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Cystinuria Type A SLC3A1 Inheritance — ESENeph MCQ

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HardRenal Stone DiseaseCystinuria Type A SLC3A1 InheritanceESENeph

A 23-year-old woman presents with recurrent renal colic. Stone analysis shows pure cystine. Her 24-hour urine shows cystine excretion of 2500 umol/day (markedly elevated). Genetic testing shows biallelic SLC3A1 mutations. Her brother is affected but parents are unaffected. What is the inheritance pattern of her condition?

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Correct answer: A — Autosomal recessive (Type A cystinuria)

Cystinuria is classified by genotype: Type A involves biallelic SLC3A1 mutations (chromosome 2p) with autosomal recessive inheritance — heterozygous carriers have normal urine cystine. Type B involves biallelic SLC7A9 mutations (chromosome 19q) with autosomal recessive inheritance, though SLC7A9 heterozygotes may show mild cystine elevation. The unaffected parents and affected sibling pattern confirms autosomal recessive inheritance (Type A). Cystinuria is the commonest inherited cause of renal stones, caused by defective reabsorption of dibasic amino acids (cystine, ornithine, lysine, arginine — COLA mnemonic) in the proximal tubule and intestine.

Reference: Dello Strologo et al 2002 – Cystinuria Classification; EAU 2023 – Urolithiasis Guidelines