WBR0279
| Author | [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Edited by Alison Leibowitz)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::A 55-year old male with a history of diabetes and hypertension presents to the physician’s office regarding a progressive loss of vision. Upon pysical examination, the blood pressure is 160/90 mm Hg and the pulse is 90 beats per minute. Laboratory findings include a blood glucose level of 160 mg/dl. An eye examination confirms the presence of bilateral cataracts. The presence of which of the following substances is the most likely cause of the patient’s vision loss?]] |
| Answer A | AnswerA::Fructose |
| Answer A Explanation | AnswerAExp::Fructose accumulation causes essential fructosuria which would result due to the deficiency of fructokinase. It is a benign condition that is most often asymptomatic |
| Answer B | AnswerB::Sorbitol |
| Answer B Explanation | AnswerBExp::See explanation |
| Answer C | AnswerC::Galactose |
| Answer C Explanation | AnswerCExp::Galactose accumulation would result as a result of galactokinase deficiency and galactose appears in blood and urine and may cause infantile cataracts. It is a relatively mild condition |
| Answer D | AnswerD::Galactitol |
| Answer D Explanation | [[AnswerDExp::Galactitol accumulation is due to the deficiency or the absence of the enzyme galactose-1-phosphate uridyltransferase, which causes galactosemia, an autosomal recessive disorder with symptoms such as failure to thrive, jaundice, hepatomegaly, infantile cataracts and mental retardation.]] |
| Answer E | AnswerE::Glycogen |
| Answer E Explanation | AnswerEExp::Intracellular accumulations of glycogen would lead to abnormal glycogen metabolism and could lead to a group of disorders called glycogen storage diseases |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::In glucose metabolism, an alternative method of trapping glucose in the cell is its conversion to sorbitol by the enzyme aldose reductase. In diabetics, the accumulation of sorbitol increases the risk for osmotic damage, ultimately resulting in cataracts.
Educational Objective Tissues lacking sorbitol dehydrogenase are at risk for intracellular sorbitol accumulation seen in diabetics with chronic hyperglycemia. Reference: First AID for the USMLE Step 1 2011 Pgs 104, 110 |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |