect risk loci. We aimed to identify genetic risk factors for ALS in the Finnish population. METHODS We did a genome-wide association study of Finnish patients with ALS and control individuals by use of Illumina genome-wide genotyping arrays. DNA was collected from patients who attended an ALS specialty clinic that receives referrals from neurologists throughout Finland. Control samples were from a population-based study of elderly Finnish individuals. Patients known to carry D90A alleles of the SOD1 gene (n=40) were included in the final analysis as positive controls to assess whether our genome-wide association study was able to detect an association signal at this locus. FINDINGS We obtained samples from 442 patients with ALS and 521 control individuals. After quality control filters were applied, 318 167 single nucleotide polymorphisms (SNPs) from 405 people with ALS and 497 control individuals were available for analysis. We identified two association peaks that exceeded genome-wide significance. One was located on chromosome 21q22 (rs13048019, p=2·58×10(-8)), which corresponds to the autosomal recessive D90A allele of the SOD1 gene. The other was detected in a 232 kb block of linkage disequilibrium (rs3849942, p=9·11×10(-11)) in a region of chromosome 9p that was previously identified in linkage studies of families with ALS. Within this region, we defined a 42-SNP haplotype that was associated with significantly increased risk of ALS (p=7·47×10(-33) when people with familial ALS were compared with controls, odds ratio 21·0, 95% CI 11·2-39·1) and which overlapped with an association locus recently reported for frontotemporal dementia. For the 93 patients with familial ALS, the population attributable risk for the chromosome 9p21 locus was 37·9% (95% CI 27·7-48·1) and that for D90A homozygosity was 25·5% (16·9-34·1). INTERPRETATION The chromosome 9p21 locus is a major cause of familial ALS in the Finnish population. Our data suggest the presence of a founder mutation for chromosome 9p21-linked ALS. Furthermore, the overlap with the risk haplotype recently reported for frontotemporal dementia provides further evidence of a shared genetic cause for these two neurodegenerative diseases. FUNDING National Institutes of Health and National Institute on Aging, Microsoft Research, ALS Association, Helsinki University Central Hospital, Finnish Academy, Finnish Medical Society Duodecim, and Kuopio University.

Aggregated α-Synuclein Mediates Dopaminergic Neurotoxicity In Vivo

Mutations in the synaptic protein α-synuclein cause rare genetic forms of Parkinsons disease. α-Synuclein is thought to play a critical role in more common sporadic cases of Parkinsons disease as well because the protein aggregates in the hallmark intraneuronal inclusions of the disorder, Lewy bodies. To test the role of protein aggregation in the pathogenesis of Parkinsons disease, we expressed a form of α-synuclein with a deletion of amino acids 71–82 that is unable to aggregate in vitro in a transgenic Drosophila model of the disorder. We found no evidence of large aggregates or oligomeric species of α-synuclein in these animals and no loss of tyrosine hydroxylase-positive neurons. We also expressed a truncated form of α-synuclein that has enhanced ability to aggregate in vitro. This truncated form of α-synuclein showed increased aggregation into large inclusions bodies, increased accumulation of high molecular weight α-synuclein species, and demonstrated enhanced neurotoxicity in vivo. Our findings thus support a critical role for aggregation of α-synuclein in mediating toxicity to dopaminergic neurons in vivo, although the precise role each aggregated form of α-synuclein plays in neurotoxicity remains to be determined.

A novel α-synuclein mutation A53E associated with atypical multiple system atrophy and Parkinson's disease-type pathology

We describe the clinical, neuropathological, and genetic features of a Finnish patient with a novel α-synuclein (SNCA) mutation A53E. The patient was clinically diagnosed with atypical Parkinsons disease (PD) with age of onset at 36 years. In the neuropathological analysis performed at the age of 60 years, highly abundant SNCA pathology was observed throughout the brain and spinal cord showing features of multiple system atrophy and PD. Neuronal and glial (including oligodendroglial) SNCA inclusions and neurites were found to be particularly prominent in the putamen, caudatus, amygdala, temporal and insular cortices, gyrus cinguli, and hippocampus CA2-3 region. These areas as well as the substantia nigra and locus coeruleus showed neuronal loss and gliosis. We also found TDP-43 positive but mostly SNCA negative perinuclear inclusions in the dentate fascia of the hippocampus. The A53E mutation was found in 2 other relatives who had parkinsonism. Our results suggest that the novel SNCA A53E substitution is a causative mutation resulting clinically in parkinsonism and pathologically in severe multiple system atrophy- and PD-type phenotype.

Prevalence of Alzheimer’s disease in very elderly people: A prospective neuropathological study

Background: No previous autopsy-controlled, prospective, and population-based studies are available on the prevalence of AD in very elderly people. Objective: To study the point prevalence of neuropathologically defined AD in a population of people at least 85 years of age, stratified according to their APOE genotype. Methods: A population-based sample of 532 (of a total population of 601) elderly Finnish individuals, aged 85 years or more, were clinically tested for dementia in 1991 (with follow-up studies of the survivors in 1994, 1996, and 1999) and genotyped for APOE. An autopsy involving neuropathologic diagnosis of AD according to modified consensus criteria was performed in 118 of 198 deceased subjects who had been demented on April 1, 1991, and in 62 of 201 nondemented individuals. Results: The prevalence of neuropathologically defined AD was 33%, whereas the prevalence of clinically diagnosed AD was 16%. There was a highly significant (p < 0.001) association between the APOE ε4 allele and AD: Sixty-three percent of APOE ε4 carriers and 20% of noncarriers had neuropathologic AD. The respective figures in subjects aged 90 years or more were 71 and 22%. Conclusions: The prevalence of neuropathologically defined AD is higher than that reported in most previous studies based on clinical diagnosis. The discrepancy between the neuropathologic and clinical diagnoses of AD in very elderly subjects may affect the results of population-based studies. The APOE genotype has a strong effect on the prevalence of neuropathologically defined AD, even after 90 years of age.

Senile systemic amyloidosis affects 25% of the very aged and associates with genetic variation in alpha2-macroglobulin and tau: a population-based autopsy study.

Background. Senile systemic amyloidosis (SSA) is characterized by deposition of wild‐type transthyretin (TTR)‐based amyloid in parenchymal organs in elderly individuals. Previously, no population‐based studies have been performed on SSA. Methods. Here we have studied the prevalence and risk factors for SSA in a Finnish autopsied population aged 85 or over, as part of the population‐based Vantaa 85+ Autopsy Study (n = 256). The diagnosis of SSA was based on histological examination of myocardial samples stained with Congo red and anti‐TTR immunohistochemistry. The genotype frequencies of 20 polymorphisms in 9 genes in subjects with and without SSA were compared. Results. The prevalence of SSA was 25%. SSA was associated with age, myocardial infarctions, the G/G (Val/Val) genotype of the exon 24 polymorphism in the alpha2‐macroglobulin (α2M), and the H2 haplotype of the tau gene (P‐values 0.002, 0.004, 0.042, and 0.016). Conclusion. This population‐based study shows that SSA is very common in old individuals, affecting one‐quarter of people aged over 85 years. Myocardial infarctions and variation in the genes for α2M and tau may be associated with SSA.

The chromosome 9 ALS and FTD locus is probably derived from a single founder

We and others have recently reported an association between amyotrophic lateral sclerosis (ALS) and single nucleotide polymorphisms on chromosome 9p21 in several populations. Here we show that the associated haplotype is the same in all populations and that several families previously shown to have genetic linkage to this region also share this haplotype. The most parsimonious explanation of these data are that there is a single founder for this form of disease.

Plasma homocysteine, Alzheimer and cerebrovascular pathology: a population-based autopsy study.

Elevated plasma total homocysteine is associated with increased risk of dementia/Alzheimers disease, but underlying pathophysiological mechanisms are not fully understood. This study investigated possible links between baseline homocysteine, and post-mortem neuropathological and magnetic resonance imaging findings up to 10 years later in the Vantaa 85+ population including people aged ≥85 years. Two hundred and sixty-five individuals had homocysteine and autopsy data, of which 103 had post-mortem brain magnetic resonance imaging scans. Methenamine silver staining was used for amyloid-β and modified Bielschowsky method for neurofibrillary tangles and neuritic plaques. Macroscopic infarcts were identified from cerebral hemispheres, brainstem and cerebellum slices. Standardized methods were used to determine microscopic infarcts, cerebral amyoloid angiopathy, and α-synuclein pathology. Magnetic resonance imaging was used for visual ratings of the degree of medial temporal lobe atrophy, and periventricular and deep white matter hyperintensities. Elevated baseline homocysteine was associated with increased neurofibrillary tangles count at the time of death: for the highest homocysteine quartile, odds ratio (95% confidence interval) was 2.60 (1.28-5.28). The association was observed particularly in people with dementia, in the presence of cerebral infarcts, and with longer time between the baseline homocysteine assessment and death. Also, elevated homocysteine tended to relate to amyloid-β accumulation, but this was seen only with longer baseline-death interval: odds ratio (95% confidence interval) was 2.52 (0.88-7.19) for the highest homocysteine quartile. On post-mortem magnetic resonance imaging, for the highest homocysteine quartile odds ratio (95% confidence interval) was 3.78 (1.12-12.79) for more severe medial temporal atrophy and 4.69 (1.14-19.33) for more severe periventricular white matter hyperintensities. All associations were independent of several potential confounders, including common vascular risk factors. No relationships between homocysteine and cerebral macro- or microinfarcts, cerebral amyoloid angiopathy or α-synuclein pathology were detected. These results suggest that elevated homocysteine in adults aged ≥85 years may contribute to increased Alzheimer-type pathology, particularly neurofibrillary tangles burden. This effect seems to be more pronounced in the presence of cerebrovascular pathology. Randomized controlled trials are needed to determine the impact of homocysteine-lowering treatments on dementia-related pathology.

CADASIL and CARASIL

CADASIL and CARASIL are hereditary small vessel diseases leading to vascular dementia. CADASIL commonly begins with migraine followed by minor strokes in mid‐adulthood. Dominantly inherited CADASIL is caused by mutations (n > 230) in NOTCH3 gene, which encodes Notch3 receptor expressed in vascular smooth muscle cells (VSMC). Notch3 extracellular domain (N3ECD) accumulates in arterial walls followed by VSMC degeneration and subsequent fibrosis and stenosis of arterioles, predominantly in cerebral white matter, where characteristic ischemic MRI changes and lacunar infarcts emerge. The likely pathogenesis of CADASIL is toxic gain of function related to mutation‐induced unpaired cysteine in N3ECD. Definite diagnosis is made by molecular genetics but is also possible by electron microscopic demonstration of pathognomonic granular osmiophilic material at VSMCs or by positive immunohistochemistry for N3ECD in dermal arteries.

Neuropathologic Findings of Dementia with Lewy Bodies (DLB) in a Population-based Vantaa 85+ Study

The consortium on dementia with Lewy bodies has established consensus guidelines for the neuropathologic diagnosis of dementia with Lewy bodies (DLB) including the likelihood that the neuropathologic findings associate with the clinical syndrome. Nevertheless, clinico-pathological correlations remain controversial. We applied the consensus guidelines for determining Lewy-related pathology (LRP) and evaluated the clinical presentation in the prospective, population-based Vantaa 85+ study consisting of individuals at least 85 years of age. LRP was seen in 36% of 304 subjects and categorized as follows: 3% brainstem-predominant, 14% limbic, 15% diffuse neocortical type (4% could not be categorized). The likelihood that the neuropathology predicts the DLB clinical syndrome was low in 6%, intermediate in 13%, and high in 13% of all 304 subjects. In the latter two groups, 77% were demented, 35% had at least one extrapyramidal symptom, and 15% had visual hallucinations. Surprisingly, DLB clinical features associated better with high neurofibrillary stage than with diffuse neocortical LRP. Moreover, the neurofibrillary stage, substantia nigra neuron loss, and grade of Lewy neurites in hippocampal CA2-3 region, each showed a significant association with the extent of LRP. In conclusion, the neuropathologic DLB in this very elderly population was common, but the clinical symptoms tended to associate better with severe neurofibrillary pathology than with extensive LRP.