MTNR1B and osteoporosis: We found specific osteoporosis-linked SNPs in genes encoding key receptors involved in bone metabolism that are classified into rhodopsin (ADRB2, CNR2, MTNR1B, FSHR, TSHR, LGR4), secretin (CALCR, GIPR), and other T7M (WLS) receptor families (Figure 2A).