What is the metabolic defect in Primary Oxaluria Type II?
**Core Concept**
Primary Oxaluria Type II (POC II) is a rare genetic disorder characterized by the excessive production of oxalate, a key component of kidney stones. The underlying metabolic defect involves a deficiency in the enzyme glyoxylate reductase (GRHPR).
**Why the Correct Answer is Right**
The enzyme GRHPR is responsible for converting glyoxylate to glycolate, thereby preventing the production of oxalate. In POC II, the GRHPR enzyme is either deficient or dysfunctional, leading to the accumulation of glyoxylate and subsequent increased production of oxalate. This results in the formation of calcium oxalate stones in the kidneys and potentially other complications.
**Why Each Wrong Option is Incorrect**
**Option A:** This option would be incorrect as Primary Oxaluria Type I (POC I) is caused by a deficiency in the enzyme alanine-glyoxylate aminotransferase (AGXT), not GRHPR.
**Option B:** This option would be incorrect as Primary Hyperoxaluria Type III (PH III) is caused by a deficiency in the enzyme 4-hydroxy-2-oxoglutarate aldolase (HOGA1), not GRHPR.
**Option C:** This option would be incorrect as the metabolic defect in POC II is specific to the GRHPR enzyme, and not a general defect in glyoxylate metabolism.
**Clinical Pearl / High-Yield Fact**
Primary Oxaluria Type II is a rare but significant cause of nephrolithiasis, and identifying the underlying metabolic defect is crucial for appropriate management and treatment.
**Correct Answer: D. GRHPR. Glyoxylate reductase (GRHPR) deficiency.**