COL1A1 and osteogenesis imperfecta: Since COL1 expression was decreased in Insig1/2 cKO mice, the abnormalities may resemble osteogenesis imperfecta, which is a congenital bone disorder characterized by thinner and fragile bones that affects 6–7 in 100 000 individuals worldwide.24 Altogether, our results indicate that either too much or too little cholesterol causes calvarial bone abnormalities through dysregulation of Col1a1 expression.