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A 1-year-old with failure to thrive has polyuria, rickets, and Fanconi syndrome (glucosuria, aminoaciduria, phosphaturia). Slit-lamp exam reveals corneal cystine crystals.
AR; CTNS (cystinosin - lysosomal cystine transporter)
- Lysosomal cystine accumulation
- Renal: Fanconi syndrome → renal failure (childhood)
- Ocular: Corneal cystine crystals (photophobia)
- Growth: Failure to thrive, rickets
- Other: Hypothyroidism, diabetes, CNS involvement (late)
- Elevated leukocyte (white blood cell) cystine level is the diagnostic standard
- Slit-lamp exam shows corneal cystine crystals
- CTNS molecular testing confirms (common 57-kb deletion plus sequencing)
- Renal Fanconi syndrome on labs supports the diagnosis in infancy
- Cysteamine (depletes lysosomal cystine)
Cystinosis vs. cystinuria: CystinOSis = One AA (cysteine) Stuck in the lysOSome, which causes multi-system disease (as lysosomal storage diseases do). It affects kidneys, eyes, and growth: "the whole OS" (operating system). "Cyt (sight)" in cystinosis: think photophobia from corneal crystals.
