**Core Concept**
Renal glycosuria is a rare condition characterized by the excessive excretion of glucose in the urine, despite normal blood glucose levels. This condition is caused by a defect in the reabsorption of glucose in the proximal convoluted tubule of the kidneys.

**Why the Correct Answer is Right**
The correct answer involves a defect in the sodium-glucose cotransporter 2 (SGLT2), which is responsible for the reabsorption of glucose in the proximal convoluted tubule. Normally, SGLT2 transports glucose from the filtrate into the renal tubular cells, where it is then reabsorbed into the bloodstream. In renal glycosuria, this process is impaired, leading to the excessive excretion of glucose in the urine. This condition is often associated with a mutation in the SLC5A2 gene, which codes for SGLT2.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct enzyme involved in renal glycosuria.
**Option B:** This option is incorrect because it refers to a different condition, Fanconi syndrome, which is characterized by the excessive excretion of glucose, amino acids, and other substances in the urine due to a defect in the proximal convoluted tubule.
**Option C:** This option is incorrect because it refers to a different condition, diabetes mellitus, which is characterized by high blood glucose levels due to impaired insulin secretion or insulin resistance.

**Clinical Pearl / High-Yield Fact**
Renal glycosuria is often asymptomatic and may be discovered incidentally during routine urinalysis. It is essential to rule out other conditions that cause glycosuria, such as diabetes mellitus, before making a diagnosis of renal glycosuria.

**Correct Answer:** C. SGLT2