Ashley Cannon

Mutations in progranulin cause tau-negative frontotemporal dementia linked to chromosome 17.

Frontotemporal dementia (FTD) is the second most common cause of dementia in people under the age of 65 years. A large proportion of FTD patients (35–50%) have a family history of dementia, consistent with a strong genetic component to the disease. In 1998, mutations in the gene encoding the microtubule-associated protein tau (MAPT) were shown to cause familial FTD with parkinsonism linked to chromosome 17q21 (FTDP-17). The neuropathology of patients with defined MAPT mutations is characterized by cytoplasmic neurofibrillary inclusions composed of hyperphosphorylated tau. However, in multiple FTD families with significant evidence for linkage to the same region on chromosome 17q21 (D17S1787–D17S806), mutations in MAPT have not been found and the patients consistently lack tau-immunoreactive inclusion pathology. In contrast, these patients have ubiquitin (ub)-immunoreactive neuronal cytoplasmic inclusions and characteristic lentiform ub-immunoreactive neuronal intranuclear inclusions. Here we demonstrate that in these families, FTD is caused by mutations in progranulin (PGRN) that are likely to create null alleles. PGRN is located 1.7 Mb centromeric of MAPT on chromosome 17q21.31 and encodes a 68.5-kDa secreted growth factor involved in the regulation of multiple processes including development, wound repair and inflammation. PGRN has also been strongly linked to tumorigenesis. Moreover, PGRN expression is increased in activated microglia in many neurodegenerative diseases including Creutzfeldt–Jakob disease, motor neuron disease and Alzheimers disease. Our results identify mutations in PGRN as a cause of neurodegenerative disease and indicate the importance of PGRN function for neuronal survival.

Clinicopathologic and 11C-Pittsburgh compound B implications of Thal amyloid phase across the Alzheimer’s disease spectrum

Murray et al. examine the correspondence between Thal amyloid phase, tau pathology and clinical characteristics in a large Alzheimer’s disease autopsy series. They extrapolate their findings to an autopsy cohort for which Pittsburgh compound-B imaging data are available, and evaluate the neuropathological significance of a quantitative amyloid-β imaging cut-off point.

APOE ε4 lowers age at onset and is a high risk factor for Alzheimer's disease; A case control study from central Norway

BackgroundThe objective of this study was to analyze factors influencing the risk and timing of Alzheimers disease (AD) in central Norway. The APOE ε4 allele is the only consistently identified risk factor for late onset Alzheimers disease (LOAD). We have described the allele frequencies of the apolipoprotein E gene (APOE) in a large population of patients with AD compared to the frequencies in a cognitively-normal control group, and estimated the effect of the APOE ε4 allele on the risk and the age at onset of AD in this population.Methods376 patients diagnosed with AD and 561 cognitively-normal control individuals with no known first degree relatives with dementia were genotyped for the APOE alleles. Allele frequencies and genotypes in patients and control individuals were compared. Odds Ratio for developing AD in different genotypes was calculated.ResultsOdds Ratio (OR) for developing AD was significantly increased in carriers of the APOE ε4 allele compared to individuals with the APOE ε3/ε3 genotype. Individuals carrying APOE ε4/ε4 had OR of 12.9 for developing AD, while carriers of APOE ε2/ε4 and APOE ε3/ε4 had OR of 3.2 and 4.2 respectively. The effect of the APOE ε4 allele was weaker with increasing age. Carrying the APOE ε2 allele showed no significant protective effect against AD and did not influence age at onset of the disease. Onset in LOAD patients was significantly reduced in a dose dependent manner from 78.4 years in patients without the APOE ε4 allele, to 75.3 in carriers of one APOE ε4 allele and 72.9 in carriers of two APOE ε4 alleles. Age at onset in early onset AD (EOAD) was not influenced by APOE ε4 alleles.ConclusionAPOE ε4 is a very strong risk factor for AD in the population of central Norway, and lowers age at onset of LOAD significantly.

Identification of a Novel Risk Locus for Progressive Supranuclear Palsy by a Pooled Genomewide Scan of 500,288 Single-Nucleotide Polymorphisms

To date, only the H1 MAPT haplotype has been consistently associated with risk of developing the neurodegenerative disease progressive supranuclear palsy (PSP). We hypothesized that additional genetic loci may be involved in conferring risk of PSP that could be identified through a pooling-based genomewide association study of >500,000 SNPs. Candidate SNPs with large differences in allelic frequency were identified by ranking all SNPs by their probe-intensity difference between cohorts. The MAPT H1 haplotype was strongly detected by this methodology, as was a second major locus on chromosome 11p12-p11 that showed evidence of association at allelic (P<.001), genotypic (P<.001), and haplotypic (P<.001) levels and was narrowed to a single haplotype block containing the DNA damage-binding protein 2 (DDB2) and lysosomal acid phosphatase 2 (ACP2) genes. Since DNA damage and lysosomal dysfunction have been implicated in aging and neurodegenerative processes, both genes are viable candidates for conferring risk of disease.

CHMP2B mutations are not a common cause of frontotemporal lobar degeneration

It was reported in 1995 that a large Danish family with familial frontotemporal dementia (FTD) was linked to the pericentromeric region of chromosome 3. It has since been claimed that a mutation in the splice acceptor site of exon 6 of CHMP2B is the pathogenic variant in this family. In order to determine whether CHMP2B mutations are a common cause of disease in patients with frontotemporal lobar degeneration (FTLD) we sequenced all exons and flanking regions of CHMP2B in 141 familial FTLD probands from the USA and UK. We failed to find a single pathogenic variant in any case. Polymorphisms were detected but were present in control samples. We conclude that mutations in CHMP2B are a rare cause of familial FTLD and may be specific to the Danish pedigree.

Study of a Swiss dopa-responsive dystonia family with a deletion in GCH1: Redefining DYT14 as DYT5

Objective: To report the study of a multigenerational Swiss family with dopa-responsive dystonia (DRD). Methods: Clinical investigation was made of available family members, including historical and chart reviews. Subject examinations were video recorded. Genetic analysis included a genome-wide linkage study with microsatellite markers (STR), GTP cyclohydrolase I (GCH1) gene sequencing, and dosage analysis. Results: We evaluated 32 individuals, of whom 6 were clinically diagnosed with DRD, with childhood-onset progressive foot dystonia, later generalizing, followed by parkinsonism in the two older patients. The response to levodopa was very good. Two additional patients had late onset dopa-responsive parkinsonism. Three other subjects had DRD symptoms on historical grounds. We found suggestive linkage to the previously reported DYT14 locus, which excluded GCH1. However, further study with more stringent criteria for disease status attribution showed linkage to a larger region, which included GCH1. No mutation was found in GCH1 by gene sequencing but dosage methods identified a novel heterozygous deletion of exons 3 to 6 of GCH1. The mutation was found in seven subjects. One of the patients with dystonia represented a phenocopy. Conclusions: This study rules out the previously reported DYT14 locus as a cause of disease, as a novel multiexonic deletion was identified in GCH1. This work highlights the necessity of an accurate clinical diagnosis in linkage studies as well as the need for appropriate allele frequencies, penetrance, and phenocopy estimates. Comprehensive sequencing and dosage analysis of known genes is recommended prior to genome-wide linkage analysis. GLOSSARY: DRD = dopa-responsive dystonia; GCH1 = GTP cyclohydrolase I; SNP = single nucleotide polymorphisms; STR = short tandem repeats.

Differential clinicopathologic and genetic features of late-onset amnestic dementias

Hippocampal sclerosis of the elderly (HpScl) and Alzheimer’s disease (AD), especially the limbic-predominant subtype (LP-AD), are amnestic syndromes that can be difficult to distinguish. To complicate matters, a subset has concomitant HpScl and AD (HpScl-AD). We examined a large cohort of autopsy-confirmed cases of HpScl, HpScl-AD, LP-AD, and typical AD to identify distinct clinical, genetic, and pathologic characteristics. HpScl cases were significantly older at death and had a substantially slower rate of cognitive decline than the AD subtypes. Genetic analysis revealed that the AD groups (AD, LP-AD, and HpScl–AD) were more likely to be APOE ε4 carriers. In contrast, the HpScl groups (HpScl and HpScl-AD) were more likely to exhibit genetic variants in GRN and TMEM106B that are associated with frontotemporal lobar degeneration. The HpScl groups had a high frequency of TDP-43 pathology that was most often Type A morphology and distribution, while typical AD and LP-AD had a significantly lower frequency of TDP-43 pathology that was most often Type B. These results suggest that HpScl and AD are pathologically and genetically distinct and non-synergistic neurodegenerative processes that present with amnestic dementia. Pure HpScl and HpScl with concomitant AD occur most often in elderly individuals.

Lrrk2 G2019S substitution in frontotemporal lobar degeneration with ubiquitin-immunoreactive neuronal inclusions

Leucine-rich repeat kinase 2 (LRRK2) mutation carriers can develop clinical symptoms other than typical parkinsonism such as dementia, amyotrophy or dystonia. To determine if LRRK2 mutations might be involved in frontotemporal dementia (FTD), 5 individuals with multiplex familial FTD kindreds and 41 pathologically confirmed cases of FTD, including 23 with a family history of dementia, were screened for genetic variations in the LRRK2 gene. We identified a LRRK2 mutation leading to the G2019S amino acid substitution in a 79-year-old woman with frontotemporal lobar degeneration with ubiquitinated neuronal intranuclear inclusions (FTLD-U/NII) and a possible family history of tremor. These findings may be coincidental; however, there is a small nucleus of LRRK2-positive patients displaying atypical features suggesting a role for this protein in other neurodegenerative disorders.

Risk-reducing effect of education in Alzheimer's disease

To estimate the effect of education on the risk of Alzheimers disease (AD).

Unbiased screen reveals ubiquilin-1 and -2 highly associated with huntingtin inclusions.

Recently mutations in ubiquilin-2 were identified in patients with amyotrophic lateral sclerosis (ALS) and ALS/dementia providing direct evidence for the importance of this protein in neurodegenerative diseases. Histological studies have suggested that ubiquilin-1/-2 are associated with various pathological inclusions including Lewy bodies in Parkinsons disease, neurofibrillary tangles in Alzheimers disease, polyQ inclusions in expansion repeat diseases and various proteinopathies associated with ALS and frontotemporal dementia. Using specific ubiquilin-2 antibodies and a series of transgenic mouse models of proteinopathies associated with neurodegenerative disease, we show that ubiquilin-2 preferentially associates with huntingtin polyQ expansion aggregates compared to α-synuclein, tau and several other types of protein inclusions. These results were confirmed by similar findings for ubiquilin-1 and -2 in human brain tissue sections, where accumulation was observed in huntingtin inclusions, but only infrequently in other types of protein inclusions. In cultured cells, ubiquilin-2 associates with huntingtin/polyQ aggregates, but this is not compromised by disease-causing mutations. Although ubiquilin proteins can function as chaperones to shuttle proteins for degradation, there is persistent co-localization between ubiquilin-2 and polyQ aggregated proteins during disease progression in the N586-82Q-C63 Huntingtons disease mouse model. Thus, the co-localization of ubiquilin-2 with the huntingtin aggregates does not appear to facilitate aggregate removal.