What is Autosomal Recessive Osteopetrosis Type 1?
Autosomal recessive osteopetrosis type 1 (ARO1), caused by harmful genetic changes (mutations) in the TCIRG1 gene, is a disorder that causes abnormal bone formation. In most cases, symptoms of the condition first appear in infancy. Characteristic features include unusually dense bones; a high risk of bone fractures; a large head size (macrocephaly) with a prominent forehead (frontal bossing); growth deficiency; and dental problems. The abnormal bone present in the skull may also lead to compression of nerves in the face and head, resulting in vision impairment or blindness, hearing loss, and paralysis of the facial muscles. In addition, breathing and feeding difficulties may result from narrowing of the passageways connecting the nose and throat.
The abnormal bone formation in ARO1 also affects the bone marrow, which is important for blood cell formation and immune system function. Consequently, children with ARO1 may have a shortage of red blood cells (anemia); problems with immune system function that lead to an increased risk for infections; and enlargement of the liver and spleen (hepatosplenomegaly). In addition, some affected individuals may have seizures due to low blood calcium levels. Intellectual disability (usually mild to moderate) may result from recurrent seizures and/or brain abnormalities that may occur in some individuals with ARO1.
How common is Autosomal Recessive Osteopetrosis Type 1?
The incidence of autosomal recessive osteopetrosis (ARO) is 1 in 250,000 individuals. About 50 percent of ARO cases are attributed to ARO1. ARO is more common in certain populations, including the Chuvash and Mari populations of Russia (1 in 3,500 and 1 in 14,000 individuals, respectively), the Middle East, the Swedish province of Västerbotten, and Costa Rica.
How is Autosomal Recessive Osteopetrosis Type 1 treated?
The treatment for ARO1 is primarily supportive. Patients are monitored, and symptoms are treated as they arise. Medical management typically includes blood transfusions and the treatment of fractures, infections, vision and hearing problems, and seizures if they develop. In addition, certain medications may slow the progression of the disease in some individuals. The only known cure for ARO1 is a bone marrow transplant early in life.
What is the prognosis for an individual with Autosomal Recessive Osteopetrosis Type 1?
Generally, the prognosis for children with ARO1 is poor. Most children with the condition die within the first decade of life, although early bone marrow transplants can be curative if they are successful.