Parkinsonian syndrome in familial frontotemporal dementia

Parkinsonism, movement disorders and genetics in frontotemporal dementia

Frontotemporal dementia (FTD) refers to a group of clinically and genetically heterogeneous neurodegenerative disorders that are a common cause of adult-onset behavioural and cognitive impairment. FTD often presents in combination with various hyperkinetic or hypokinetic movement disorders, and evidence suggests that various genetic mutations underlie these different presentations. Here, we review the known syndromatic-genetic correlations in FTD. Although no direct genotype-phenotype correlations have been identified, mutations in multiple genes have been associated with various presentations. Mutations in the genes that encode microtubule-associated protein tau (MAPT) and progranulin (PGRN) can manifest as symmetrical parkinsonism, including the phenotypes of Richardson syndrome and corticobasal syndrome (CBS). Expansions in the C9orf72 gene are most frequently associated with familial FTD, typically combined with motor neuron disease, but other manifestations, such as symmetrical parkinsonism, CBS and multiple system atrophy-like presentations, have been described in patients with these mutations. Less common gene mutations, such as those in TARDBP, CHMP2B, VCP, FUS and TREM2, can also present as atypical parkinsonism. The most common hyperkinetic movement disorders in FTD are motor and vocal stereotypies, which have been observed in up to 78% of patients with autopsy-proven FTD. Other hyperkinetic movements, such as chorea, orofacial dyskinesias, myoclonus and dystonia, are also observed in some patients with FTD.

Sex hormone-related neurosteroids differentially rescue bioenergetic deficits induced by amyloid-β or hyperphosphorylated tau protein

Alzheimer's disease (AD) is an age-related neurodegenerative disease marked by a progressive cognitive decline. Metabolic impairments are common hallmarks of AD, and amyloid-β (Aβ) peptide and hyperphosphorylated tau protein--the two foremost histopathological signs of AD--have been implicated in mitochondrial dysfunction. Neurosteroids have recently shown promise in alleviating cognitive and neuronal sequelae of AD. The present study evaluates the impact of neurosteroids belonging to the sex hormone family (progesterone, estradiol, estrone, testosterone, 3α-androstanediol) on mitochondrial dysfunction in cellular models of AD: human neuroblastoma cells (SH-SY5Y) stably transfected with constructs encoding (1) the human amyloid precursor protein (APP) resulting in overexpression of APP and Aβ, (2) wild-type tau (wtTau), and (3) mutant tau (P301L), that induces abnormal tau hyperphosphorylation. We show that while APP and P301L cells both display a drop in ATP levels, they present distinct mitochondrial impairments with regard to their bioenergetic profiles. The P301L cells presented a decreased maximal respiration and spare respiratory capacity, while APP cells exhibited, in addition, a decrease in basal respiration, ATP turnover, and glycolytic reserve. All neurosteroids showed beneficial effects on ATP production and mitochondrial membrane potential in APP/Aβ overexpressing cells while only progesterone and estradiol increased ATP levels in mutant tau cells. Of note, testosterone was more efficient in alleviating Aβ-induced mitochondrial deficits, while progesterone and estrogen were the most effective neurosteroids in our model of AD-related tauopathy. Our findings lend further support to the neuroprotective effects of neurosteroids in AD and may open new avenues for the development of gender-specific therapeutic approaches in AD.

Phenotypic variability related to C9orf72 mutation in a large Sardinian kindred

We investigated intrafamilial phenotypic variability in carriers of the C9orf72 mutation, analysing clinical, neuropsychological and imaging characteristics of various members from a large Sardinian kindred with FTD or ALS. We compared these with those of C9 + patients in our ALS and FTD cohorts. Results showed that three patients carried the C9orf72 mutation: two with ALS and one with FTD and Parkinsonism. C9 + patients in our bvFTD Sardinian cohort had a higher frequency of Parkinsonism than non-mutated patients (75% vs. 36.3%, p <0.02). Parkinsonism was present in 2.7% of our ALS cohort and 3.3% of the C9 + patients. The prevalence of Parkinsonism in C9 + patients in the bvFTD and ALS cohorts showed a statistically significant difference (p <0.006). In conclusion, Parkinsonism was frequently associated with FTD but not ALS in a large Sardinian family, a finding reflected in the wider C9orf72 associated Sardinian ALS and FTD populations.

Frontotemporal dementia-associated N279K tau mutant disrupts subcellular vesicle trafficking and induces cellular stress in iPSC-derived neural stem cells

Background

Pallido-ponto-nigral degeneration (PPND), a major subtype of frontotemporal dementia with parkinsonism related to chromosome 17 (FTDP-17), is a progressive and terminal neurodegenerative disease caused by c.837 T > G mutation in the MAPT gene encoding microtubule-associated protein tau (rs63750756; N279K). This MAPT mutation induces alternative splicing of exon 10, resulting in a modification of microtubule-binding region of tau. Although mutations in the MAPT gene have been linked to multiple tauopathies including Alzheimer’s disease, frontotemporal dementia and progressive supranuclear palsy, knowledge regarding how tau N279K mutation causes PPND/FTDP-17 is limited.

Results

We investigated the underlying disease mechanism associated with the N279K tau mutation using PPND/FTDP-17 patient-derived induced pluripotent stem cells (iPSCs) and autopsy brains. In iPSC-derived neural stem cells (NSCs), the N279K tau mutation induced an increased ratio of 4-repeat to 3-repeat tau and accumulation of stress granules indicating elevated cellular stress. More significant, NSCs derived from patients with the N279K tau mutation displayed impaired endocytic trafficking as evidenced by accumulation of endosomes and exosomes, and a reduction of lysosomes. Since there were no significant differences in cellular stress and distribution of subcellular organelles between control and N279K skin fibroblasts, N279K-related vesicle trafficking defects are likely specific to the neuronal lineage. Consistently, the levels of intracellular/luminal vesicle and exosome marker flotillin-1 were significantly increased in frontal and temporal cortices of PPND/FTDP-17 patients with the N279K tau mutation, events that were not seen in the occipital cortex which is the most spared cortical region in the patients.

Conclusion

Together, our results demonstrate that alterations of intracellular vesicle trafficking in NSCs/neurons likely contribute to neurodegeneration as an important disease mechanism underlying the N279K tau mutation in PPND/FTDP-17.

Genetic Identification Is Critical for the Diagnosis of Parkinsonism: A Chinese Pedigree with Early Onset of Parkinsonism

BACKGROUND

A number of hereditary neurological diseases display indistinguishable features at the early disease stage. Parkinsonian symptoms can be found in numerous diseases, making it difficult to get a definitive early diagnosis of primary causes for patients with onset of parkinsonism. The accurate and early diagnosis of the causes of parkinsonian patients is important for effective treatments of these patients.

METHODS

We have identified a Chinese family (82 family members over four generations with 21 affected individuals) that manifested the characterized symptoms of parkinsonism and was initially diagnosed as Parkinson's disease. We followed up with the family for two years, during which we carried out clinical observations, Positron Emission Tomography-Computed Tomography neuroimaging analysis, and exome sequencing to correctly diagnose the case.

RESULTS

During the two-year follow-up period, we performed comprehensive medical history collection, physical examination, and structural and functional neuroimaging studies of this Chinese family. We found that the patient exhibited progressive deteriorated parkinsonism with Parkinson disease-like neuropathology and also had a good response to the initial levodopa treatment. However, exome sequencing identified a missense mutation, N279K, in exon 10 of MAPT gene, verifying that the early parkinsonian symptoms in this family are caused by the genetic mutation for hereditary frontotemporal lobar dementia.

CONCLUSIONS

For the inherited parkinsonian patients who even show the neuropathology similar to that in Parkinson's disease and have initial response to levodopa treatment, genetic identification of the molecular basis for the disease is still required for defining the early diagnosis and correct treatment.

De novo FUS mutations are the most frequent genetic cause in early-onset German ALS patients

In amyotrophic lateral sclerosis (ALS) patients with known genetic cause, mutations in chromosome 9 open reading frame 72 (C9orf72) and superoxide dismutase 1 (SOD1) account for most familial and late-onset sporadic cases, whereas mutations in fused in sarcoma (FUS) can be identified in just around 5% of familial and 1% of overall sporadic cases. There are only few reports on de novo FUS mutations in juvenile ALS patients. To date, no systematic evaluation on the frequency of de novo FUS mutations in early-onset ALS patients has been conducted. Here, we screened a cohort of 14 early-onset sporadic ALS patients (onset age <35 years) to determine the frequency of mutations in C9orf72, SOD1, and FUS in this defined patient cohort. All patients were recruited prospectively by a single center in a period of 38 months. No mutations were detected in SOD1 or C9orf72; however, we identified 6 individuals (43%) carrying a heterozygous FUS mutation including 1 mutation that has not been described earlier (c.1504delG [p.Asp502Thrfs*27]). Genetic testing of parents was possible in 5 families and revealed that the mutations in these patients arose de novo. Three of the 6 identified patients presented with initial bulbar symptoms. Our study identifies FUS mutations as the most frequent genetic cause in early-onset ALS. Genetic testing of FUS thus seems indicated in sporadic early-onset ALS patients especially if showing predominant bulbar symptoms and an aggressive disease course.