TREM2 and Alzheimer disease: Multiple risk genes/loci identified in AD patients encode proteins that are critical for bone homeostasis, such as Apolipoprotein E4 (ApoE4), triggering receptor expressed on myeloid cells 2 (TREM2), Siglec-3(CD33), proline-rich tyrosine kinase 2(PYK2), vacuolar sorting protein 35(VPS35), and sortilin-related receptor 1(SorL1) [85,86,87].