Brittle bone disease (osteogenesis imperfecta) is an inherited genetic condition that causes bone weakness. It can increase a person’s risk of fractures and other medical complications.
A person with brittle bone disease has weak bones that fracture easily.
It is an inherited condition with several types, ranging from mild to severe. The most severe type results in death during infancy. However, most people who receive proper treatment have a typical life expectancy.
In this article, we take a closer look at the condition, including its types, causes, symptoms, and more.
Brittle bone disease, or osteogenesis imperfecta, is a genetic condition that a person is born with. A person with this condition has bones that fracture easily with even minor impacts.
Globally, brittle bone disease affects 1 in 10,000–20,000 people. Estimates for the United States suggest that 25,000–50,000 people have the condition.
The condition has at least 19 types. The Osteoporosis and Related Bone Diseases National Resource Center details several types of brittle bone disease. The following are the most common:
Type 1
Type 1 is the mildest form of brittle bone disease. Type 1 results in bones that break easily from mild to moderate trauma, mainly before puberty. A person with type 1 brittle bone disease does not have enough collagen.
Type 2
Type 2 is the most severe form of brittle bone disease. It often causes infants to die at birth or shortly afterward because they cannot breathe. Their bones break in the womb.
Infants with type 2 brittle bone disease have severe bone deformities, underdeveloped lungs, and improperly formed collagen.
Type 3
Type 3 is the most severe form of brittle bone disease in people who survive infancy. People with type 3 brittle bone disease are the most likely to experience physical disabilities.
Types 4, 5, and 6
The bones of a person with type 4 brittle bone disease can often break before puberty and sometimes before birth.
They may experience mild to moderate bone deformity and spine and rib cage abnormalities.
The clinical symptoms of types 5 and 6 are similar to those of type 4. Bones have a mesh-like appearance under a microscope in type 5 and a fish scale-like appearance in type 6.
Types 7 and 8
Types 7 and 8 have a similar appearance and symptoms to types 2 and 3.
Researchers are also studying rarer types of brittle bone disease. These forms tend to be moderately severe and similar to types 3 and 4. Some affect the function of bone-forming cells rather than collagen formation.
Most people who have brittle bone disease inherit it from a parent.
People with dominant brittle bone disease make up the majority of cases. They inherit a typical copy of the gene from one parent and a mutated copy from the other parent.
Both parents of people with recessive brittle bone disease have a mutated copy of the gene. However, neither parent has brittle bone disease.
Around 90% of people with brittle bone disease have a mutation in a gene that carries instructions for making type 1 collagen, most commonly COL1A1 but also COL1A2. The body needs type 1 collagen to maintain its structure, particularly for bone tissue, skin, and other connective tissues.
Some mutations prevent the body from producing enough collagen. Others prevent the collagen molecules from developing into their mature form. Some mutations can affect bone-forming cells rather than collagen-forming ones.
All people with brittle bone disease have weak and brittle bones. While some people experience only a few broken bones throughout life, others experience hundreds of bone breaks. Bone breaks may even occur before birth.
Other symptoms vary from person to person and range from mild to severe. They may include:
- deformed or bowed long bones
- small stature
- easy bruising
- loose joints and weak muscles
- blue, purple, or gray sclera (whites of the eyes)
- triangular face
- barrel-shaped rib cage
- curved spine
- collapsed or compressed vertebrae
- brittle, misshapen, or discolored teeth
- hearing impairment
- breathing difficulties
- deformity of the hip joint
When deciding whether a person has brittle bone disease, doctors typically start by asking about their family and medical history.
If a fetus has a parent with brittle bone disease, a doctor can order an ultrasound to check for broken or unusually shaped bones.
Additionally, amniocentesis allows doctors to check whether the fetus has a mutated collagen gene. This procedure involves using a thin needle to extract a small sample of amniotic fluid for testing.
A doctor can also test for brittle bone disease after an infant is born using the following methods:
- X-rays to look for healed fractures or bone breaks
- genetic tests to look for mutations in the collagen gene
- biochemical testing, such as taking a skin sample to test the collagen
Doctors may recommend several types of therapy to treat brittle bone disease.
Exercise and physical therapy can help improve muscle and bone strength and lessen the chances of fracture. Hydrotherapy, which involves movement in water, can help support the bones while a person is exercising.
Some people may also benefit from medications.
For example, bisphosphonates slow the breakdown of existing bone tissue during the formation of new bone. This increases bone mass and strength but does not help the body make typical bone. Adults and children can take bisphosphonates.
Other osteoporosis medications can stop a person from losing bone mass. Denosumab reduces the breakdown of existing bone, while teriparatide increases bone strength. Only adults can take these medications.
Some people with brittle bone disease may need surgery. This can involve inserting rods into the long bones or reducing compression between the top of the spine and the base of the skull.
Additionally, a person with tooth or jaw abnormalities may need dental or orthodontic surgery.
People with the most severe forms of brittle bone disease may die during infancy.
However, most people who receive supportive care and medical management can expect to lead healthy, productive lives with average life span.
A 2016 Danish study published in the
The researchers also noted that brittle bone disease may increase a person’s risk of dying from respiratory and gastrointestinal diseases and trauma.
Doctors usually diagnose moderate or severe brittle bone disease at
A person with brittle bone disease can support their health and reduce their chance of broken bones by:
- eating a nutritious diet and maintaining a moderate weight to prevent additional health problems, such as diabetes and heart disease, and to minimize stress on the bones
- doing as much exercise as possible to strengthen muscles and bones — especially swimming, as the support of water can help prevent bone breaks
- avoiding smoking, drinking alcohol, and consuming caffeine, which can weaken bones
Living with brittle bone disease can affect a person’s mental health. If a person feels depressed, anxious, or worried, they should consider seeking counseling or talking with a healthcare professional.
Mobility aids, such as walkers, canes, crutches, braces, and wheelchairs, can help a person move around safely and prevent fractures.
Infants born with the most severe form of brittle bone disease often face life threatening complications at or shortly after birth.
These can include respiratory problems due to malformed lungs or congestive heart failure. Some people also experience kidney stones.
Brittle bone disease is an inherited condition affecting bone formation.
The primary symptom is weak bones that fracture easily with minimal trauma. Treatments include surgery, osteoporosis medications, and physical therapy.
Most people with brittle bone disease can expect to have an average life span if they receive appropriate medical care and support.