WBR0279
| Author | [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [2])]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::A 72-year-old man with a history of type 2 diabetes presents to the physician’s office for progressive loss of vision. He explains that recently, he has been sensing that all lights are too bright and has been seeing halos around lights. His night vision has become much worse in the past few months, and he has been avoiding driving at night. His temperature is 36.6 °C (97.88 °F), his blood pressure is 136/80 mmHg, and his heart rate is 76/min. Laboratory findings are remarkable for a blood glucose level of 320 mg/dL and HbA1c of 9.9 mmol/mol. The accumulation of which substance is associated with the development of this patient’s progressive 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::Diabetic cataract is a common cause of blindness worldwide.
In glucose metabolism, an alternative method of trapping glucose in the cell is its conversion to sorbitol by the enzyme aldose reductase. In diabetics, augmented glucose levels result in the intracellular accumulation of sorbitol leading to osmotic damage in the form of cataracts. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Diabetes mellitus, WBRKeyword::Diabetes, WBRKeyword::Diabetes mellitus type 2 |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |