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Severe malignant osteopetrosis (SMO) is a form of osteopetrosis that is sometimes called marble bone disease or malignant infantile osteopetrosis (MIOP). Severe malignant osteopetrosis is a very severe form of osteopetrosis. While exact numbers are not known, it is thought that about 1 in 250,000 children are born with SMO.
What happens in the body with SMO?
In normal bone development, bone material is replaced by new bone over and over again. Cells called osteoblasts help create new bone material. Other cells called osteoclasts remove the old bone material.
In people with osteopetrosis, the osteoclasts do not function the right way. As a result, abnormal bone development happens. This can cause many problems in the body, such as:
- Blood disorders
- Difficulty fighting infections
- Bone fractures
- Problems with vision and hearing
- Abnormal look of the face and head
Common characteristics of SMO
In SMO, the buildup of bone materials can narrow the space inside the bone. This means there is less space to make bone marrow. Bone marrow is where new blood cells are formed. Less space to make bone marrow can cause:
- Anemia due to low red blood cells. Symptoms of anemia include pale skin and lack of energy
- Bleeding problems because of low platelets. Platelets are blood cells the body needs to help stop bleeding
- Repeated infections because of low white blood cells. White blood cells are needed to fight infections
With SMO, there can also be a narrowing of the tunnels within the bones of the skull. The nerves for vision and hearing pass through these tunnels. These nerves can be squeezed by bones that overdevelop because of SMO. This causes patients to have problems with their vision and hearing.
Patients often suffer serious effects from SMO. These may include:
- Failure to thrive and slow growth in childhood
- Difficulty seeing or blindness
- Hearing loss
- Abnormal head shape
- Bone marrow failure, causing anemia
- Infections that happen often and over and over
- Repeated bone fractures
SMO can also cause a lower life expectancy. Most children with SMO who are untreated pass away within the first 10 years of life.