TREM2 and behavioral variant of frontotemporal dementia: Homozygous pathogenic variants in TREM2 (Triggering Receptor Expressed On Myeloid Cells 2) and TYROBP (TYRO protein tyrosine kinase-binding protein) can cause a syndrome characterized by bone pain, cysts, and fractures that begin to appear in the third decade of life, and a frontal syndrome (similar to bvFTD) that typically occurs in the fourth decade.