Antonella Alberici

Mutation within TARDBP leads to Frontotemporal Dementia without motor neuron disease

It has been recently demonstrated that the 43‐kDa transactive response (TAR)‐DNA‐binding protein (TARDBP) is the neuropathological hallmark of Frontotemporal Dementia (FTD) with ubiquitin‐positive and tau‐negative inclusions. Large series of FTD patients without motor neuron disease have been previously analysed, but no TARDBP mutation was identified. The aim of the present study was to evaluate whether TARDBP gene mutations may be associated with FTD. We report that a pathogenetic TARDBP mutation is causative of behavioural variant FTD (bvFTD). An aged woman in her seventies initially started to present apathy and depression associated with impairment in executive functions. The diagnosis of bvFTD (apathetic syndrome) was accomplished by three‐year follow‐up, and structural and functional neuroimaging. By five‐years after onset, extensive electrophysiological investigations excluded subclinical motor neuron disease. In this patient, a single base substitution c.800A>G of TARDBP gene was identified. This mutation, already described as causative of ALS, predicted the amino acidic change arginine to serine at position 267 (N267S). In silico analysis demonstrated that this substitution generates a new phosphorylation site, and western blot analysis on lymphoblastoid cells reported a decrease of protein expression in N267S mutation carrier. Our study suggests that TARDBP mutations can be pathogenetic of bvFTD without motor neuron disease. TARDBP screening needs to be considered in FTD cases.

High Prevalence of Pathogenic Mutations in Patients with Early-Onset Dementia Detected by Sequence Analyses of Four Different Genes

Clinical differential diagnosis of early-onset dementia (EOD) includes familial Alzheimer disease (FAD) and hereditary prion disease. In both disease entities, postmortem brain histopathological examination is essential for unambiguous diagnosis. Mutations in the genes encoding the presenilins (PS1 and PS2) and amyloid precursor protein (APP) are associated with FAD, whereas mutations in the prion protein (PrP) gene are associated with prion disease. To investigate the proportion of EOD attributable to known genes, we prospectively (i.e., antemortem) screened these four genes for mutations by sequencing genomic PCR products from patients with EOD before age 60 years. Family history for dementia was positive (PFH) in 16 patients, negative (NFH) in 17 patients, and unknown (UFH) in 3 patients. In 12 patients, we found five novel mutations (in PS1, F105L; in PS2, T122P and M239I; and in PrP, Q160X and T188K) and five previously reported mutations (in APP, in three patients who were most likely unrelated, V717I; in PS1, A79V and M139V; and in PrP, P102L and T183A) that are all considered to be disease causing. Of these 12 patients, 9 had PFH. This indicates a detection rate of 56% (9/16) in patients with PFH. We found two mutations (APP V717I) in two of the three UFH patients, and only one mutation (PrP T188K) in 1 of the 17 patients with NFH. We conclude that because of the lack of specific antemortem diagnostic markers for FAD and hereditary prion disease, all four genes should be included in a molecular diagnostic program in patients with EOD who had PFH.

Diffusion tensor imaging and voxel based morphometry study in early progressive supranuclear palsy

Background: A comprehensive characterisation of grey and white matter changes in progressive supranuclear palsy (PSP), the second most common extrapyramidal syndrome after Parkinson disease, is still not available. Objective: To evaluate grey and white matter changes in mild PSP patients by voxel based morphometry (VBM) and diffusion tensor imaging (DTI), respectively. Methods: 14 mild PSP patients and 14 healthy controls entered the study and underwent a clinical and neuropsychological evaluation according with a standardised assessment. Each subject had a structural magnetic resonance imaging (MRI) study. Processing analysis of MRI data was carried out according to optimised VBM and fractional anisotropy was determined. Results: Compared with the controls, in PSP patients VBM analysis showed a significant clusters of reduced grey matter in premotor cortex, frontal operculum, anterior insula, hippocampus, and parahippocampal gyrus, bilaterally. With regard to subcortical brain regions, the pulvinar, dorsomedial and anterior nuclei of the thalamus, and superior and inferior culliculum were affected bilaterally. A bilateral decrease in fractional anisotropy in superior longitudinal fasciculus, anterior part of corpus callosum, arcuate fascicolus, posterior thalamic radiations, and internal capsule, probably involving the cortico-bulbar tracts, was present in PSP patients. Conclusions: These data provide evidence for both grey and white matter degeneration in PSP from the early disease stage. These structural changes suggest that atrophy of cortical and subcortical structures and neurodegeneration of specific fibre tracts contribute to neurological deficits in PSP.

IDENTIFICATION AND CHARACTERIZATION OF A KAPPA B/REL BINDING SITE IN THE REGULATORY REGION OF THE AMYLOID PRECURSOR PROTEIN GENE

Several observations support the hypothesis that pathogenetic mechanisms of β amyloid formation in Alzheimers disease may involve alterations in amyloid precursor protein (APP) gene expression. In this regard, molecular dissection of the APP gene transcriptional regulation is of primary importance. We report evidence that members of the family of transcription factors NFκB/Rel can specifically recognize two identical sequences located in the 5′-regulatory region of APP. These sequences, which we refer to as APPκB sites, interact preferentially with p50-containing members of the family. In particular, p50 homodimers and p50/p65 and p50/c-Rel heterodimers act as transcriptional activators at the APPκB site. Finally, the nuclear complex specifically binding to the APPκB sites proves to be an integral part of neurons and lymphocytes.

Presenilin 1 Protein Directly Interacts with Bcl-2

Presenilin proteins are involved in familial Alzheimers disease, a neurodegenerative disorder characterized by massive death of neurons. We describe a direct interaction between presenilin 1 (PS1) and Bcl-2, a key factor in the regulation of apoptosis, by yeast two-hybrid interaction system, by co-immunoprecipitation, and by cross-linking experiments. Our data show that PS1 and Bcl-2 assemble into a macromolecular complex, and that they are released from this complex in response to an apoptotic stimulus induced by staurosporine. The results support the idea of cross-talk between these two proteins during apoptosis.

Tau forms in CSF as a reliable biomarker for progressive supranuclear palsy

Objective: In CSF, extended (55 kDa) and truncated (33 kDa) tau forms have been previously recognized, and the tau 33 kDa/55 kDa ratio has been found significantly reduced in progressive supranuclear palsy (PSP) vs in other neurodegenerative disorders. The aim of this study was to evaluate the diagnostic value of the CSF tau form ratio as a biomarker of PSP and to correlate the structural anatomic changes as measured by means of voxel-based morphometry (VBM) to CSF tau form ratio decrease. Methods: A total of 166 subjects were included in the study (21 PSP, 20 corticobasal degeneration syndrome, 44 frontotemporal dementia, 29 Alzheimer disease, 10 Parkinson disease, 15 dementia with Lewy bodies, and 27 individuals without any neurodegenerative disorder). Each patient underwent a standardized clinical and neuropsychological evaluation. In CSF, a semiquantitative immunoprecipitation was developed to evaluate CSF tau 33 kDa/55 kDa ratio. MRI assessment and VBM analysis was carried out. Results: Tau form ratio was significantly reduced in patients with PSP (0.504 ± 0.284) when compared to age-matched controls (0.989 ± 0.343), and to patients with other neurodegenerative conditions (range = 0.899–1.215). The area under the curve (AUC) of the receiver operating characteristic analysis in PSP vs other subgroups ranged from 0.863 to 0.937 (PSP vs others, AUC = 0.897, p < 0.0001). VBM study showed that CSF tau form ratio decrease correlated significantly with brainstem atrophy. Conclusions: Truncated tau production, which selectively affects brainstem neuron susceptibility, can be considered a specific and reliable marker for PSP. Tau form ratio was the lowest in progressive supranuclear palsy with no overlap with any other neurodegenerative illness. GLOSSARY: AD = Alzheimer disease; AUC = area under the curve; BADL = Basic Activity of Daily Living; CBDS = corticobasal degeneration; CON = controls; DLB = dementia with Lewy bodies; DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, 4th edition; FTD = frontotemporal dementia; IADL = Instrumental Activities of Daily Living; MMSE = Mini-Mental State Examination; MSA = multiple system atrophy; PD = Parkinson disease; PSP = progressive supranuclear palsy; ROC = receiver operating characteristic; UPDRS = Unified Parkinson’s Disease Rating Scale; VBM = voxel-based morphometry.

Association of late-onset Alzheimer disease with a genotype of PLAU, the gene encoding urokinase-type plasminogen activator on chromosome 10q22.2

Urokinase-type plasminogen activator (uPA) converts plasminogen to plasmin. Plasmin is involved in processing of amyloid precursor protein and degrades secreted and aggregated amyloid-β, a hallmark of Alzheimer disease (AD). PLAU, the gene encoding uPA, maps to chromosome 10q22.2 between two regions showing linkage to late-onset AD (LOAD). We genotyped a frequent C/T single nucleotide polymorphism in codon 141 of PLAU (P141L) in 347 patients with LOAD and 291 control subjects. LOAD was associated with homozygous C/C PLAU genotype in the whole sample (χ2=15.7, P=0.00039, df 2), as well as in all sub-samples stratified by gender or APOE ε4 carrier status (χ2≥ 6.84, P≤0.033, df 2). Odds ratio for LOAD due to homozygosity C/C was 1.89 (95% confidence interval 1.37–2.61). PLAU is a promising new candidate gene for LOAD, with allele C (P141) being a recessive risk allele or allele T (L141) conferring protection.

Granulin mutation drives brain damage and reorganization from preclinical to symptomatic FTLD

Granulin (GRN) mutations have been identified as a major cause of frontotemporal lobar degeneration (FTLD) by haploinsufficiency mechanism, although their effects on brain tissue dysfunction and damage still remain to be clarified. In this study, we investigated the pattern of neuroimaging abnormalities in FTLD patients, carriers and noncarriers of GRN Thr272fs mutation, and in presymptomatic carriers. We assessed regional gray matter (GM) atrophy, and resting (RS)-functional magnetic resonance imaging (fMRI). The functional connectivity maps of the salience (SN) and the default mode (DMN) networks were considered. Frontotemporal gray matter atrophy was found in all FTLD patients (more remarkably in those GRN Thr272fs carriers), but not in presymptomatic carriers. Functional connectivity within the SN was reduced in all FTLD patients (again more remarkably in those mutation carriers), while it was enhanced in the DMN. Conversely, presymptomatic carriers showed increased connectivity in the SN, with no changes in the DMN. Our findings suggest that compensatory mechanisms of brain plasticity are present in GRN-related FTLD, but with different patterns at a preclinical and symptomatic disease stage.

Brain Magnetic Resonance Imaging Structural Changes in a Pedigree of Asymptomatic Progranulin Mutation Carriers

Mutations in the progranulin (PGRN) gene have been recently demonstrated as a cause of frontotemporal lobar degeneration (FTLD) with ubiquitin-immunoreactive neuronal inclusion (FTD-U). Neuropathologic, clinical, and neuroimaging features associated with PGRN mutations have been carefully described. No studies on asymptomatic subjects carrying pathogenetic PGRN mutations are available yet. These would be crucial for establishing the timing of brain changes and bringing new insight into disease pathogenesis and disease course. The aim of this study was to evaluate structural brain morphology using diffusion tensor imaging (DTI) and voxel-based morphometry (VBM) in asymptomatic carriers of PGRN delCACT mutation belonging to a four-generation FTLD pedigree (mean age, 37.0 +/- 12.0). The evaluation of the family proband presenting with progressive nonfluent aphasia at 53 years of age, revealed left frontotemporal hypoperfusion and atrophy. VBM analysis of gray and white matter reductions revealed no differences between asymptomatic carriers (n = 7) and controls (n = 15), and between no-carriers (n = 10) and controls (p < 0.001). DTI analysis revealed a reduction in fractional anisotropy in healthy PGRN mutation carriers in the left uncinate fasciculus, connecting the orbito-frontal regions to the temporal pole, and in the left inferior occipitofrontal fasciculus, connecting the parieto-occipital cortex to the dorsolateral frontal cortex (p < 0.001). No significant difference in fractional anisotropy between no-carriers and controls was found. Our data indicate loss of white matter integrity as an early preclinical feature in familial FTD that might antedate the onset of specific neurologic features. Alteration of fiber tracts within the perisylvian language network might represent the early hallmark of subsequent aphasia onset. The study of other pedigrees of asymptomatic PGRN mutation carriers is warranted.

Alzheimer disease-associated cystatin C variant undergoes impaired secretion

CST3 is the coding gene for cystatin C (CysC). CST3 B/B homozygosity is associated with an increased risk of developing Alzheimer disease. We performed CysC analysis on human primary skin fibroblasts obtained from donors carrying A/A, A/B, and B/B CST3. Pulse-chase experiments demonstrated that the release of the B variant of CysC has a different temporal pattern compared to that of the A one. Fibroblasts B/B homozygous displayed a reduced secretion of CysC due to a less efficient cleavage of the signal peptide, as suggested by high-resolution Western blot analysis and by in vitro assay. In the brain, the reduced level of CysC may represent the molecular factor responsible for the increased risk of Alzheimer disease.