Cystinosis

• autosomal recessive lysosomal storage disease; defect in cystine transport across the lysosomal membrane resulting in widespread intralysosomal accumulation of cystine.
• CTNS gene located on chromosome 17p13
• cystine accumulates in the RE system, kidneys and other tissues.
• unlike cystinuria, stones do NOT occur in this condition
• presents in 1st year of life and have chronic progressive CKD >> ESRD by the age of 10

Features

• Fanconi syndrome (often with severe hypophosphatemia and consequent vit.D-resistant rickets)
• lymphadenopathy
• severe growth retardation
• CNS involvement
• insulin deficiency
• corneal opacities and photophobia
• cardiac conduction defects
• hypothyroidism
• BM failure

Dx -

corneal or conjunctival crystals usually suggest diagnosis, which can be confirmed by measuring the cystine content of neutrophils or cultured fibroblasts

Antenatal Dx by measuring cystine levels in chorionic villi or cultured amniotic fluid cells

Tx