To study the molecular mechanisms by which the SP7 variant found in our subject affects osteoblast function, we infected mouse primary chondrocytes and mesenchymal stem cells (MSCs) with retroviruses expressing green fluorescent protein (GFP, as a negative control and an indicator for successful infection), FLAG-tagged human wild-type SP7 or the FLAG-tagged S309W SP7 mutant. This evidence concerns the gene SP7 and infection.