Behavioral variant of frontotemporal dementia in carriers of biallelic TREM2 variants: cases study.

Introduction: First reports associated mutations in triggering receptors expressed on myeloid cells 2 (TREM2) with autosomal recessive Nasu-Hakola disease characterized by painful bone cysts and progressive presenile dementia with psychotic symptoms; however, recent TREM2 biallelic rare variants are suggested to be causative also for the behavioral variant of frontotemporal dementia (bvFTD) without bone involvement.

Material and methods: Clinical data of three unrelated bvFTD patients carrying TREM2 biallelic variants were evaluated. All patients underwent neurological, psychiatric, and cognitive evaluation and neuroimaging. A full neuropsychological assessment was performed in two cases.

Results: Two patients carried compound heterozygous TREM2 variants, p.R62C and p.T66M, and one carried the homozygous p.D87N variant. Based on all obtained clinical and neuroimaging data, a behavioral variant of frontotemporal dementia was diagnosed in all cases. Their clinical manifestation was typical with neuropsychiatric and cognitive features, without bone abnormalities.

Conclusions: Despite all three subjects partially resembling clinical manifestations of Nasu-Hakola disease with TREM2 mutations, we reveal some distinct features, including age of onset, neuroimaging findings, or disease course.