Infantile Nephropathic Cystinosis - Homozygous c.516dupC Mutation of the CTNS Gene

Abstract

Objective: Cystinosis is a rare, autosomal recessive, lysosomal storage disorder characterized by cystine accumulation throughout the body, due to mutations in the gene encoding cystinosin, named CTNS. Infantile nephropathic cystinosis (INC), the most severe form of the disease and the most common cause of renal Fanconi syndrome (FS), starts with proximal tubulopathy and causes renal failure and various extra-renal manifestations over the time. Case Presentation: The authors report a 15-month-old boy of Greek origin who presented with failure to thrive over the last 7 months and was noted to have decreased weight and short stature. The metabolic control showed normoglycemic glucosuria, significant proteinuria, and generalized aminoaciduria, suggesting FS. Sequencing analysis of the CTNS gene revealed the frameshift mutation c.516dupC in the homozygous state, confirming the diagnosis of INC. Only one compound heterozygous individual for this mutation has been reported before. Conclusion: The index case brings out a new correlation of the c.516dupC mutation in the homozygous state with a pure INC phenotype. Alongside, it reminds clinicians to consider cystinosis in the differential diagnosis of failure to thrive or short stature.