CLINICAL EXOME SEQUENCING IN DEMENTIAS: A PRELIMINARY STUDY

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.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.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.Our preliminary results imply significant diagnostic yield in identifying rare genetic causes of dementia, combining comprehensive clinical exome sequencing and targeted C9orf72 expansion testing.