A child presented with polyuria, polydypria, fever, clinical features of rickets, slit lamp examination shows the following,what is the probable diagnosis?
**Core Concept**
The question is testing the diagnosis of a rare genetic disorder that affects phosphate reabsorption in the kidneys, leading to rickets, polyuria, and polydipsia. This disorder is caused by a mutation in the SLC34A1 gene, which encodes a sodium-phosphate cotransporter in the proximal convoluted tubule.
**Why the Correct Answer is Right**
The correct answer is a case of hereditary hypophosphatemic rickets with hypercalciuria (HHRH), a rare genetic disorder characterized by impaired phosphate reabsorption in the kidneys, leading to hypophosphatemia, hypercalciuria, and rickets. The disease is caused by a mutation in the SLC34A1 gene, which results in decreased expression of the sodium-phosphate cotransporter type IIa (NaPi-IIa). This leads to increased phosphate excretion in the urine, decreased phosphate reabsorption in the kidneys, and subsequent hypophosphatemia. The increased phosphate excretion also leads to increased calcium reabsorption, resulting in hypercalciuria.
**Why Each Wrong Option is Incorrect**
**Option A:** This option might be a distractor for a similar condition, but it is not the correct answer. The condition described in option A is more likely to be X-linked hypophosphatemia, a different genetic disorder that also affects phosphate reabsorption in the kidneys. However, X-linked hypophosphatemia is caused by a mutation in the PHEX gene, not the SLC34A1 gene.
**Option B:** This option is a distractor for a condition that affects calcium reabsorption in the kidneys, not phosphate reabsorption. The condition described in option B is more likely to be familial hypocalciuric hypercalcemia (FHH), a genetic disorder that affects calcium reabsorption in the kidneys and leads to hypercalcemia.
**Option C:** This option is a distractor for a condition that affects vitamin D metabolism, not phosphate reabsorption. The condition described in option C is more likely to be vitamin D-dependent rickets, a genetic disorder that affects vitamin D metabolism and leads to rickets.
**Option D:** This option is a distractor for a condition that affects the kidneys' ability to concentrate urine, not phosphate reabsorption. The condition described in option D is more likely to be nephrogenic diabetes insipidus, a genetic disorder that affects the kidneys' ability to concentrate urine and leads to polyuria and polydipsia.
**Clinical Pearl / High-Yield Fact**
The SLC34A1 gene is a sodium-phosphate cotransporter that plays a crucial role in phosphate reabsorption in the kidneys. Mutations in this gene can lead to impaired phosphate reabsorption, resulting in hypophosphatemia and rickets.
**Correct Answer:** C.