Ainhoa Alzualde

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.

Genetic and Clinical Features of Progranulin-Associated Frontotemporal Lobar Degeneration

OBJECTIVE To assess the relative frequency of unique mutations and their associated characteristics in 97 individuals with mutations in progranulin (GRN), an important cause of frontotemporal lobar degeneration (FTLD). PARTICIPANTS AND DESIGN A 46-site International Frontotemporal Lobar Degeneration Collaboration was formed to collect cases of FTLD with TAR DNA-binding protein of 43-kDa (TDP-43)-positive inclusions (FTLD-TDP). We identified 97 individuals with FTLD-TDP with pathogenic GRN mutations (GRN+ FTLD-TDP), assessed their genetic and clinical characteristics, and compared them with 453 patients with FTLD-TDP in which GRN mutations were excluded (GRN- FTLD-TDP). No patients were known to be related. Neuropathologic characteristics were confirmed as FTLD-TDP in 79 of the 97 GRN+ FTLD-TDP cases and all of the GRN- FTLD-TDP cases. RESULTS Age at onset of FTLD was younger in patients with GRN+ FTLD-TDP vs GRN- FTLD-TDP (median, 58.0 vs 61.0 years; P < .001), as was age at death (median, 65.5 vs 69.0 years; P < .001). Concomitant motor neuron disease was much less common in GRN+ FTLD-TDP vs GRN- FTLD-TDP (5.4% vs 26.3%; P < .001). Fifty different GRN mutations were observed, including 2 novel mutations: c.139delG (p.D47TfsX7) and c.378C>A (p.C126X). The 2 most common GRN mutations were c.1477C>T (p.R493X, found in 18 patients, representing 18.6% of GRN cases) and c.26C>A (p.A9D, found in 6 patients, representing 6.2% of cases). Patients with the c.1477C>T mutation shared a haplotype on chromosome 17; clinically, they resembled patients with other GRN mutations. Patients with the c.26C>A mutation appeared to have a younger age at onset of FTLD and at death and more parkinsonian features than those with other GRN mutations. CONCLUSION GRN+ FTLD-TDP differs in key features from GRN- FTLD-TDP.

LRRK2 G2019S and R1441G mutations associated with Parkinson’s disease are common in the Basque Country, but relative prevalence is determined by ethnicity

Mutations in LRRK2 gene are the most frequent cause of Parkinson’s disease (PD) described, but their prevalence varies between populations. Patients, 418, with PD and 138 unrelated controls from the Basque Country were screened for LRRK2 G2019S and R1441G mutations. Of the patients, 3.82% were heterozygous carriers of G2019S and 13.15% of R1441G. G2019S frequency was higher in non-Basque population (6.0%), while R1441G was more common in Basque origin population (22.4%). Our conclusion is that both G2019S and R1441G mutations’ frequency varies markedly between Basque and non-Basque origin population reinforcing the importance of ethnicity consideration when establishing mutation prevalence.

Mutations in Progranulin Gene: Clinical, Pathological, and Ribonucleic Acid Expression Findings

BACKGROUND There is an increasing interest in the clinico-pathological correlation of mutations in progranulin (PGRN) and frontotemporal lobar degeneration (FTLD) complex diseases. We aim to study the PGRN expression variability in patients with different clinical features for a better understanding of its roles in FTLD disease. METHODS We sequenced the PGRN gene in 72 patients suffering from FTLD (25 familial and 47 sporadic cases) and in 24 asymptomatic at-risk relatives. We also analyzed PGRN expression in blood by quantitative real-time polymerase chain reaction from 37 patients, 8 asymptomatic mutation carriers, and 10 control subjects as well as in brain tissue from 16 patients and 9 control subjects. RESULTS Four novel mutations were associated with familial and sporadic FTLD and familial dementia associated with amyotrophic lateral sclerosis. We identified a close association between the IVS6-1G>A mutation in PGRN and corticobasal syndrome. Brain tissue was available for carriers of two of the four mutations (IVS6-1 G>A and P357HfsX3). Immunohistochemical analysis revealed ubiquitin- and TDP-43positive and tau/alpha-synuclein negative immunoreactive neuronal intranuclear inclusions. The relative expression of PGRN in the clinical sample was significantly lower in carriers of the IVS6-1 G>A than in control subjects. CONCLUSIONS Progranulopathies are a major cause of the main phenotypes included in the FTLD complex. According to our results, the level of expression of PGRN in blood could be a useful marker both for diagnostics of part of the spectrum of FTLD conditions and for monitoring future treatments that might boost the level of PGRN in this disorder.

Olfactory deficits and cardiac 123I‐MIBG in Parkinson's disease related to the LRRK2 R1441G and G2019S mutations

It has been proposed that olfactory tests and metaiodobenzylguanidine cardiac scintigraphy may help diagnose idiopathic Parkinsons disease in the premotor phase. However, it is not clear what value these tests have in all patients with Parkinsons disease and, particularly, in those who carry mutations in LRRK2. The objective was to analyze olfactory dysfunction and the changes in cardiac I‐metaiodobenzylguanidine uptake in patients with Parkinsons disease carrying the R1441G and G2019S mutations in LRRK2, and in patients with Parkinsons disease with no known mutations. Patients with Parkinsons disease were screened for R1441G and G2019S LRRK2 gene mutations and classified as LRRK2 mutation carriers or noncarriers. A total of 190 patients with Parkinsons disease (44 LRRK2 mutation carriers) were tested for olfactory dysfunction using the Brief Smell Identification Test. Cardiac 123I‐metaiodobenzylguanidine scintigraphy was performed on 90 patients with Parkinsons disease (27 LRRK2 mutation carriers). Thirty‐six percent of patients with LRRK2 mutations have hyposmia, compared to 75% of noncarrier patients with Parkinsons disease (P < .001). Sixty‐six percent of LRRK2 mutation carriers have low early metaiodobenzylguanidine uptake, compared to 86% of noncarriers (P = .048). Similarly, the heart/mediastinum ratio in delayed metaiodobenzylguanidine images appeared to differ between these groups of patients with Parkinsons disease, although these results did not reach statistical significance. The data obtained indicate that olfactory and cardiac impairment is less prevalent when Parkinsons disease is associated with mutations in LRRK2, although the underlying mechanisms for this difference remain unclear. Thus, such screening would be less useful to detect the premotor phase in asymptomatic relatives who carry mutations in LRRK2 than in cases not associated with LRRK2.

A Novel PRNP Y218N Mutation in Gerstmann-Straussler-Scheinker Disease With Neurofibrillary Degeneration

Gerstmann-Sträussler-Scheinker (GSS) disease is a prion disease associated with prion protein gene (PRNP) mutations. We report a novel PRNP mutation (Y218N) associated with GSS disease in a pathologically confirmed case and in two other affected family members. The clinical features of these cases met criteria for possible Alzheimer disease and possible frontotemporal dementia. Neuropathologic analysis revealed deposition of proteinase K-resistant prion protein (PrPres), widespread hyperphosphorylated tau pathology, abnormal accumulation of mitochondria in the vicinity of PrPres deposits, and expression of mutant ubiquitin (UBB+1) in neurofibrillary tangles and dystrophic neurites. Prion protein immunoblotting using 3F4 and 1E4 antibodies disclosed multiple bands ranging from approximately 20 kd to 80 kd and lower bands of 15 kd and approximately 10 kd, the latter only seen after a long incubation. These bands were partially resistant to proteinase K pretreatment. This pattern differs from those seen in Creutzfeldt-Jakob disease andresembles those reported in other GSS cases. The approximately 10kd band was recognized with anti-PrP C-terminus antibodies but not with anti-N terminus antibodies, suggesting PrP truncation at the N terminal. This new mutation extends the list of known mutations responsible for GSS disease and reinforces its clinical heterogeneity. Genetic examination of the PRNP gene should be included in the workup of patients with poorly classifiable dementia.

Penetrance in Parkinson's disease related to the LRRK2 R1441G mutation in the Basque country (Spain)†

The LRRK2 R1441G mutation was first identified in Basque families and it is responsible for 46% of familial Parkinsons disease (PD) and for 2.5% of sporadic PD in the PD population of Basque ascent. The aim of this study was to determine LRRK2 R1441G penetrance in PD in the Basque Country (Spain) to help in a more accurate genetic counseling. A total of 59 sibships containing 244 individuals, with a total of 40 PD‐affected relatives, were studied. Genetic testing for the R1441G mutation in the LRRK2 gene was performed in 133 individuals and was positive in 51% of them. Lifetime penetrance of R1441G mutations turned out to be 12.5% at 65 years to 83.4% at 80 years. No gender differences were found in penetrance.

Gene Expression Profiling in Limb-Girdle Muscular Dystrophy 2A

Limb-girdle muscular dystrophy type 2A (LGMD2A) is a recessive genetic disorder caused by mutations in calpain 3 (CAPN3). Calpain 3 plays different roles in muscular cells, but little is known about its functions or in vivo substrates. The aim of this study was to identify the genes showing an altered expression in LGMD2A patients and the possible pathways they are implicated in. Ten muscle samples from LGMD2A patients with in which molecular diagnosis was ascertained were investigated using array technology to analyze gene expression profiling as compared to ten normal muscle samples. Upregulated genes were mostly those related to extracellular matrix (different collagens), cell adhesion (fibronectin), muscle development (myosins and melusin) and signal transduction. It is therefore suggested that different proteins located or participating in the costameric region are implicated in processes regulated by calpain 3 during skeletal muscle development. Genes participating in the ubiquitin proteasome degradation pathway were found to be deregulated in LGMD2A patients, suggesting that regulation of this pathway may be under the control of calpain 3 activity. As frizzled-related protein (FRZB) is upregulated in LGMD2A muscle samples, it could be hypothesized that β-catenin regulation is also altered at the Wnt signaling pathway, leading to an incorrect myogenesis. Conversely, expression of most transcription factor genes was downregulated (MYC, FOS and EGR1). Finally, the upregulation of IL-32 and immunoglobulin genes may induce the eosinophil chemoattraction explaining the inflammatory findings observed in presymptomatic stages. The obtained results try to shed some light on identification of novel therapeutic targets for limb-girdle muscular dystrophies.

Somatic mosaicism in a case of apparently sporadic Creutzfeldt-Jakob disease carrying a de novo D178N mutation in the PRNP gene†‡

Transmissible spongiform encephalopathies (TSEs) are a group of rare fatal neurodegenerative disorders. Creutzfeldt‐Jakob disease (CJD) represents the most common form of TSE and can be classified into sporadic, genetic, iatrogenic and variant forms. Genetic cases are related to prion protein gene mutations but they only account for 10–20% of cases. Here we report an apparently sporadic CJD case with negative family history carrying a mutation at codon 178 of prion protein gene. This mutation is a de novo mutation as the parents of the case do not show it. Furthermore the presence of three different alleles (wild type 129M‐178D and 129V‐178D and mutated 129V‐178N), confirmed by different methods, indicates that this de novo mutation is a post‐zygotic mutation that produces somatic mosaicism. The proportion of mutated cells in peripheral blood cells and in brain tissue was similar and was estimated at approximately 97%, suggesting that the mutation occurred at an early stage of embryogenesis. Neuropathological examination disclosed spongiform change mainly involving the caudate and putamen, and the cerebral cortex, together with proteinase K‐resistant PrP globular deposits in the cerebrum and cerebellum. PrP typing was characterized by a lower band of 21 kDa. This is the first case of mosaicism described in prion diseases and illustrates a potential etiology for apparently sporadic neurodegenerative diseases. In light of this case, genetic counseling for inherited and sporadic forms of transmissible encephalopathies should take into account this possibility for genetic screening procedures.

“Frontotemporoparietal” dementia Clinical phenotype associated with the c.709-1G>A PGRN mutation

Background: Mutations in the progranulin gene (PGRN) are a major cause of frontotemporal lobar degeneration with tau-negative and ubiquitin-positive neuronal inclusions. Most previous studies aimed at characterizing the clinical and neuropsychological phenotype of PGRN mutation carriers included patients with different PGRN mutations, assuming that the common proposed pathogenetic mechanism of haploinsufficiency will lead to a comparable phenotype. Methods: We studied 21 patients with a single pathogenic splicing mutation in the PGRN gene (c.709-1G>A) in the same tertiary referral center using homogenous diagnostic criteria and protocols. All patients were of Basque descent. Results: Patients exhibited a variable phenotype both in age at onset and initial symptoms. Behavioral variant frontotemporal dementia (52.4%) and progressive nonfluent aphasia (23.8%) were the most common presenting syndromes. Apathy was the most common behavioral symptom. Patients developed a relatively rapidly progressive dementia with features that led to a secondary diagnosis in 61.9% of cases 2 years after primary diagnosis. Notably, this secondary or tertiary diagnosis was corticobasal syndrome in 47.6% of cases, which confirmed the neuropsychological features of parietal lobe dysfunction seen at the initial assessment in 81.8% of patients. Conclusions: Patients carrying the c.709-1G>A mutation in the PGRN gene showed heterogeneous clinical and neuropsychological features and commonly developed corticobasal syndrome as the disease progressed.