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Cystinosis Fanconi Syndrome Paediatric — ESENeph MCQ

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HardTubular DisordersCystinosis Fanconi Syndrome PaediatricESENeph

A 5-year-old boy presents with failure to thrive, polyuria, polydipsia, and rickets. Bloods: phosphate 0.5 mmol/L, calcium 2.20 mmol/L, bicarbonate 24 mmol/L, glucose normal. Urine: glycosuria (blood glucose normal), aminoaciduria, phosphaturia, tubular proteinuria. Renal ultrasound is normal. What is the most likely diagnosis?

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Correct answer: C — Cystinosis

The combination of renal phosphate wasting (hypophosphataemia), normoglycaemic glycosuria, generalised aminoaciduria, and tubular proteinuria constitutes the renal Fanconi syndrome — a global proximal tubular dysfunction. In a young child with failure to thrive and rickets, the most common cause of Fanconi syndrome is infantile nephropathic cystinosis, an autosomal recessive lysosomal storage disease caused by CTNS gene mutations. Cystine crystals accumulate in lysosomes throughout the body. Diagnosis is confirmed by elevated leucocyte cystine levels. Oral cysteamine therapy slows disease progression. Without treatment, ESKD typically occurs by age 10.

Reference: Nesterova & Gahl 2017 – Cystinosis; JRCPTB 2022 – Nephrology Curriculum