Most types of OI are inherited in an autosomal dominant pattern. Almost all infants with the severe type II OI are born into families without a family history of the condition. Usually, the cause in these families is a new mutation in the egg or sperm or very early embryo in the COL1A1 or COL1A2 gene. In the milder forms of OI, 25-30 percent of cases occur as a result of new mutations. The other cases are inherited from a parent who has the condition. Whether a person has OI due to a new mutation or an inherited genetic change, an adult with the disorder can pass the condition down to future generations.
In autosomal dominant inherited OI, a parent who has OI has one copy of a gene mutation that causes OI. With each of his/her pregnancies, there is a 1 in 2 (50 percent) chance to pass on the OI gene mutation to a child who would have OI, and a 1 in 2 (50 percent) chance to pass on the normal version of the gene to a child who would not have OI.
Rarely, OI can be inherited in an autosomal recessive pattern. Most often, the parents of a child with an autosomal recessive disorder are not affected but are carriers of one copy of the altered gene. Autosomal recessive inheritance means two copies of the gene must be altered for a person to be affected by the disorder. The autosomal recessive form of type III OI usually results from mutations in genes other than COL1A1 and COL1A2.