COL1A1 and osteoporosis: Indeed, proline residues along the helical regions of both chains required hydroxylation by prolyl4‐hydroxylase 1, and the subsequent substitution of Pro could modify the structure of the collagen chains and induce lower bone resistance.23, 24, 25 Finally, the very rare p.Arg708Gln variant in COL1A2 was associated with a severe osteoporosis phenotype previously reported in an older patient.19 A striking finding is that these patients were COL1A2 carriers with variable severity in bone phenotype, but none carried COL1A1 variants.