OI, or “brittle bone disease,” is a condition causing fragile bones that break easily, sometimes for no obvious reason. Some people with OI have only a few fractures in their lifetimes. Others have hundreds.1 People who have severe forms of OI have fragile bones that are also deformed. Most people with OI experience physical disability. OI also can cause weak muscles, brittle teeth, a curved spine, and hearing loss. Most forms of OI are caused by abnormal genes that are passed down from one or both parents to their children.
There are currently 11 types of OI. Types I through IV are the most common. They are autosomal dominant forms of the disease. Autosomal dominance is a pattern of inheritance common to some genetic diseases. “Autosomal” means that the abnormal gene is located on one of the numbered, or non-sex, chromosomes. “Dominant” means that a single copy of the abnormal gene is enough to cause the disease; in other words, a person only needs to get the abnormal gene from one parent in order to inherit the disease, even though the matching gene from the other parent is normal. This is in contrast to an autosomal recessive disorder, where two copies of the mutation are needed to cause the disease; in other words, a person must inherit the abnormal gene from both parents in order to inherit the disease. Types VI through XI are autosomal recessive. 2,3,4
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