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Infantile nephropathic cystinosis: Clinical features and outcome

Background: Nephropathic infantile cystinosis, the most common cause of renal Fanconi syndrome, presents in early infancy with impaired growth, polyuria and polydipsia, and progresses to end stage renal disease during the first decade. Diagnosis is based on corneal examination for cystine crystals, leukocyte cystine content and genetic testing of the CTNS gene. Information on clinical features and genotype of Indian children with cystinosis is limited. Methods: We describe clinical features, renal outcomes and genetic variants in the CTNS gene in Indian children with cystinosis. Results: We included 19 patients with cystinosis from 17 families predominantly presenting with poor growth (95%), polyuria (84%) and refractory rickets (74%). Cystine crystals were present in 84%. Fanconi syndrome was common; two had nephrocalcinosis and 9 presented with eGFR <60 ml/ min/ 1.73 m2. Genetic analysis, performed in 11 families, (12 patients) showed 8 variants. Five were reported, pathogenic variants, one was likely pathogenic and two were rare or novel variants of unknown significance. Conclusion: The p.Thr7PhefsTer7 variant, common to five unrelated patients, might be a population hotspot. Eight (42%) patients have been initiated on therapy with cysteamine. Studies with prolonged follow-up are necessary to define renal and extrarenal outcomes and the effect of cysteamine in Indian children.