ARL4D and osteoporosis: Taken together, this study (1) identified and characterized BMD genes, including 141 class 2 genes that lacked prior association with bone biology, (2) prioritized the class 2 genes based on magnitude of BMD change, human relevance, or pleiotropy, (3) offered clues on pathways, such as vesicle transport, governing bone cell biology in BMD pathologies, and (4) underscored the potential role of the genes, such as Arl4d, Ncald, and Rab3ip, in low BMD pathologies, including osteoporosis.