Osteopetrosis Symptoms and Treatment

Osteopetrosis is a bone disease that causes bones to be too dense, and this abnormality can lead to easily broken bones. Osteopetrosis causes special bone cells called osteoclasts to function abnormally. Normally, osteoclasts break down old bone tissue as new bone tissue grows. For people with osteopetrosis, the osteoclasts do not break down the old bone tissue. This bone buildup causes bones to overgrow. In the head and spine, this overgrowth puts pressure on nerves and causes neurological problems. In the bones where bone marrow usually forms, the overgrowth can crowd out the bone marrow.

There are multiple types of osteopetrosis, which are described based on the type of genetic inheritance. These include autosomal dominant osteopetrosis, autosomal recessive osteopetrosis, and intermediate autosomal osteopetrosis. Each type can vary in the severity of the condition.

Autosomal Dominant Osteopetrosis (ADO)

Originally called Albers-Schonberg disease after the German radiologist who first described it, this form of osteopetrosis is the mildest type and is usually diagnosed in adults between 20 and 40 years old. Some people may not have any noticeable symptoms. Adults with osteopetrosis who develop symptoms may have frequent bone fractures that don’t heal well. Bone infections (osteomyelitis), pain, degenerative arthritis, and headaches may also occur.

ADO is the most common form of osteopetrosis. Approximately one in 20,000 people have this form of the condition. People with ADO only inherit one copy of the gene, meaning it came from only one parent (known as autosomal dominant inheritance). Those diagnosed with osteopetrosis have a 50% chance of passing the condition on to their children.

Autosomal Recessive Osteopetrosis (ARO)

ARO, also known as malignant infantile osteopetrosis, is the most severe form of osteopetrosis. Infants with ARO have extremely brittle bones (the consistency of which has been compared to sticks of chalk) which break easily. During the birth process, the baby’s shoulder bones may break.

Malignant infantile osteopetrosis is usually apparent at birth. Children with malignant infantile osteopetrosis may develop blood problems such as anemia (low number of red blood cells) and thrombocytopenia (low number of platelets in the blood). Other symptoms include:

• Low levels of calcium (which can cause seizures)
• Pressure on the optic nerve in the brain (leading to visual impairment or blindness)
• Hearing loss
• Facial paralysis
• Frequent bone fractures

This form of osteopetrosis is rare, affecting 1 in 250,000 people. The condition occurs when both parents have an abnormal gene that is passed to the child (called autosomal recessive inheritance). The parents do not have the disorder, even though they carry the gene. Each child they have has a 1 in 4 chance of being born with ARO. Left untreated, the average lifespan for children with ARO is less than ten years.

Intermediate Autosomal Osteopetrosis (IAO)

Intermediate autosomal osteopetrosis is another rare form of osteopetrosis. Only a few cases of the condition have been reported. IAO can be inherited from one or both parents, and typically becomes apparent during childhood. Children with IAO may have an increased risk of bone fracture, as well as anemia. Children with IAO typically do not have the life-threatening bone marrow abnormalities that children with ARO have. However, some children may develop abnormal calcium deposits in their brain, leading to intellectual disabilities. The condition is also linked to renal tubular acidosis, a type of kidney disease.

OL-EDA-ID

In extremely rare cases, osteopetrosis can be inherited through the X chromosome. This is known as OL-EDA-ID, an abbreviation of the symptoms the condition causes—osteopetrosis, lymphedema (abnormal swelling), anhidrotic ectodermal dysplasia (a condition affecting the skin, hair, teeth, and sweat glands), and immunodeficiency. People with OL-EDA-ID are prone to severe, recurrent infections.

Treatment Options

Both the adult and childhood forms of osteopetrosis may benefit from Actimmune injections. Actimmune (interferon gamma-1b) delays the progression of malignant infantile osteopetrosis because it causes an increase in bone resorption (breakdown of old bone tissue) and in red blood cell production.

A bone marrow transplant can provide a cure for select cases of malignant infantile osteopetrosis. Bone marrow transplant has many risks, but the major benefit of improving longer term survival can outweigh the risks in select cases.

Other treatments include nutrition, prednisone (helps improve the blood cell count), and physical and occupational therapy.