Neurodegeneration in frontotemporal lobar degeneration and motor neurone disease associated with expansions in C9orf72 is linked to TDP-43 pathology and not associated with aggregated forms of dipeptide repeat proteins

Aims

A hexanucleotide expansion in C9orf72 is the major genetic cause of inherited behavioural variant Frontotemporal dementia (bvFTD) and motor neurone disease (MND), although the pathological mechanism(s) underlying disease remains uncertain.

Methods

Using antibodies to poly‐GA, poly‐GP, poly‐GR, poly‐AP and poly‐PR proteins, we examined sections of cerebral cortex, hippocampus, thalamus, cerebellum and spinal cord, from 20 patients with bvFTD and/or MND bearing an expansion in C9orf72 for aggregated deposits of dipeptide repeat proteins (DPR).

Results

Antibodies to poly‐GA, poly‐GP and poly‐GR detected numerous rounded cytoplasmic inclusions (NCI) within granule cells of hippocampal dentate gyrus and those of the cerebellum, as well as ‘star‐burst’ shaped NCI in pyramidal neurones of CA3/4 region of hippocampus. NCI were uncommon in Purkinje cells, and only very rarely seen in anterior horn cells. Poly‐PA antibody detected occasional NCI within CA3/4 neurones alone, whereas poly‐PR antibody did not identify any NCI but immunostained the nucleus of anterior horn cells, CA3/4 neurones and Purkinje cells, in patients with or without expansion in C9orf72, as well as in normal controls. Poly‐GA antibody generally detected more DPR than poly‐GP, which in turn was greater than poly‐GR. All patients with bvFTD + MND or MND showed plentiful p62/TDP‐43 positive inclusions in remaining anterior horn cells.

Conclusion

Degeneration and loss of anterior horn cells associated with expansions in C9orf72 occurs in the absence of DPR, and implies that changes involving loss of nuclear staining for and a cytoplasmic aggregation of TDP‐43 are more likely to be the cause of this.

Corticobasal degeneration and progressive supranuclear palsy share a common tau haplotype

OBJECTIVE

To analyze the association of polymorphisms in the tau gene with pathologically confirmed corticobasal degeneration (CBD).

BACKGROUND

The authors previously described an extended tau haplotype (H1) that covers the human tau gene and is associated with the development of progressive supranuclear palsy (PSP). The authors now extend this analysis to CBD, a neurodegenerative condition with clinical and neuropathologic similarities to PSP. Like PSP, CBD is associated with accumulation of aggregates containing the 4-repeat isoforms of tau. Because of difficulty in diagnosis of CBD, the authors only analyzed cases with pathologically confirmed CBD.

METHODS

The authors collected 57 unrelated, neuropathologically confirmed cases of CBD. Tau sequencing in these cases failed to show the presence of pathogenic mutations. Polymorphisms that spanned the tau gene were analyzed in all CBD cases and controls.

RESULTS

Analyzing tau polymorphisms in CBD cases showed that the frequency of H1 and H1/H1 was significantly increased when analyzing all cases and when separating by country of origin. H1 frequency in all CBD cases was 0.921, compared with a control frequency of 0.766 (X(2) = 9.1, p = 0.00255 [1df], OR 3.56 [8.43 > CI 95% > 1.53]). The H1/H1 frequency was also significantly higher at 0.842 compared with 0.596 in age-matched controls (X(2) = 17.42, p = 0.00016, 2df), OR 3.61 [7.05 > CI 95% > 1.85]).

CONCLUSIONS

The CBD tau association described here suggests that PSP and CBD share a similar cause, although the pathogenic mechanism behind the two diseases leads to a different clinical and pathologic phenotype.

Clinical features of dementia associated with apolipoprotein epsilon4: discrimination with a neural network genetic algorithm

BACKGROUND

It is unclear whether the APOE epsilon4 allele is associated with distinct clinical features in dementia.

METHOD

100 cases meeting ICD criteria for dementia were interviewed using standardized instruments and genotyped for APOE. The presence of the epsilon4 allele was used by a genetic algorithm neural network (GANN) to discriminate symptoms and signs.

RESULTS

The GANN selected six features: gender, systolic blood pressure, absence of ankle tendon reflexes, history of weight loss, history of falls, and interviewer observed lability of mood. Using these features, a neural network discriminated cases according to epsilon4 highly accurately (area under receiver operating characteristic=0.83, sensitivity=0.78, specificity=0.78).

CONCLUSIONS

A GANN is able to discriminate a clinically distinct group of features among dementia patients who express the epsilon4 allele.

Pick's disease is associated with mutations in the tau gene

Recently, mutations within the tau gene have been associated with some familial forms of frontotemporal dementia. To investigate whether tau gene mutations are also associated with Pick's disease, we analyzed the tau gene in 30 cases of pathologically confirmed Pick's disease. Two coding mutations were identified in separate cases of Pick's disease. A glycine-to-arginine mutation at codon 389 was detected in 1 case and a lysine-to-threonine mutation at codon 257 was identified in another. Analysis of dephosphorylated tau from the brain of the patient with the codon 389 mutation revealed a prominent band representing tau, with four microtubule-binding domains and no amino terminal inserts. This is in contrast to Pick's disease without any tau gene mutations, which consist of tau with mainly three microtubule-binding domains and only a trace of tau, with four microtubule-binding domains. Functional analysis of tau with these two mutations demonstrated a reduced ability of tau to promote microtubule assembly. Surprisingly, these mutations increased tau's susceptibility to calpain I digestion, suggesting that this feature may be related to the formation of a Pick type of histology. Moreover, these data suggest that Pick's disease is not a separate entity but part of the frontotemporal dementia disease spectrum.

Detection of the interleukin 18 family in rat brain by RT-PCR

Interleukin 18, an inflammatory cytokine, mediates its effects by interaction with its receptor complex, consisting of the IL-18 receptor (IL-18R) and receptor accessory protein (AcPL). A functional inhibitor of IL-18, the IL-18 binding protein (IL-18BP), has been identified recently. This study reports the detection of IL-18, IL-18R, AcPL and IL-18BP mRNA expression in the brain of normal adult rats using RT-PCR.

Frequency of tau mutations in three series of non-Alzheimer's degenerative dementia

Splice-site and missense mutations have been identified in tau associated with frontotemporal dementia with parkinsonism linked to chromosome 17. In this study we assessed the genetic contribution of tau mutations to three patient series with non-Alzheimer's (non-AD) degenerative dementia. The groups included (1) a community-based dementia series from Minnesota, MN; (2) a referral series with clinicopathological tauopathy; and (3) a pathologically confirmed familial frontotemporal dementia series from Manchester, UK. Comparing the three clinical series: in the stringently diagnosed Manchester frontotemporal dementia series, tau mutations were present in 13.6% of cases (three splice-site mutations); in the clinicopathological referral series that used more general inclusion criteria, 3 cases with P301L mutations were observed, which represents a lower mutation frequency of 3.6% (9.4% in familial cases); in contrast, tau mutations were not detected in the Minnesota community-based dementia series, suggesting the occurrence of these mutations in dementia generally is rare (<0.2%). These data identify the prevalence of mutations in three different clinical settings and indicate that this figure is sensitive to the diagnostic criteria used in each patient series.

5' splice site mutations in tau associated with the inherited dementia FTDP-17 affect a stem-loop structure that regulates alternative splicing of exon 10

Missense and splice site mutations in the microtubule-associated protein tau gene were recently found associated with fronto-temporal dementia and parkinsonism linked to chromosome 17 (Poorkaj et al. (1998) Ann. Neurol. 43, 815-825; Hutton et al. (1998) Nature 393, 702-705; Spillantini et al. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 7737-7741). The mutations in the 5' splice site of exon 10 were shown to increase the ratio of tau mRNAs containing exon 10 and thus the proportion of Tau protein isoforms with 4 microtubule binding repeat domains, although how this increase leads to neurodegeneration is presently unclear. The mechanism by which these mutations increase tau exon 10 splicing was not determined, although the mutations were predicted to disrupt a potential stem-loop structure that was likely involved in the regulation of exon 10 alternative splicing. Here we describe in vitro splicing assays and RNA structural analysis that demonstrate that the mutations do indeed act through disruption of the stem-loop structure and that the stability of this secondary structure feature at least partially determines the ratio of tau exon 10+/- transcripts. In addition, we provide evidence that the stability of the stem-loop structure underlies the alternative splicing of this exon in other species.

Apolipoprotein E genotype does not affect the age of onset of dementia in families with defined tau mutations

We have assessed whether apolipoprotein E (ApoE) genotype influences the age of onset of dementia in a series of families with frontal temporal dementia with defined mutations in the tau gene. In contrast to the situation in Alzheimer's disease (AD), we could find no evidence that the age of onset of disease was influenced by the ApoE genotype.

Association of missense and 5'-splice-site mutations in tau with the inherited dementia FTDP-17

Thirteen families have been described with an autosomal dominantly inherited dementia named frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), historically termed Pick's disease. Most FTDP-17 cases show neuronal and/or glial inclusions that stain positively with antibodies raised against the microtubule-associated protein Tau, although the Tau pathology varies considerably in both its quantity (or severity) and characteristics. Previous studies have mapped the FTDP-17 locus to a 2-centimorgan region on chromosome 17q21.11; the tau gene also lies within this region. We have now sequenced tau in FTDP-17 families and identified three missense mutations (G272V, P301L and R406W) and three mutations in the 5' splice site of exon 10. The splice-site mutations all destabilize a potential stem-loop structure which is probably involved in regulating the alternative splicing of exon10. This causes more frequent usage of the 5' splice site and an increased proportion of tau transcripts that include exon 10. The increase in exon 10+ messenger RNA will increase the proportion of Tau containing four microtubule-binding repeats, which is consistent with the neuropathology described in several families with FTDP-17.

Effect of apolipoprotein E status on clinical features of dementia

OBJECTIVE

The aims of this study were (a) to determine the frequency of APOE genotypes in dementia, (b) to relate e4 allele frequency to clinical symptomatology of dementia and (c) to relate e4 and assess risk factors for different types of dementia.

DESIGN

Prospective clinical study setting older patients with dementia known to a community-based old age psychiatry service.

SAMPLE

101 patients fulfilling ICD 10 criteria for dementia.

RESULTS

Replication of previous findings of an association between APOE4 and Alzheimer's disease: younger age of onset of dementia; family history of dementia; persecutory ideation; and (retrospectively determined) rate of competent decline. No association was found between APOE4 and vascular dementia. The association between APOE4 and 'mixed dementia' was intermediate between that of pure Alzheimer's disease and pure vascular dementia.

CONCLUSION

The results confirm the relationship between clinical features of dementia and APOE4 status. It may be that APOE can be used as an adjunct to clinical diagnosis.

ApoE2 allele, Down's syndrome, and dementia

All individuals with Down's syndrome (trisomy 21-DS) develop the pathogenic hallmarks of Alzheimer's disease in old age (+40 years). The extent of pathology is variable, but it has been shown that the amount of beta-amyloid pathology is variable and related to age and the degree of dementia. Thus, in DS, growing old is associated with a progressive pathological process which results in cognitive decline. However, neuropsychological studies of older DS subjects have identified a clinical dementia in only a proportion of cases. These contradictory observations could be reconciled if some factor existed which modulated the rate and amount of beta-amyloid pathology. Recent studies demonstrate an association between the apolipoprotein E4 (ApoE4) allele and the earlier age of onset in both sporadic and familial AD. Increased amounts of beta-amyloid pathology can also be related to the E4 allele. However, at present there are no data documenting the effects of ApoE genotype on the expression or degree of clinical symptoms of the disease. We have examined the ApoE genotype in a cohort of clinically evaluated elderly patients with DS in order to examine the effects of ApoE genotype on the clinical symptoms of dementia. We report here that, despite the presence of an active disease process, the ApoE E2 allele is associated with longevity and preservation of cognitive functioning.

Apolipoprotein E epsilon 2 allele promotes longevity and protects patients with Down's syndrome from dementia

Although individuals with Down's syndrome nearly always develop the clinical and pathological features of Alzheimer's disease, some clearly do not become demented despite living into their sixth and seventh decades. Genetic variation at the apolipoprotein E locus has recently been shown to be an important determinant of Alzheimer's disease, with the epsilon 4 allele having been shown to be associated with the disease and, at least in some cases, the epsilon 2 allele being negatively associated with the disease. Here we show, in a series of clinically assessed individuals with Down's syndrome, that the epsilon 2 allele of ApoE is associated with both longevity and the absence of clinical evidence of dementia. These data show that the clinical phenotype of Down's syndrome can be modulated by genes on chromosomes other than chromosome 21. The importance of this observation to the pathogenesis of Alzheimer's disease, both in Down's syndrome and in general, is discussed.