CTSK and bone disorder: The genes that have been implicated in AFF include genes associated with monogenic bone disorders, often without use of antiresorptive drugs, such as, COL1A1, COL1A2, ALPL, PHEX, CTSK, LRP5, SERPINF1, IFITM5, CRTAP, PLS3, and OFD1, and genes involved in the action of BPs, such as GGPS1 and ATRAID. Although studies have been conducted with genetic analysis in AFF families and genome-wide or exon-wide association analysis in unrelated cases, none of the results from the studies has been fully confirmed, mostly because of limitations in sample size.