Background: Dementias are clinically and genetically heterogeneous group of neurodegenerative disorders. Often, dementias with genetic etiology are clinically indistinguishable from non-genetic ones. The aim of this retrospective study was to evaluate the yield of clinical exome sequencing in dementias, potentially associated with monogenic genetic predisposition.
Subjects and methods: For this purpose 20 consecutive patients younger than 65 years were studied in the period from January 2014 to December 2017; 14 with the diagnosis of Frontotemporal dementia (FTD), 3 with early-onset Alzheimer disease (EOAD) and 3 with unspecified dementia. In addition to clinical exome sequencing including 57 genes associated with dementia, C9orf72 hexanucleotide expansion as tested in all patients.
Results: We found genetic etiology in 6 patients: 2 mutations in the PSEN1 gene (p.Pro264Ser and p.Phe105Cys) in the EOAD patients, C9orf72 expansion and MAPT (c.1920+16C>T), mutation in the FTD group of patients as well as MAPT (c.1920+16C>T) mutation and likely pathogenic mutation in the TYROBP mutation (p.Asp32Asn) in patients with unspecified diagnosis.
Conclusions: Our preliminary results imply significant diagnostic yield in identifying rare genetic causes of dementia, combining comprehensive clinical exome sequencing and targeted C9orf72 expansion testing.