Frontotemporal Dementia: clinical, genetic, and pathological heterogeneity

The current clinical syndrome frontotemporal dementia (FTD) was first described in 1892 by the Czech psychiatrist Arnold Pick. He described a patient with aphasia and behavioural changes with on macroscopic examination marked left frontotemporal atrophy. In 1911, Alois Alzheimer described the detailed microscopic changes, including argyrophilic neuronal inclusions, which are still known as Pick bodies. The term Pick’s disease was introduced in 1926 and was used till the early 90’s to describe the clinical and pathological entity. To date, Pick’s disease is used for a neuropathological subgroup of FTD patients. FTD encompasses distinct canonical syndromes: the behavioural variant of FTD (bvFTD), and two language variants, semantic dementia (SD), and progressive non-fluent aphasia (PNFA). FTD is accompanied by motor neuron disease (MND) in 5 – 15 % of the cases. FTD patients characteristically present at presenile age with variable behavioural changes and language disturbances. The clinical syndrome FTD is part of a wide clinicopathological spectrum designated by the term frontotemporal lobar degeneration (FTLD). The last few years have seen major advances in our understanding of FTD, its genetic causes and pathological substrates. In 1994, a genetic-epidemiological study on FTD was started at the Erasmus University Medical Center of Rotterdam. Since then, over 400 patients have been included in our FTD cohort. The aim of this thesis was to describe and determine the relationship between the clinical presentation, genetics and pathology of FTD, with emphasis on the hereditary form of FTD

Genetic screening in early-onset Alzheimer's disease identified three novel presenilin mutations

Mutations in presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein (APP) are major genetic causes of early-onset Alzheimer's disease (EOAD). Clinical heterogeneity is frequently observed in patients with PSEN1 and PSEN2 mutations. Using whole exome sequencing, we screened a Dutch cohort of 68 patients with EOAD for rare variants in Mendelian Alzheimer's disease, frontotemporal dementia, and prion disease genes. We identified 3 PSEN1 and 2 PSEN2 variants. Three variants, 1 in PSEN1 (p.H21Profs*2) and both PSEN2 (p.A415S and p.M174I), were novel and absent in control exomes. These novel variants can be classified as probable pathogenic, except for PSEN1 (p.H21Profs*2) in which the pathogenicity is uncertain. The initial clinical symptoms between mutation carriers varied from behavioral problems to memory impairment. Our findings extend the mutation spectrum of EOAD and underline the clinical heterogeneity among PSEN1 and PSEN2 mutation carriers. Screening for Alzheimer's disease–causing genes is indicated in presenile dementia with an overlapping clinical diagnosis

Genetic screening in early-onset Alzheimer's disease identified three novel presenilin mutations

Mutations in presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein (APP) are major genetic causes of early-onset Alzheimer's disease (EOAD). Clinical heterogeneity is frequently observed in patients with PSEN1 and PSEN2 mutations. Using whole exome sequencing, we screened a Dutch cohort of 68 patients with EOAD for rare variants in Mendelian Alzheimer's disease, frontotemporal dementia, and prion disease genes. We identified 3 PSEN1 and 2 PSEN2 variants. Three variants, 1 in PSEN1 (p.H21Profs*2) and both PSEN2 (p.A415S and p.M174I), were novel and absent in control exomes. These novel variants can be classified as probable pathogenic, except for PSEN1 (p.H21Profs*2) in which the pathogenicity is uncertain. The initial clinical symptoms between mutation carriers varied from behavioral problems to memory impairment. Our findings extend the mutation spectrum of EOAD and underline the clinical heterogeneity among PSEN1 and PSEN2 mutation carriers. Screening for Alzheimer's disease–causing genes is indicated in presenile dementia with an overlapping clinical diagnosis

Impairments in knowledge of social norms in presymptomatic, prodromal, and symptomatic frontotemporal dementia

INTRODUCTION: We aimed to assess the knowledge of social norms in patients with behavioral variant frontotemporal dementia (bvFTD) with the Dutch version of the Social Norms Questionnaire (SNQ-NL). METHODS: The SNQ-NL was administered in 34 patients with bvFTD, 20 prodromal mutation carriers, 76 presymptomatic mutation carriers, and 56 controls. Group differences and correlations with other neuropsychological tests and gray matter volume were examined. RESULTS: Patients with bvFTD had lower total SNQ-NL scores and more over-adherence errors than presymptomatic mutation carriers and controls (P &lt; 0.001). SNQ-NL performance correlated with tests for executive functioning and social cognition, and with gray matter volume in bilateral frontal and unilateral temporal regions. DISCUSSION: The SNQ-NL can identify impairments in knowledge of social norms in bvFTD, highlighting its significance in clinical diagnosis and upcoming clinical trials. The SNQ-NL currently fails to differentiate presymptomatic mutation carriers from controls; to this end, larger sample sizes from larger cohorts and longitudinal follow-up are warranted. Highlights: The Dutch version of the Social Norms Questionnaire (SNQ-NL) is able to detect impairment in social cognition in symptomatic bvFTD patients. A trend towards a lower performance in prodromal mutation carriers was found. Performance on the SNQ-NL is related to other measures of social cognition, executive functioning, and language. Lower SNQ-NL performance is related to gray matter volume loss in bilateral frontal and temporal regions. The SNQ-NL provides insight into the underlying cause of deficits in social cognition in bvFTD.</p

Occupational differences in a Dutch sample of patients with primary progressive aphasia, behavioral variant frontotemporal dementia, and Alzheimer’s dementia

Background: Cognitive reserve is a potential mechanism to cope with brain damage as a result of dementia, which can be defined by indirect proxies, including education level, leisure time activities, and occupational attainment. In this study we explored the association between dementia diagnosis and type of occupation in a retrospective Dutch outpatient memory clinic sample of patients with primary progressive aphasia (PPA), behavioral variant frontotemporal dementia (bvFTD), and Alzheimer’s Dementia (AD). Methods: We included data from 427 patients (bvFTD n = 87, PPA n = 148, AD n = 192) and compared the frequency of occupations (11 categories) between patients and data from the Dutch census using Pearson Χ2 tests and we calculated odds ratios (OR) by means of multinomial logistic regression analyses. We also investigated patient group differences in age, sex, education, disease duration, and global cognition. Results: The frequency of teachers in patients with PPA was significantly higher than the frequency of teachers in patients with bvFTD [OR = 4.79, p =.007] and AD [OR = 2.04, p =.041]. The frequency of teachers in patients with PPA (16%) was also significantly higher than the frequency of teachers in the Dutch census [5.3%; OR = 3.27, p &lt;.001]. The frequency of teachers in both bvFTD and AD groups were not significantly different from the frequency of teachers in the Dutch census (p =.078 and p =.513, respectively). Conclusions: A potential explanation for our results is the so called “wear and tear” hypothesis, suggesting that teachers have a communication-wise demanding occupation–and therefore are at higher risk to develop PPA. Alternatively, teaching requires continuous communication, hence teachers are more sensitive to subtle changes in their speech and language abilities. Our findings broaden our understanding of the relationship between occupational activity and cognitive reserve in the development of dementia.</p

Longitudinal changes in qualitative aspects of semantic fluency in presymptomatic and prodromal genetic frontotemporal dementia

Background: The semantic fluency test is one of the most widely used neuropsychological tests in dementia diagnosis. Research utilizing the qualitative, psycholinguistic information embedded in its output is currently underexplored in presymptomatic and prodromal genetic FTD. Methods: Presymptomatic MAPT (n = 20) and GRN (n = 43) mutation carriers, and controls (n = 55) underwent up to 6 years of neuropsychological assessment, including the semantic fluency test. Ten mutation carriers became symptomatic (phenoconverters). Total score and five qualitative fluency measures (lexical frequency, age of acquisition, number of clusters, cluster size, number of switches) were calculated. We used multilevel linear regression modeling to investigate longitudinal decline. We assessed the co-correlation of the qualitative measures at each time point with principal component analysis. We explored associations with cognitive decline and grey matter atrophy using partial correlations, and investigated classification abilities using binary logistic regression. Results: The interrater reliability of the qualitative measures was good (ICC = 0.75–0.90). There was strong co-correlation between lexical frequency and age of acquisition, and between clustering and switching. At least 4 years pre-phenoconversion, GRN phenoconverters had fewer but larger clusters (p &lt; 0.001), and fewer switches (p = 0.004), correlating with lower executive function (r = 0.87–0.98). Fewer switches was predictive of phenoconversion, correctly classifying 90.3%. Starting at least 4 years pre-phenoconversion, MAPT phenoconverters demonstrated an increase in lexical frequency (p = 0.009) and a decline in age of acquisition (p = 0.034), correlating with lower semantic processing (r = 0.90). Smaller cluster size was predictive of phenoconversion, correctly classifying 89.3%. Increase in lexical frequency and decline in age of acquisition were associated with grey matter volume loss of predominantly temporal areas, while decline in the number of clusters, cluster size, and switches correlated with grey matter volume loss of predominantly frontal areas. Conclusions: Qualitative aspects of semantic fluency could give insight into the underlying mechanisms as to why the “traditional” total score declines in the different FTD mutations. However, the qualitative measures currently demonstrate more fluctuation than the total score, the measure that seems to most reliably deteriorate with time. Replication in a larger sample of FTD phenoconverters is warranted to identify if qualitative measures could be sensitive cognitive biomarkers to identify and track mutation carriers converting to the symptomatic stage of FTD.</p