Individuals homozygous for loss of function mutations in TREM2 [24] invariably develop polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy (PLOSL), also known as Nasu-Hakola disease (NHD), which manifests as early-onset presenile dementia with frequent bone cysts [25], or as frontotemporal dementia (FTD) [26] with seizures and corpus callosum atrophy. Here, TREM2 is linked to frontotemporal dementia.