Begoña Indakoetxea

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.

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.

Identification of a novel THAP1 mutation at R29 amino-acid residue in sporadic patients with early-onset dystonia.

Dystonia is a movement disorder characterized by involuntary, sustained muscular contractions affecting one or more sites of the body and abnormal postures. The clinical spectrum of dystonia is diverse: however, the most common form of the disease is primary torsion dystonia (PTD). PTD usually onsets in infancy or adolescence and affects the trunk, neck, or limbs. Two genes are associated with PTD, DYT1 (OMIM 128100; TOR1A) and DYT6 (OMIM 609520; THAP1). Mutations in THAP1 were, first, identified in families presenting with cranial or cervical dystonia that frequently progressed to involve other body regions, and later, in families presenting with early-onset generalized dystonia with prominent spasmodic dysphonia. Here, 24 patients presenting with either generalized (6) or cervical dystonia (18) were investigated for the presence of THAP1 mutations. The mean age at onset was 48 years (range 9–77 years). All patients provided written informed consent to participate in this study. Sequencing analysis of the coding region of the THAP1 gene revealed the presence of a novel c.86G>A transition resulting in p.Arg29Gln in two sporadic cases suffering from early-onset cervical dystonia and early-onset generalized dystonia, respectively. This novel mutation, located in exon 2 of the THAP1 gene, affects an amino-acid previously identified as mutated in families presenting with multifocal and generalized dystonia. Furthermore, R29 amino acid is conserved between species; suggesting, p.Arg29Gln is likely to be pathogenic. Although both p.Arg29Gln mutation carriers are from the same geographical region, there is no evidence of a common founder. A novel silent, mutation which resulted in c.81T>C transition causing p.Leu27Leu was also identified in a sporadic, late-onset dystonia patient presenting with involuntary movements in the neck at the age of sixty; however, its pathogenic role remains unclear. Both novel THAP1 mutations were absent in a Spanish series of 182 control chromosomes. We concluded that pathogenic mutations were only found in early-onset cases. THAP1 mutations occur throughout the entire gene; however, many seem to cluster in the THAP domain of the protein, including the novel THAP1 mutations described here (Fig. 1). It has been suggested that mutations in the THAP domain may reduce the DNA binding ability of THAP; therefore we speculate that mutations at R29 may also act via this mechanism. Clinical features of both patients carrying p.Arg29Gln mutation are described below. This case is a 55 years old man who, at the age of 9, presented with a right-sided torticollis which persisted for more than a year. A surgical intervention was given around his neck and in the right upper limb. Since then, no improvement was determined however the disease showed slow progression. At 54, he noted having cognitive changes and difficulties in speech and ingestion. There was no family history of movement disorders and his mother died with cognitive decline of late onset. Dystonia was mainly present in the face and proximal left upper limb. Left sided torticollis was found with a tendency of retrocollis and fluctuating involvement of both platysma. The trapezia and ECMs were hypertrophic. MRI brain was normal. The cervical spine showed mild disc protrusion at C5-C6 and C6-C7 without radicular involvements. To control the dystonia, increased dose of Botulinum toxin (Dysport), up to 700 units, was required. This case is a 33 years old man who, at the age of 14, presented with abnormal pain sensation in the left upper limb. He progressed to develop dystonic movements in the hand which usually presented as wrist flexion on the radial side and, occasionally, on the ulnar side. In addition, the left upper limb showed forced abduction. Dystonia has now spread to the left foot. His grandmother was diagnosed as having Parkinson’s disease and his great-aunt with possible blepharospasm. Brain MRI was normal and cervical spine showed minimal disc protrusion at C5-C6 without any compression noted. The arm abduction was controlled with botulinum toxin; however, dystonia remained uncontrolled and no additional medication was given. Serum copper, ceruloplasmin, calcium, phosphate, ferritin, and glucose were normal in both cases. To summarize, THAP1 mutations may be present in sporadic, early-onset, cervical, and generalized dystonia.

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.

Investigation of the role of rare TREM2 variants in frontotemporal dementia subtypes

Frontotemporal dementia (FTD) is a clinically and genetically heterogeneous disorder. Rare TREM2 variants have been recently identified in families affected by FTD-like phenotype. However, genetic studies of the role of rare TREM2 variants in FTD have generated conflicting results possibly because of difficulties on diagnostic accuracy. The aim of the present study was to investigate associations between rare TREM2 variants and specific FTD subtypes (FTD-S). The entire coding sequence of TREM2 was sequenced in FTD-S patients of Spanish (n = 539) and German (n = 63) origin. Genetic association was calculated using Fisher exact test. The minor allele frequency for controls was derived from in-house genotyping data and publicly available databases. Seven previously reported rare coding variants (p.A28V, p.W44X, p.R47H, p.R62H, p.T66M, p.T96K, and p.L211P) and 1 novel missense variant (p.A105T) were identified. The p.R47H variant was found in 4 patients with FTD-S. Two of these patients showed cerebrospinal fluid pattern of amyloid beta, tau, and phosphorylated-tau suggesting underlying Alzheimers disease (AD) pathology. No association was found between p.R47H and FTD-S. A genetic association was found between p.T96K and FTD-S (p = 0.013, odds ratio = 4.23, 95% Confidence Interval [1.17-14.77]). All 6 p.T96K patients also carried the TREM2 variant p.L211P, suggesting linkage disequilibrium. The remaining TREM2 variants were found in 1 patient, respectively, and were absent in controls. The present findings provide evidence that p.T96K is associated with FTD-S and that p.L211P may contribute to its pathogenic effect. The data also suggest that p.R47H is associated with an FTD phenotype that is characterized by the presence of underlying AD pathology.

“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.

MAPT H1 Haplotype is Associated with Late-Onset Alzheimer’s Disease Risk in APOEɛ4 Noncarriers: Results from the Dementia Genetics Spanish Consortium

The MAPT H1 haplotype has been linked to several disorders, but its relationship with Alzheimers disease (AD) remains controversial. A rare variant in MAPT (p.A152T) has been linked with frontotemporal dementia (FTD) and AD. We genotyped H1/H2 and p.A152T MAPT in 11,572 subjects from Spain (4,327 AD, 563 FTD, 648 Parkinsons disease (PD), 84 progressive supranuclear palsy (PSP), and 5,950 healthy controls). Additionally, we included 101 individuals from 21 families with genetic FTD. MAPT p.A152T was borderline significantly associated with FTD [odds ratio (OR) = 2.03; p = 0.063], but not with AD. MAPT H1 haplotype was associated with AD risk (OR = 1.12; p = 0.0005). Stratification analysis showed that this association was mainly driven by APOE ɛ4 noncarriers (OR = 1.14; p = 0.0025). MAPT H1 was also associated with risk for PD (OR = 1.30; p = 0.0003) and PSP (OR = 3.18; p = 8.59 × 10-8) but not FTD. Our results suggest that the MAPT H1 haplotype increases the risk of PD, PSP, and non-APOE ɛ4 AD.

A Common Haplotype Associated with the Basque 2362AG-TCATCT Mutation in the Muscular Calpain-3 Gene

Limb-girdle muscular dystrophy type 2A (LGMD2A) is caused by any of over 150 mutations in the calpain-3 (CAPN3) gene. Of those, 2362AG → TCATCT is particularly prevalent in Basque patients, and this mutation was hypothesized to have arisen in the Basque Country. To explore the natural history of this mutation, we genotyped 65 Basque and non-Basque patients with LGMD2A who carry the 2362AG → TCATCT mutation for four microsatellites within or flanking the gene. A particular haplotype was found in three-fourths of the patients and was assumed to be ancestral. From the average number of recombinations and mutations accumulated from this ancestral haplotype, the age of the 2362AG → TCATCT mutation was estimated to be 50 generations (i.e., 1,250 years), which is more recent than the Paleolithic Basque heritage. The subsequent spread of the 2362AG → TCATCT mutation can be related to gene flow out of the Basque Country, even across a cultural border.

Prion protein codon 129 polymorphism modifies age at onset of frontotemporal dementia with the C.709-1G>A progranulin mutation.

Frontotemporal lobar degeneration because of mutations in the progranulin (PGRN) gene presents a high variability both in the clinical phenotype and age of onset of disease. Factors that influence this variability remain largely unknown. The aim of our study was to determine whether selected genetic variables modify age at onset of disease in our series of 21 patients with a single splicing mutation (c.709-1G>A) in the PGRN gene, all of whom were of Basque descent. In our analysis, we included the following genetic variables: PGRN rs5848 and rs9897526 polymorphisms, APOE and microtubule-associated protein tau genotypes, and PRNP codon 129 polymorphism. We found no association between PGRN polymorphisms, APOE and microtubule-associated protein tau genotypes, and age at onset of the disease; whereas we report evidence for an association between PRNP codon 129 polymorphism and age at onset of disease in frontotemporal dementia-PGRN(+) patients. MM homozygous carriers presented onset of disease on average 8.5 years earlier than patients who carried at least 1 valine on their PRNP codon 129 (MV or VV). The biological justification for this association remains speculative.

Neuropsychological Features of Asymptomatic c.709-1G>A Progranulin Mutation Carriers

Mutations in the progranulin (PGRN) gene have been identified as a cause of frontotemporal dementia (FTD). However, little is known about the neuropsychological abilities of asymptomatic carriers of these mutations. The aim of the study was to assess cognitive functioning in asymptomatic c.709-1G>A PGRN mutation carriers. We hypothesized that poorer neuropsychological performance could be present before the development of clinically significant FTD symptoms. Thirty-two asymptomatic first-degree relatives of FTD patients carrying the c.709-1G>A mutation served as study participants, including 13 PGRN mutation carriers (A-PGRN+) and 19 non-carriers (PGRN-). A neuropsychological battery was administered. We found that the A-PGRN+ participants obtained significantly poorer scores than PGRN- individuals on tests of attention (Trail-Making Test Part A), mental flexibility (Trail-Making Test Part B), and language (Boston Naming Test). Poorer performance on these tests in asymptomatic PGRN mutation carriers may reflect a prodromal phase preceding the onset of clinically significant symptoms of FTD.