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A 3-year-old girl is brought to the pediatrician for evaluation of decreased hearing in the left ear. The symptoms started 2 months ago and have progressively worsened. Her parents state she has difficulty hearing voices and sounds coming from her left. Past medical history is notable for a femoral fracture, which she sustained after falling from standing-height. There is no history of similar symptoms in her family members. The patient’s older sister was recently diagnosed with multiple sclerosis at the age of 20. Temperature is 37.3°C (99.1°F), blood pressure is 110/65 mmHg, and pulse is 87/min. The patient is below the 5th percentile for height and weight. Physical examination is notable for hepatosplenomegaly and sensorineural hearing loss in the left ear. Genetic testing reveals a homozygous mutation in the carbonic anhydrase type II gene (CA2). Which of the additional findings will most likely be present on laboratory testing?  

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Bone marrow transplant

osteopetrosis p. 473

Cranial nerve palsies

osteopetrosis p. 473

Osteoclasts p. 473

osteopetrosis p. 473

Osteopetrosis p. 473, 473

Pancytopenia p. 429

osteopetrosis and p. 473


Osteopetrosis, literally means "stone bone". It is an extremely rare genetic disorder whereby the bones harden and become denser. Despite this excess bone formation, people with osteopetrosis tend to have bones that are more brittle than normal.

People with osteopetrosis may present with impaired growth, frequent osteomyelitis (bone infections), vision and hearing impairment due to scleroses of skull bone and cranial nerve impingement or compressions, and neurological problems, such as weakness or numbness in the arms and legs. Treatment may include medications to increase bone density, surgery to remove bone, or to correct problems related to compression and neurovascular impingement.


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