The role of MAPT gene in Chinese dementia patients: a P301L pedigree study and brief literature review

Clinical features and biomarkers of semantic variant primary progressive aphasia with MAPT mutation

BACKGROUND

Semantic variant primary progressive aphasia (svPPA) is generally sporadic, with very few reports of tau pathology caused by MAPT mutations.

METHODS

A 64-year-old man was diagnosed with svPPA with MAPT P301L mutation. Clinical information, cognitive and language functions, multimodal magnetic resonance imaging (MRI), blood biomarkers, fluorodeoxyglucose (FDG) imaging and tau positron emission tomography (PET) were obtained.

RESULTS

Semantic memory impairment was the earliest and most prominent symptom in this family. Tau accumulation and hypometabolism were observed prior to brain atrophy in mutation carriers. Plasma NfL and GFAP concentrations were elevated in the two svPPA patients. Some relative decreases and some relative increases in regional cerebral blood flow (CBF) as measured by arterial spin labelling (ASL) were observed in mutation carriers compared to noncarriers.

CONCLUSIONS

This study describes a large svPPA-affected family with the MAPT P301L mutation and provides an ideal model for inferring underlying pathology and pathophysiological processes in svPPA caused by tauopathies.

Molecular imaging biomarkers in familial frontotemporal lobar degeneration: Progress and prospects

Familial frontotemporal lobar degeneration (FTLD) is a pathologically heterogeneous group of neurodegenerative diseases with diverse genotypes and clinical phenotypes. Three major mutations were reported in patients with familial FTLD, namely, progranulin (GRN), microtubule-associated protein tau (MAPT), and the chromosome 9 open reading frame 72 (C9orf72) repeat expansion, which could cause neurodegenerative pathological changes years before symptom onset. Noninvasive quantitative molecular imaging with PET or single-photon emission CT (SPECT) allows for selective visualization of the molecular targets in vivo to investigate brain metabolism, perfusion, neuroinflammation, and pathophysiological changes. There was increasing evidence that several molecular imaging biomarkers tend to serve as biomarkers to reveal the early brain abnormalities in familial FTLD. Tau-PET with ¹⁸F-flortaucipir and ¹¹C-PBB3 demonstrated the elevated tau position in patients with FTLD and also showed the ability to differentiate patterns among the different subtypes of the mutations in familial FTLD. Furthermore, dopamine transporter imaging with the ¹¹C-DOPA and ¹¹C-CFT in PET and the ¹²³I-FP-CIT in SPECT revealed the loss of dopaminergic neurons in the asymptomatic and symptomatic patients of familial FTLD. In addition, PET imaging with the ¹¹C-MP4A has demonstrated reduced acetylcholinesterase (AChE) activity in patients with FTLD, while PET with the ¹¹C-DAA1106 and ¹¹C-PK11195 revealed an increased level of microglial activation associated with neuroinflammation even before the onset of symptoms in familial FTLD. ¹⁸F-fluorodeoxyglucose (FDG)-PET indicated hypometabolism in FTLD with different mutations preceded the atrophy on MRI. Identifying molecular imaging biomarkers for familial FTLD is important for the in-vivo assessment of underlying pathophysiological changes with disease progression and future disease-modifying therapy. We review the recent progress of molecular imaging in familial FTLD with focused on the possible implication of these techniques and their prospects in specific mutation types.

The Frequency of Genetic Mutations Associated With Behavioral Variant Frontotemporal Dementia in Chinese Han Patients

BACKGROUND

Behavioral variant frontotemporal dementia (bvFTD) is a clinically heterogeneous syndrome with high heredity. However, the frequencies of mutations associated with bvFTD have yet to be determined. The aim of the current study was to investigate the frequency of Chinese Han patients harboring genetic bvFTD variants.

METHODS

A total of 49 bvFTD patients selected from our frontotemporal lobar degeneration database, including 14 familial cases belonging to eight families and 35 sporadic cases were consecutively recruited from July 2014 to December 2019 at Xuanwu Hospital (Beijing, China). Whole-exome sequencing (WES) was performed and repeat-primed PCR was used to test samples for the C9orf72 hexanucleotide repeat expansion mutation. The frequency of genetic variants and the pathogenicity of the novel variants were analyzed.

RESULTS

Ten pathogenic or likely pathogenic variants were identified in 17 bvFTD patients, including C9orf72 repeat expansions, six previously reported mutations and three novel mutations (MAPT p. R5C, p. D54N, GRN p. P451L). Genetic mutations accounted for 27.9% (12/43) of total cases, 87.5% (7/8) of patients with familial bvFTD, and 14.3% (5/35) with sporadic bvFTD. Pathogenic variants mostly occurred in MAPT gene (20.9%, 9/43), followed by C9orf72 repeat expansions (2.3%, 1/43), GRN gene (2.3%, 1/43) and FUS gene (2.3%, 1/43).

CONCLUSION

There was a high prevalence of genetic variants in Chinese bvFTD patients, highlighting the necessity of genetic testing for bvFTD.

Frequency of frontotemporal dementia-related gene variants in Turkey

Just as its clinical heterogeneity, genetic basis of Frontotemporal dementia (FTD) is also diverse and multiple molecular pathways are thought to be involved in disease pathogenesis. In the present study, FTD- related genes were evaluated in a Turkish cohort of 175 index FTD patients with a gene panel including GRN, MAPT, TARDBP, FUS, CHMP2B and VCP genes. Potential genetic associations were prospected in 16 patients (9.1%); five variants (p.(Gly35Glufs) and p.(Cys253Ter) in GRN; p.(Arg95Cys) in VCP; p.(Met405Val) in TARDBP and p.(Pro636Leu) in MAPT) were classified as pathogenic (P) or likely pathogenic (LP), in four familial and one sporadic patients. Three novel variants in MAPT, CHMP2B and FUS were also identified in familial cases. The most common pathogenic variants were observed in the GRN gene with a frequency of 1.14% (2/175) and this rate was 4.57% (8/175), including variants of uncertain significance (VUS). In this study with the largest cohort of Turkish FTD patients, GRN and MAPT variants were identified as the most common genetic associations; and rare causes like VCP, TARDBP, CHMP2B and FUS variants are recommended to be considered in patients with compatible clinical findings.

Tau PET Imaging with [18F]PM-PBB3 in Frontotemporal Dementia with MAPT Mutation

BACKGROUND

Flortaucipir (AV-1451) and pyridinyl-butadienyl-benzothiazole 3 (PBB3) are newly developed and commonly used positron emission tomography (PET) tracers to detect tau deposition in tauopathies, including frontotemporal dementia (FTD). [18F]PM-PBB3, as a second-generation compound, has not been described in FTD so far.

OBJECTIVE

We aim to explore the in vivo performance of [18F]PM-PBB3 tau PET in an FTD case caused by microtubule-associated protein tau (MAPT) mutation and compare the binding to different tau strains between AV-1451 and PBB3.

METHODS

We reported the clinical and FDG, [18F]AV45 amyloid and [18F]PM-PBB3 tau PET findings in a patient with FTD of P301L MAPT mutation. Based on our results and published data, we summarized and compared the different utilities of tau PET tracers of AV-1451 and PBB3 in FTD with MAPT mutation.

RESULTS

The patient demonstrated slightly diffuse [18F]PM-PBB3 tau deposition in cerebral lobes especially in the left frontal lobe overlapping with the hypometabolic region detected by FDG PET. From our analysis of 35 FTD patients with MAPT mutation who underwent tau PET, AV-1451 was positive in all (n = 11) patients with mutations known to cause three and four repeat (3R/4R) tau deposition and in 14.3% (n = 2/14) of 4R tauopathies, while positive PBB3 retention was found in all patients with both 3R/4R (n = 2) and 4R (n = 8) tau.

CONCLUSIONS

[18F]PM-PBB3 tau PET assisted the diagnosis of FTD with P301L MAPT mutation, and might be useful in the in vivo detection of both 3R/4R and 4R tau domains in the brain of FTD with MAPT mutation.

Early anterior cingulate involvement is seen in presymptomatic MAPT P301L mutation carriers

Background

PET imaging of glucose metabolism has revealed presymptomatic abnormalities in genetic FTD but has not been explored in MAPT P301L mutation carriers. This study aimed to explore the patterns of presymptomatic hypometabolism and atrophy in MAPT P301L mutation carriers.

Methods

Eighteen asymptomatic members from five families with a P301L MAPT mutation were recruited to the study, six mutation carriers, and twelve mutation-negative controls. All participants underwent standard behavioural and cognitive assessment as well as [¹⁸F]FDG-PET and 3D T1-weighted MRI brain scans. Regional standardised uptake value ratios (SUVR) for the PET scan and volumes calculated from an automated segmentation for the MRI were obtained and compared between the mutation carrier and control groups.

Results

The mean (standard deviation) estimated years from symptom onset was 12.5 (3.6) in the mutation carrier group with a range of 7 to 18 years. No differences in cognition were seen between the groups, and all mutation carriers had a global CDR plus NACC FTLD of 0. Significant reduction in [¹⁸F] FDG uptake in the anterior cingulate was seen in mutation carriers (mean 1.25 [standard deviation 0.07]) compared to controls (1.36 [0.09]). A similar significant reduction was also seen in grey matter volume in the anterior cingulate in mutation carriers (0.60% [0.06%]) compared to controls (0.68% [0.08%]). No other group differences were seen in other regions.

Conclusions

Anterior cingulate hypometabolism and atrophy are both apparent presymptomatically in a cohort of P301L MAPT mutation carriers. Such a specific marker may prove to be helpful in stratification of presymptomatic mutation carriers in future trials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00777-9.

Genetics of frontotemporal dementia in China

Backgbround: Frontotemporal dementia (FTD) is the second most common presenile dementia, characterized by prominent behavioral, language, and cognitive impairment, which has a strong genetic component contributing to its pathogenesis. Due to geographical and ethnic variability, the prevalence of the causative genes of FTD may be different. Methods: To explore the genetics of FTD in the Chinese population, we reviewed 97 closely related studies that were searched in PubMed and Web of Science. In this review, we summarized the characteristics of each FTD gene. We also reassessed their pathogenicity and revised some mutations from pathogenic to uncertain significance according to the American College of Medical Genetics and Genomics (ACMG). Results: Thirty-two rare variants in genes of MAPT, GRN, C9orf72, CHCHD10, VCP, and TBK1 were identified in Chinese FTD populations, including 25 pathogenic mutations and seven variants of uncertain significance (VUS). Among them, the frequency of rare variants in the CHCHD10 gene was the highest. Surprisingly, twelve variants reported as pathogenic mutations were revised as VUS by ACMG. The correlations between genes and clinical manifestations were MAPT and frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), GRN and frontotemporal lobar degeneration with TDP-43 proteinopathy (FTLD-TDP), C9orf72/CHCHD10/TBK1 and amyotrophic lateral sclerosis (ALS)-FTD spectrum, and VCP corresponds inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia (IBMPFD). Conclusions: It is necessary to strictly interpret the contributions of genes to diseases by ACMG. MAPT is the most common pathogenic gene for FTD in China.

Phenotype Heterogeneity and Genotype Correlation of MAPT Mutations in a Chinese PUMCH Cohort

Frontotemporal dementia (FTD) is a heterogeneous disease both clinically and pathologically. Genetic mutation in microtubule-associated protein tau (MAPT) is the most common cause of FTD, and the phenotype is related to the mutation location. However, the phenotype and genotype correlation varies somewhat among different cohorts and ethnicities. Whole-genome next-generation sequencing (NGS) was carried out for 1351 patients with dementia at Peking Union Medical College Hospital. MAPT variations classified as pathogenic and of uncertain significance were identified. Demographic information, clinical presentations, and neuroimaging were collected, and the phenotype-genotype correlation was analyzed with a concurrent literature review. Twenty-four patients were enrolled; 8 patients carrying the D177V mutation are discussed separately. The average onset age was young, and most of them had a positive family history. Cognitive dysfunction, behavior, and personality changes as well as aphasia were the most common presentations. Most structural MRIs showed asymmetrical atrophy of the temporal lobe, with/without similar changes in the frontal lobe. L266V carriers presented with youngest onset typical behavior variant FTD or aphasia; P301L carriers presented with behavior variant FTD or aphasia. Functional MRI and molecular imaging also showed that the involved areas were similar to those with structural atrophy. D296N carriers presented atypical parkinsonism and cognitive dysfunction at older ages. Eight D177V carriers had extraordinarily different manifestations. The clinical phenotype of most of them was not FTD, though cerebral vascular lesions were obvious in some of them. MAPT mutation is rare in Chinese dementia patients. The phenotype and genotype correlation is specific and overlaps. The D177V mutation is possibly not directly pathogenic in our cohort. Some of the variants might increase the genetic risk of neurodegenerative diseases.