A 23-year-old woman is brought to the ER because of a 1-hour history of severe pain and coldness of her left leg. History taking indicates that she dropped out of high school in the 10th grade due to difficulty with comprehension. Intelligence testing demonstrated her IQ to be 80 at that time. Her parents and 2 older siblings have normal intelligence and have no history of these symptoms. Ophthalmologic examination shows a partially dislocated lens in the right eye. Physical examination shows mottling and loss of pulses in the left lower extremity and foot. Arteriography of the left lower extremity shows thrombosis of the femoral artery. This patient most likely has a metabolic disorder involving which of the following amino acid?

Question

Quizplus · Accepted Answer

The symptoms and findings suggest homocystinuria, a disorder involving the metabolism of homocysteine. This condition can lead to thromboembolic events, lens dislocation, and developmental delays.  Homocystinurias represent a family of inherited disorders resulting from defects in several of the genes involved in the conversion of methionine to cysteine. These disorders result in elevated levels of homocysteine, metabolites of homocysteine, and methionine in the urine. Homocystinuria is often associated with mental retardation, although the complete syndrome is multifaceted and many individuals with this disease are mentally normal, while others experience variable levels of developmental delay along with learning problems. Common symptoms of homocystinuria are dislocated optic lenses, osteoporosis, lengthening and thinning of the long bones, and an increased risk of abnormal blood clotting (thromboembolism).

A 23-Year-Old Woman Is Brought to the ER Because of a 1-Hour