Features of cystinuria are
**Core Concept**
Cystinuria is a genetic disorder characterized by the abnormal reabsorption of cystine and other dibasic amino acids (lysine, arginine, and ornithine) in the kidneys. This leads to the formation of cystine stones in the urinary tract.
**Why the Correct Answer is Right**
Cystinuria is caused by mutations in the SLC3A1 and SLC7A9 genes, which encode proteins involved in cystine and dibasic amino acid transport in the kidneys. The impaired reabsorption of cystine results in its increased excretion in the urine, where it can form stones. The disease is inherited in an autosomal recessive pattern, meaning that affected individuals are homozygous for the mutated gene.
**Why Each Wrong Option is Incorrect**
**Option A:** Cystinuria is not typically associated with the formation of oxalate stones.
**Option B:** While cystinuria can increase the risk of kidney stones, it is not directly linked to the development of kidney cancer.
**Option C:** Cystinuria is not caused by a deficiency of the enzyme cystinase.
**Clinical Pearl / High-Yield Fact**
Cystinuria is a classic example of a genetic disorder that affects the transport of specific amino acids in the kidneys, leading to the formation of stones. It is essential to consider this condition in patients with recurrent kidney stones, particularly those with a family history of the disease.
**Correct Answer: D.**