rs1800012

rs1800012 is a G-to-T substitution in the first intron of COL1A1, located within a binding site for the transcription factor Sp1, rather than a coding change. The T allele binds Sp1 with higher affinity, increasing COL1A1 relative to COL1A2 transcription and skewing the ratio of type I collagen alpha chains, which reduces collagen fibril stability. This altered collagen structure is associated with lower bone mineral density and higher fracture, disc-degeneration, and tendon/ligament injury risk, and in this dataset it is paired with COL5A1 rs12722 for connective-tissue context.