Abnormality in Renal tubular acidosis with rickets is:
**Core Concept**
Renal tubular acidosis (RTA) is a condition characterized by the kidneys' inability to regulate acid-base balance, leading to metabolic acidosis. Type 1 RTA (distal RTA) is further complicated by the presence of hypokalemia, alkalosis, and rickets due to impaired calcium reabsorption in the distal convoluted tubule.
**Why the Correct Answer is Right**
The correct answer is related to the abnormality in calcium reabsorption in the distal convoluted tubule. In Type 1 RTA, there is a defect in the function of the thiazide-sensitive Na-Cl cotransporter, leading to decreased calcium reabsorption and increased urinary excretion of calcium. This results in hypocalcemia, which in turn causes rickets in children. The primary mechanism involves impaired calcium reabsorption in the distal convoluted tubule, which is mediated by the paracellular pathway.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specifically address the relationship between RTA and rickets. While hypokalemia is a feature of Type 1 RTA, it is not the primary cause of rickets.
**Option B:** This option is incorrect as it refers to a feature of Type 2 RTA (proximal RTA), which is characterized by impaired bicarbonate reabsorption in the proximal convoluted tubule.
**Option C:** This option is incorrect as it refers to a feature of hypophosphatemic rickets, a condition characterized by defective phosphate reabsorption in the proximal convoluted tubule.
**Clinical Pearl / High-Yield Fact**
Remember that Type 1 RTA is often associated with other electrolyte imbalances, such as hypokalemia and hypocalcemia, which can exacerbate the clinical presentation of rickets.
**Correct Answer: A. Impaired calcium reabsorption in the distal convoluted tubule.**