Overview of Osteopetrosis

Osteopetrosis is group of a rare disorders that cause bones to grow abnormally and become overly dense. When bones become overly dense, they are brittle and can fracture (break) easily. In addition, bones may be misshapen and large, causing other problems in the body. For example, changes to the bone size and density of the skull can cause pressure on nerves leading to vision loss, hearing loss, and paralysis of the facial muscles.

As bone increases in size, the amount of space for the bone marrow (soft, sponge-like tissue in the center of most bones that produces blood cells) becomes crowded. Decreases in the amount of space for bone marrow can lead to low levels of cells in the body that fight infection, carry oxygen to the body’s cells, or control bleeding.

Osteopetrosis are genetic diseases that a child inherits from their parents. The disorder may be mild to severe, and symptoms may appear early in infancy or later in adulthood. The treatment options depend on the type of osteopetrosis the person has.  

What happens in osteopetrosis?

Normally, old bone is broken down and new bone is formed. However, this process does not work properly in people with osteopetrosis. Instead, old bone is not broken down as new bone is formed. This causes the bone to develop incorrectly, leading to dense, thick bones that can fracture easily. 

Who Gets Osteopetrosis?

People with a family history of the disease are at greater risk of inheriting it through an abnormal gene that is passed on from one or both parents.

Types of Osteopetrosis

The types of osteopetrosis are broken into categories based on inheritance pattern, age the disease develops, and the severity of the disease. The types include:

  • Autosomal recessive osteopetrosis is the severe infantile form of the disorder. The symptoms of this type develop at or shortly after birth and shorten life expectancy.
  • Autosomal dominant osteopetrosis is the noninfantile form of the disorder and is also known as Albers-Schönberg disease. The symptoms of this type develop later than the infantile form and have a wide range of disease severity. Even within the same family, some people have little or no impact from the disease, while others are severely affected by the disease and have significant disability and shortened life expectancy. People with this type of osteopetrosis may not be diagnosed until adolescence or adulthood.
  • X-linked osteopetrosis is a rare form of the disease and can affect many areas of the body.

Symptoms of Osteopetrosis

The severity of symptoms can vary depending on the type of osteopetrosis. They include:

  • Bone fractures from brittle, dense bones.
  • Nasal congestion from narrowing sinus cavities.
  • Vision and hearing changes from enlarged bones pressing on nerves.
  • Dental problems due to bone changes in the skull and jaw and because teeth come in later than normal.
  • Low blood cell levels due to smaller amounts of bone marrow because of crowding in the center of bones can lead to anemia and infection.
  • Infections in the bone (osteomyelitis).
  • Chronic bone pain.

Cause of Osteopetrosis

Osteopetrosis is a genetic disease that, in most cases, a child inherits from one or both parents. Genes carry information that determines which features are passed to you from your parents. We have two copies of most of our genes, one from each parent.

People with osteopetrosis have a gene that causes the body to make too few or abnormal cells called osteoclasts. When the osteoclasts are missing, old bone is not broken down as new bone is made, leading to dense, weak bones.

The inheritance patterns help determine the type of osteopetrosis the person has.  

  • Autosomal recessive inheritance pattern happens when the parents each carry one copy of the mutated (changed) gene but do not show any signs or symptoms of the disease. It’s important to note that the mutated gene may not be passed from both parents to every child. Some children will not have any copies of the gene, and others may only have one copy, making them a carrier.
  • Autosomal dominant inheritance pattern happens when only one mutated copy of the gene appears. This happens when the child inherits one copy of a mutated gene from one parent; however, sometimes the mutated gene appears with no family history.
  • X-linked inheritance pattern causes a rare form of the disease and happens when a mutation occurs in genes on the X chromosome, one of the two sex chromosomes in each cell. This type of osteopetrosis usually affects boys.