Ease Into Prep with a USMLE^® Step 2 CK Question of the Day

The correct answer is E. This patient has Alport syndrome, also known as hereditary nephritis. This diagnosis should be suspected on the basis of an X-linked inheritance of hematuria, sensorineural deafness, and lenticonus. Lenticonus (a localized, cone-shaped deformation of the lens surface) can occur without nephritis and is pathognomonic of the disease. The hematuria progresses to nephritis and may cause renal failure in late adolescence in affected males. Patients who have Alport syndrome have a defect in the genes encoding the chains responsible for formation of type IV collagen. Most of the patients have a defect in the alpha-5 chain. Others have a defect in alpha-3 or alpha-4 chains.

Patients who have a strong clinical suspicion of Alport syndrome should first get a skin biopsy done. Immunohistochemical analysis of skin is done using a monoclonal antibody against the alpha-5 chain. If there is no expression of this protein on a skin biopsy, a diagnosis of Alport syndrome is confirmed.

A kidney biopsy (choice C) is done only if the results of the skin biopsy are equivocal.

The patient has established sensorineural hearing loss and anterior lenticonus. Audiologic testing (choice A) and eye examination (choice D) only confirm these. They would not be helpful in confirming the diagnosis of Alport syndrome.

Patients who have Alport syndrome typically have no abnormalities in the brain or gastrointestinal tract. It is unlikely that a CT scan of the head (choice B) or an upper gastrointestinal endoscopy (choice F) would be helpful.