Type VII: Generalized
Overview of Osteogenesis Imperfecta (OI):
Osteogenesis imperfecta (OI) is a genetic disorder, which is sometimes referred to as “brittle bone disease.” The name, osteogenesis imperfecta, means imperfect bone formation. OI is named after its primary clinical feature, which involves bones that fractures easily. The fragile bones can fracture with everyday movements such as opening a door or carrying a backpack.
Genetics:
In most cases, OI is inherited in an autosomal dominant pattern. The remaining cases have an autosomal recessive inheritance. OI is caused by mutations in genes that encode for type I collagen or proteins involved in production of type I collagen. Therefore, affected patients have decreased production of type I collagen or dysfunctional type I collagen. Collagen is the framework for which bones are formed around. Type I collagen is a structural protein in connective tissue throughout the body, that is necessary to have strong bones. This defective collagen makes the bones fragile. Collagen is found in bone, tendon, ligament, skin, and sclerae. This explains many of the features of this condition.
Time to Play the Brain Game:
Q) There is a cure for Osteogenesis Imperfecta. True or False?
A) False. Symptoms can be managed by caring for broken bones, pain medications, therapy and surgery.
Clinical Features of OI:
There are many types of OI with varying degrees of severity, so not all patients have all of the following features:
- Fractures of bones, which can lead to deformities of the affected bone
- Short stature (often from fractures within the vertebrae preventing appropriate growth)
- Scoliosis (also from vertebral fractures)
- Neurologic signs and symptoms (from vertebral fractures that lead to nerve root compression)
- Blue sclerae ( sclerae can also be tinted purple or gray)
- Hearing loss (from fractures in the ossicles, which are small bones in the middle ear that aid in sound transmission from the outer ear to the inner ear)
- Teeth that quickly wear down (brittle teeth)
- Loose joints and skin
- Easy bruising ( fragile skin)
- Barrel shaped rib cage
Time to Play the Brain Game:
Q) If the whites of the patients eyes have a blue tint this is indicative of OI. True or False?
A) True. Blue sclera which is a blue or purplish tint in the white portion of the eyes that indicates OI. The blue tint is caused by thin or transparent scleral collagen found within the eye.
Types of OI:
There are at least 9 different types of OI. An extensive review of the types is outside the scope of this article. More detail can be found at https://www.omim.org/ which is a website designed for professionals concerned with genetic disorders. Here, we briefly discuss the more common types of OI:
- Type I: This is the least severe form of OI. Fractures occur at variable rates, and therefore deformity is uncommon. Affected patients usually have a normal height. Typically, patients start developing fractures as toddlers, when they are starting to walk. The rate of fractures typically begins to decline after puberty. However, patients may present with premature or accelerated osteoporosis in adulthood. Hearing loss may also occur. Blue or purple tinted sclera is a common feature for type I. Type I is the most common form of OI seen.
- Type II: This type is referred to as the lethal perinatal form. Affected patients often develop numerous fractures while in utero. These patients usually die in utero or early infancy. They typically die from severe fractures or pulmonary complications.
- Type III and above: Even though these are separate types of OI, the signs and symptoms often overlap, so an expert in OI is usually needed to accurately determine which type a patient has. These forms range in severity from moderate to severe. Affected patients can have any combination of the features listed above with varying degrees of severity.
**please note that not all OI cases have tinted sclerae **
Time to Play the Brain Game:
Q) Most people with OI lead productive and successful lives. True or False?
A) True
Diagnosis:
OI can be diagnosed easily if a patient presents with bone fragility and a positive family history or several non-bone-related manifestations. However, it is not always easy to make the diagnosis. Sometimes, a collagen biopsy or genetic DNA testing is required to confirm the diagnosis.
Different Methods of testing for OI include:
- X-rays to show osteopenia
- DNA sequencing of the collagen from a blood sample
- Biochemical testing of the collagen from a skin biopsy
- DXA scan
When faced with patients with unexplained fractures, it is important to also think about other, more common diagnoses, such as physical abuse, rickets (in children), osteoporosis, or other conditions that cause decreased bone strength.