Molecular Genetics of Frontotemporal Dementia

Abstract

Abstract Frontotemporal dementia (FTD) is a nonAlzheimer's form of dementia. Onset age lies in the mid‐to‐late 50s. FTD affects the frontal and/or the temporal lobes and is clinically divided into two main categories: behavioural variant (bvFTD) and language variant. FTD is characterised by heterogeneous pathology defined by pathogenic protein inclusions: microtubule‐associated protein tau (MAPT), ubiquitin/transactive responses (TAR) deoxyribonucleic acid (DNA) ‐binding protein 43 (TDP)‐43, fused in sarcoma (FUS) and p62. MAPT , progranulin ( PGRN ) and, recently, C9orf72 genes represent the three main genetic markers associated with FTD. In addition, genetic variability in TDP‐43 , charged multivesicular body protein 2B ( CHMP2B ), valosin‐containing protein ( VCP ), FUS and TMEM106B genes contribute to ⩽5% of cases. Research tools such as genome‐wide association studies and exome and genome sequencing hold promise to further uncover the genetic underpinnings of this complex disorder. Key Concepts: Frontotemporal dementia (FTD) is a nonAlzheimer's form of dementia; it affects behaviour, cognition and language, while memory (in the early phases). The anatomical areas of the brain that are affected by atrophy are the frontal and the temporal lobes; based on this fact FTD is considered part of the spectrum called frontotemporal lobar degeneration (FTLD). FTD is a complex disease with insidious onset; no therapeutic measures are available as yet. Behavioural variant FTD (bvFTD) is the most common syndrome of FTD, which is associated with gradual deterioration of behaviour and cognition. Different protein inclusions in the brain are used to classify the pathology associated with FTLD. TDP‐43 and tau pathology represent the most common (∼90%) types of pathological signatures associated with FTLD. MAPT , PGRN and C9orf72 are the major (∼95%) genetic markers associated with familial FTD. TMEM106B regulates granulin protein levels. Genome‐wide association studies (GWASs) and next‐generation sequencing technologies whole exome sequencing (WES) and whole genome sequencing (WGS) hold promise for dissecting the genetic aetiology of complex diseases; in molecular genetics these technologies help in screening a wide range of genetic variabilities from SNPs to CNVs in large cohorts across different populations.