COL1A2 and idiopathic juvenile osteoporosis: Patients with dominant negative mutations in COL1A2 are linked to osteogenesis imperfecta types I–IV, Ehlers-Danlos syndrome type VIIB, recessive Ehlers-Danlos syndrome classical type, idiopathic osteoporosis, and atypical Marfan syndrome (33), whereas haploinsufficiency of COL1A2 leads to milder phenotypes.