Predicting future rates of tau accumulation on PET

Clinical trials with anti-tau drugs will need to target individuals at risk of accumulating tau. Our objective was to identify variables available in a research setting that predict future rates of tau PET accumulation separately among individuals who were either cognitively unimpaired or cognitively impaired. All 337 participants had: a baseline study visit with MRI, amyloid PET, and tau PET exams, at least one follow-up tau PET exam; and met clinical criteria for membership in one of two clinical diagnostic groups: cognitively unimpaired (n = 203); or cognitively impaired (n = 134, a combined group of participants with either mild cognitive impairment or dementia with Alzheimer’s clinical syndrome). Our primary analyses were in these two clinical groups; however, we also evaluated subgroups dividing the unimpaired group by normal/abnormal amyloid PET and the impaired group by clinical phenotype (mild cognitive impairment, amnestic dementia, and non-amnestic dementia). Linear mixed effects models were used to estimate associations between age, sex, education, APOE genotype, amyloid and tau PET standardized uptake value ratio (SUVR), cognitive performance, cortical thickness, and white matter hyperintensity volume at baseline, and the rate of subsequent tau PET accumulation. Log-transformed tau PET SUVR was used as the response and rates were summarized as annual per cent change. A temporal lobe tau PET meta-region of interest was used. In the cognitively unimpaired group, only higher baseline amyloid PET was a significant independent predictor of higher tau accumulation rates (P < 0.001). Higher rates of tau accumulation were associated with faster rates of cognitive decline in the cognitively unimpaired subgroup with abnormal amyloid PET (P = 0.03), but among the subgroup with normal amyloid PET. In the cognitively impaired group, younger age (P = 0.02), higher baseline amyloid PET (P = 0.05), APOE ε4 (P = 0.05), and better cognitive performance (P = 0.05) were significant independent predictors of higher tau accumulation rates. Among impaired individuals, faster cognitive decline was associated with faster rates of tau accumulation (P = 0.01). While we examined many possible predictor variables, our results indicate that screening of unimpaired individuals for potential inclusion in anti-tau trials may be straightforward because the only independent predictor of high tau rates was amyloidosis. In cognitively impaired individuals, imaging and clinical variables consistent with early onset Alzheimer’s disease phenotype were associated with higher rates of tau PET accumulation suggesting this may be a highly advantageous group in which to conduct proof-of-concept clinical trials that target tau-related mechanisms. The nature of the dementia phenotype (amnestic versus non-amnestic) did not affect this conclusion.

Rare Tauopathies

Tauopathies are rare neurodegenerative disorders related to microtubule-associated protein tau, which functions to stabilize microtubules. Pathological changes caused by overexpression or hyperphosphorylation of tau lead to the disengagement of tau from microtubules and accumulation of toxic intracellular inclusions. Tau pathology is the underlying mechanism for several sporadic and genetic disorders. These are collectively known as tauopathies. Each tauopathy is differentiated from others by its neuropathological features such as the presence of specific isoforms of tau, type of cellular inclusions, and the regions of the brain affected. Neuropathological features, with a few exceptions however, do not correspond to distinct clinical phenotypes. There is considerable phenotypic overlap between the different tauopathies. Interaction between tau and other protein inclusions further alters the clinical phenotype.Recent advances in the development of tau biomarkers, especially the development of tau radioligands used in positron emission tomography neuroimaging, and a better understanding of biology and pathology of tau are important first steps toward the ultimate goal of accurate diagnosis and disease modification in tauopathies.

High School Football and Late-Life Risk of Neurodegenerative Syndromes, 1956-1970

OBJECTIVE

To assess whether athletes who played American varsity high school football between 1956 and 1970 have an increased risk of neurodegenerative diseases later in life.

PATIENTS AND METHODS

We identified all male varsity football players between 1956 and 1970 in the public high schools of Rochester, Minnesota, and non-football-playing male varsity swimmers, wrestlers, and basketball players. Using the medical records linkage system of the Rochester Epidemiology Project, we ascertained the incidence of late-life neurodegenerative diseases: dementia, parkinsonism, and amyotrophic lateral sclerosis. We also recorded medical record-documented head trauma during high school years.

RESULTS

We identified 296 varsity football players and 190 athletes engaging in other sports. Football players had an increased risk of medically documented head trauma, especially if they played football for more than 1 year. Compared with nonfootball athletes, football players did not have an increased risk of neurodegenerative disease overall or of the individual conditions of dementia, parkinsonism, and amyotrophic lateral sclerosis.

CONCLUSION

In this community-based study, varsity high school football players from 1956 to 1970 did not have an increased risk of neurodegenerative diseases compared with athletes engaged in other varsity sports. This was from an era when there was a generally nihilistic view of concussion dangers, less protective equipment, and no prohibition of spearing (head-first tackling). However, the size and strength of players from previous eras may not be comparable with that of current high school athletes.

The Apraxia of Speech Rating Scale: a tool for diagnosis and description of apraxia of speech

The purpose of this report is to describe an initial version of the Apraxia of Speech Rating Scale (ASRS), a scale designed to quantify the presence or absence, relative frequency, and severity of characteristics frequently associated with apraxia of speech (AOS). In this paper we report intra-judge and inter-judge reliability, as well as indices of validity, for the ASRS which was completed for 133 adult participants with a neurodegenerative speech or language disorder, 56 of whom had AOS. The overall inter-judge ICC among three clinicians was 0.94 for the total ASRS score and 0.91 for the number of AOS characteristics identified as present. Intra-judge ICC measures were high, ranging from 0.91 to 0.98. Validity was demonstrated on the basis of strong correlations with independent clinical diagnosis, as well as strong correlations of ASRS scores with independent clinical judgments of AOS severity. Results suggest that the ASRS is a potentially useful tool for documenting the presence and severity of characteristics of AOS. At this point in its development it has good potential for broader clinical use and for better subject description in AOS research.

LEARNING OUTCOMES

The Apraxia of Speech Rating Scale: A new tool for diagnosis and description of apraxia of speech 1. The reader will be able to explain characteristics of apraxia of speech. 2. The reader will be able to demonstrate use of a rating scale to document the presence and severity of speech characteristics. 3. The reader will be able to explain the reliability and validity of the ASRS.

Sensory ataxic neuropathy with ophthalmoparesis caused by POLG mutations

Mutations in POLG gene are responsible for a wide spectrum of clinical disorders with altered mitochondrial DNA (mtDNA) integrity, including mtDNA multiple deletions and depletion. Sensory ataxic neuropathy with ophthalmoparesis (SANDO) caused by mutations in POLG gene, fulfilling the clinical triad of sensory ataxic neuropathy, dysarthria and/or dysphagia and ophthalmoparesis, has described in a few reports. Here we described five cases of adult onset autosomal recessive sensory ataxic neuropathy with ophthalmoplegia. All patients had ataxia, neuropathy, myopathy, and progressive external ophthalmoplegia (PEO). The muscle pathology revealed ragged-red and cytochrome c oxidase (COX) negative fibers in three patients. However, deficiencies in the activities of mitochondrial respiratory chain enzyme complexes were not detected in any of the patients' muscle samples. Multiple deletions of mtDNA were detected in blood and muscle specimens but mtDNA depletion was not found. Due to these diagnostic difficulties, POLG-related syndromes are definitively diagnosed based on the presence of deleterious mutations in the POLG gene.

Phenotypic variability associated with progranulin haploinsufficiency in patients with the common 1477C-->T (Arg493X) mutation: an international initiative

BACKGROUND

The progranulin gene (GRN) is mutated in 5-10% of patients with frontotemporal lobar degeneration (FTLD) and in about 20% of patients with familial FTLD. The most common mutation in GRN is Arg493X. We aimed to establish the contribution of this mutation to FTLD and related disorders.

METHODS

We measured the frequency of Arg493X in 3405 unrelated patients with various neurodegenerative diseases using Taqman single-nucleotide polymorphism (SNP) genotyping. Clinicopathological characterisation and shared haplotype analysis were done for 30 families with FTLD who carry Arg493X. To investigate the effect of potential modifying loci, we did linear regression analyses with onset age as the covariate for GRN variants, for genotypes of the apolipoprotein E gene (APOE), and for haplotypes of the microtubule-associated protein tau gene (MAPT).

FINDINGS

Of 731 patients with FTLD, 16 (2%) carried Arg493X. This mutation was not detected in 2674 patients who did not have FTLD. In 37 patients with Arg493X from 30 families with FTLD, clinical diagnoses included frontotemporal dementia, primary progressive aphasia, corticobasal syndrome, and Alzheimer's disease. Range of onset age was 44-69 years. In all patients who came to autopsy (n=13), the pathological diagnosis was FTLD with neuronal inclusions that contained TAR DNA-binding protein or ubiquitin, but not tau. Neurofibrillary tangle pathology in the form of Braak staging correlated with overall neuropathology in the Arg493X carriers. Haplotype analyses suggested that Arg493X arose twice, with a single founder for 27 families. Linear regression analyses suggested that patients with SNP rs9897528 on their wild-type GRN allele have delayed symptom onset. Onset ages were not associated with the MAPT H1 or H2 haplotypes or APOE genotypes, but early memory deficits were associated with the presence of an APOE epsilon4 allele.

INTERPRETATION

Clinical heterogeneity is associated with GRN haploinsufficiency, and genetic variability on the wild-type GRN allele might have a role in the age-related disease penetrance of GRN mutations.

Mutations in progranulin are a major cause of ubiquitin-positive frontotemporal lobar degeneration

Null mutations in the progranulin gene (PGRN) were recently reported to cause tau-negative frontotemporal dementia linked to chromosome 17. We assessed the genetic contribution of PGRN mutations in an extended population of patients with frontotemporal lobar degeneration (FTLD) (N=378). Mutations were identified in 10% of the total FTLD population and 23% of patients with a positive family history. This mutation frequency dropped to 5% when analysis was restricted to an unbiased FTLD subpopulation (N=167) derived from patients referred to Alzheimer's Disease Research Centers (ADRC). Among the ADRC patients, PGRN mutations were equally frequent as mutations in the tau gene (MAPT). We identified 23 different pathogenic PGRN mutations, including a total of 21 nonsense, frameshift and splice-site mutations that cause premature termination of the coding sequence and degradation of the mutant RNA by nonsense-mediated decay. We also observed an unusual splice-site mutation in the exon 1 5' splice site, which leads to loss of the Kozac sequence, and a missense mutation in the hydrophobic core of the PGRN signal peptide. Both mutations revealed novel mechanisms that result in loss of functional PGRN. One mutation, c.1477C>T (p.Arg493X), was detected in eight independently ascertained familial FTLD patients who were shown to share a common extended haplotype over the PGRN genomic region. Clinical examination of patients with PGRN mutations revealed highly variable onset ages with language dysfunction as a common presenting symptom. Neuropathological examination showed FTLD with ubiquitin-positive cytoplasmic and intranuclear inclusions in all PGRN mutation carriers.

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.