Parastoo Momeni

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 Alzheimers 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.

Progranulin mutations and amyotrophic lateral sclerosis or amyotrophic lateral sclerosis–frontotemporal dementia phenotypes

Objective: Mutations in the progranulin (PGRN) gene were recently described as the cause of ubiquitin positive frontotemporal dementia (FTD). Clinical and pathological overlap between amyotrophic lateral sclerosis (ALS) and FTD prompted us to screen PGRN in patients with ALS and ALS–FTD. Methods: The PGRN gene was sequenced in 272 cases of sporadic ALS, 40 cases of familial ALS and in 49 patients with ALS–FTD. Results: Missense changes were identified in an ALS–FTD patient (p.S120Y) and in a single case of limb onset sporadic ALS (p.T182M), although the pathogenicity of these variants remains unclear. Conclusion:PGRN mutations are not a common cause of ALS phenotypes.

Analysis of IFT74 as a candidate gene for chromosome 9p-linked ALS-FTD

BackgroundA new locus for amyotrophic lateral sclerosis – frontotemporal dementia (ALS-FTD) has recently been ascribed to chromosome 9p.MethodsWe identified chromosome 9p segregating haplotypes within two families with ALS-FTD (F476 and F2) and undertook mutational screening of candidate genes within this locus.ResultsCandidate gene sequencing at this locus revealed the presence of a disease segregating stop mutation (Q342X) in the intraflagellar transport 74 (IFT74) gene in family 476 (F476), but no mutation was detected within IFT74 in family 2 (F2). While neither family was sufficiently informative to definitively implicate or exclude IFT74 mutations as a cause of chromosome 9-linked ALS-FTD, the nature of the mutation observed within F476 (predicted to truncate the protein by 258 amino acids) led us to sequence the open reading frame of this gene in a large number of ALS and FTD cases (n = 420). An additional sequence variant (G58D) was found in a case of sporadic semantic dementia. I55L sequence variants were found in three other unrelated affected individuals, but this was also found in a single individual among 800 Human Diversity Gene Panel samples.ConclusionConfirmation of the pathogenicity of IFT74 sequence variants will require screening of other chromosome 9p-linked families.

FTD and ALS: a tale of two diseases

The first reports of disorders that in terms of cognitive and behavioral symptoms resemble frontotemporal dementia (FTD) and in terms of motor symptoms resemble amyotrophic lateral sclerosis (ALS) bring us back to the second half of the 1800s. Over the last 150 years, and especially in the last two decades, there has been growing evidence that FTD signs can be seen in patients primarily diagnosed with ALS, implying clinical overlap among these two disorders. In the last decade pathological investigations and genetic screening have contributed tremendously in elucidating the pathology and genetic variability associated with FTD and ALS. To the most important recentdiscoveries belong TAR DNA binding protein [TARDBP or TDP-43] and the fused in sarcoma gene [FUS] and their implication in these disorders.FTD and ALS are the focus of this review which aims to 1. summarize clinical features by describing the diagnostic criteria and specific symptomatology, 2. describe the morphological aspects and related pathology, 3. describe the genetic factors associated with the diseases and 4. summarize the current status of clinical trials and treatment options. A better understanding of the clinical, pathological and genetic features characterizing FTD and ALS will shed light into overlaps among these two disorders and the underpinning mechanisms that contribute to the onset and development. Nevertheless, advancements in the knowledge of the biology of these two disorders will help developing novel and, hopefully, more effective diagnostic and treatment options.

Characteristics of frontotemporal dementia patients with a Progranulin mutation.

Mutations in the Progranulin gene (PGRN) recently have been discovered to be associated with frontotemporal dementia (FTD) linked to 17q21 without identified MAPT mutations. The range of mutations of PGRN that can result in the FTD phenotype and the clinical presentation of patients with PGRN mutations have yet to be determined.

Heterogeneity within a large kindred with frontotemporal dementia: a novel progranulin mutation.

Background: Frontotemporal dementia (FTD) in several 17q21-linked families was recently explained by truncating mutations in the progranulin gene (GRN). Objective: To determine the frequency of GRN mutations in a cohort of Caucasian patients with FTD without mutations in known FTD genes. Methods: GRN was sequenced in a series of 78 independent FTD patients including 23 familial subjects. A different Calabrian dataset (109 normal control subjects and 96 FTD patients) was used to establish the frequency of the GRN mutation. Results: A novel truncating GRN mutation (c.1145insA) was detected in a proband of an extended consanguineous Calabrian kindred. Segregation analysis of 70 family members revealed 19 heterozygous mutation carriers including 9 patients affected by FTD. The absence of homozygous carriers in a highly consanguineous kindred may indicate that the loss of both GRN alleles might lead to embryonic lethality. An extremely variable age at onset in the mutation carriers (more than five decades apart) is not explained by APOE genotypes or the H1/H2 MAPT haplotypes. Intriguingly, the mutation was excluded in four FTD patients belonging to branches with an autosomal dominant mode of inheritance of FTD, suggesting that another novel FTD gene accounts for the disease in the phenocopies. It is difficult to clinically distinguish phenocopies from GRN mutation carriers, except that language in mutation carriers was more severely compromised. Conclusion: The current results imply further genetic heterogeneity of frontotemporal dementia, as we detected only one GRN-linked family (about 1%). The value of discovering large kindred includes the possibility of a longitudinal study of GRN mutation carriers.

FUS and TDP43 genetic variability in FTD and CBS.

This study aimed to evaluate genetic variability in the FUS and TDP-43 genes, known to be mainly associated with amyotrophic lateral sclerosis (ALS), in patients with the diagnoses of frontotemporal lobar degeneration (FTLD) and corticobasal syndrome (CBS). We screened the DNA of 228 patients for all the exons and flanking introns of FUS and TDP-43 genes. We identified 2 novel heterozygous missense mutations in FUS: P106L (g.22508384C>T) in a patient with behavioral variant frontotemporal dementia (bvFTD) and Q179H in several members of a family with behavioral variant FTD. We also identified the N267S mutation in TDP-43 in a CBS patient, previously only reported in 1 ALS family and 1 FTD patient. Additionally, we identified 2 previously reported heterozygous insertion and deletion mutations in Exon 5 of FUS; Gly174-Gly175 del GG (g. 4180-4185 delGAGGTG) in an FTD patient and Gly175-Gly176 ins GG (g. 4185-4186 insGAGGTG) in a patient with diagnosis of CBS. Not least, we have found a series of variants in FUS also in neurologically normal controls. In summary, we report that genetic variability in FUS and TDP-43 encompasses a wide range of phenotypes (including ALS, FTD, and CBS) and that there is substantial genetic variability in FUS gene in neurologically normal controls.

Screening for C9ORF72 repeat expansion in FTLD

In the present study we aimed to determine the prevalence of C9ORF72 GGGGCC hexanucleotide expansion in our cohort of 53 frontotemporal lobar degeneration (FTLD) patients and 174 neurologically normal controls. We identified the hexanucleotide repeat, in the pathogenic range, in 4 (2 bv-frontotemporal dementia (FTD) and 2 FTD-amyotrophic lateral sclerosis [ALS]) out of 53 patients and 1 neurologically normal control. Interestingly, 2 of the C9ORF72 expansion carriers also carried 2 novel missense mutations in GRN (Y294C) and in PSEN-2(I146V). Further, 1 of the C9ORF72 expansion carriers, for whom pathology was available, showed amyloid plaques and tangles in addition to TAR (trans-activation response) DNA-binding protein (TDP)-43 pathology. In summary, our findings suggest that the hexanucleotide expansion is probably associated with ALS, FTD, or FTD-ALS and occasional comorbid conditions such as Alzheimers disease. These findings are novel and need to be cautiously interpreted and most importantly replicated in larger numbers of samples.

Implication of common and disease specific variants in CLU, CR1, and PICALM

Two recent genome-wide association studies (GWAS) for late onset Alzheimers disease (LOAD) revealed 3 new genes: clusterin (CLU), phosphatidylinositol binding clathrin assembly protein (PICALM), and complement receptor 1 (CR1). In order to evaluate association with these genome-wide association study-identified genes and to isolate the variants contributing to the pathogenesis of LOAD, we genotyped the top single nucleotide polymorphisms (SNPs), rs11136000 (CLU), rs3818361 (CR1), and rs3851179 (PICALM), and sequenced the entire coding regions of these genes in our cohort of 342 LOAD patients and 277 control subjects. We confirmed the association of rs3851179 (PICALM) (p = 7.4 × 10(-3)) with the disease status. Through sequencing we identified 18 variants in CLU, 3 of which were found exclusively in patients; 8 variants (out of 65) in CR1 gene were only found in patients and the 16 variants identified in PICALM gene were present in both patients and controls. In silico analysis of the variants in PICALM did not predict any damaging effect on the protein. The haplotype analysis of the variants in each gene predicted a common haplotype when the 3 single nucleotide polymorphisms rs11136000 (CLU), rs3818361 (CR1), and rs3851179 (PICALM), respectively, were included. For each gene the haplotype structure and size differed between patients and controls. In conclusion, we confirmed association of CLU, CR1, and PICALM genes with the disease status in our cohort through identification of a number of disease-specific variants among patients through the sequencing of the coding region of these genes.

Clinical and pathological features of an Alzheimer's disease patient with the MAPT ΔK280 mutation

We identified a case of Alzheimers disease with a deletion of the lysine residue at codon 280 (Delta K280) in exon 10-encoded microtubule-binding repeat domain of the tau gene (MAPT). This mutation was originally identified in a sporadic case of frontotemporal dementia (FTD) with a family history of Parkinsons disease. In the original report, the authors were careful in their assessment of the pathogenicity and suggested one could not be sure whether the mutation was pathogenic or not. The mutation has always presented a conundrum because it is the only known mutation, of assumed pathogenicity, which increases the proportion of 3-repeat tau mRNA in in vitro assays. Here we present the clinical and pathological features of a new case with this mutation and discuss whether the mutation is indeed pathogenic