The cause is genetic mosaicism; that is, some of, or most of, the germ cells of one parent have a dominant form of OI, but not enough of their somatic cells do to cause symptoms or obvious disability in the parent—the parents different cells have two (or more) sets of slightly different DNA. : 1513  It has been clinically observed that ≈5–10% of cases of OI types II and III are attributable to genetic mosaicism. : 532

Pathophysiology
People with OI are either born with defective connective tissue, born without the ability to make it in sufficient quantities, or, in the rarest genetic types, born with deficiencies in other aspects of bone formation such as chaperone proteins, the Wnt signaling pathway, the BRIL protein, et cetera. In type I the collagens structure itself is normal, it is just its quantity that is low. : 1516  Types II, III and IV are usually, but not always, related to a deficiency of type I collagen. One possible deficiency arises from an amino acid substitution of glycine to a bulkier amino acid, such as alanine, in the collagen proteins triple helix structure. The larger amino acid side-chains lead to steric effects that creates a bulge in the collagen complex, which in turn influences both the molecular nanomechanics and the interaction between molecules, which are both compromised. Depending on both the location of the substitution and the amino acid being used instead, different effects are seen which account for the type diversity in OI despite the same two collagen genes being responsible for most cases.
: 247  If affected, it is up to the family to consider whether or not they want to terminate the pregnancy and try again—raising questions of medical ethics and a womans right to choose.Without intervention, patients with the most common mutations causing osteogenesis imperfecta have a 50% chance per gestation of passing on the disorder, as these mutations are inherited in an autosomal dominant pattern of Mendelian inheritance. : 247  Those with the rare autosomal recessive forms of OI have a 25% chance of passing on the disorder. Genetic testing of the affected members of the family can be used to determine which inheritance pattern applies. : 101 As OI type I may be difficult to detect in a newborn child, the cord blood of the child can be tested to determine if it has been passed on if the family has already rejected the more invasive genetic screening methods. : 247  In more severe cases, the diagnosis may be able to be done via ultrasound, especially if OI is already a possibility. : 248  An ethical concern with prenatal screening for OI often arises when parents inquire as to how severely affected their child will be—such questions are as yet difficult to answer conclusively. : 382 If a non-affected person has already had a child with OI, there is a greater likelihood (although still quite remote), that their future children will have OI due to genetic mosaicism.