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A 27-year-old female with nephropathic cystinosis was seen with long-standing but slowly progressive pancytopenia. She had had renal failure since childhood with two previous renal transplants and was on haemodialysis. She had always been mildly cytopenic with a platelet count of 80–90 × 109/l and mild normocytic anaemia. She had had undergone a bone marrow aspirate at the age of 7 years, which was non-diagnostic. Over the previous few years her platelet count had fallen to 30–50 × 109/l, neutrophils to 1·2–1·4 × 109/l and haemoglobin to 8–9 g/dl. Elucidation of the cause of pancytopenia was necessary as part of the consideration of her suitability for a third renal transplant. She therefore underwent a bone marrow aspirate and trephine biopsy. These revealed a normocellular but slightly disorganised marrow with adequate trilineage maturation and no increase in fibrosis. However, scattered throughout the aspirate smear, and in a patchy distribution in the trephine biopsy sections, were macrophages packed with irregular, colourless crystals of varying shapes and sizes showing birefringence under polarized light, consistent with cystinosis.

Cystinosis is a rare, autosomal recessive metabolic disease caused by a defect in the transport of cystine out of lysosomes, causing accumulation of intracellular, intra-lysosomal cystine crystals in various tissues. In the nephropathic type, accumulation is seen in many organs but the renal tubular cells are particularly vulnerable. Patients present with renal failure in infancy (most severe and most common variant) or early childhood. There is also a non-nephropathic, ‘benign’ type which primarily affects the cornea and presents in middle age with photophobia. These patients can also have bone marrow involvement but are rarely symptomatic.

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