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Nephropatic cystinosis (NC) is a rare disease associated with pathogenic variants in the CTNS gene, with a common variant that consists of a 57kb-deletion involving CTNS. Patients with NC that are treated with cysteamine improve their life quality and expectancy. We report a 12-month-old girl with a poor growth rate since the 4th month of life. She was admitted to the Hospital with acute kidney injury, severe dehydration and metabolic acidosis. She was treated with volume restorative and bicarbonate. Proximal tubulopathy and Fanconi's syndrome was diagnosed. Medical treatment improved renal function that was stabilized in stage 4 chronic kidney disease (CKD). Since infantile NC was suspected, CTNS genetic analysis was considered. Genomic DNA was isolated from peripheral blood to perform PCR for exons 3-12 in CTNS gene and for the specific 57kb-deletion PCR. Afterwards, variant segregation analysis was performed in the familiar trio. The genetic analysis showed that the patient was homozygous for the common 57kb-deletion encompassing CTNS that had been inherited from her asymptomatic heterozygous parents. The molecular confirmation allowed genetic counselling for parents and facilitated the access to cysteamine. Oral treatment with cysteamine resulted in improvement of renal function to CKD stage 3. After 16 months of treatment the patient shows metabolic stability and mild recovery of height. Ophthalmologic follow-up detected ocular cystine crystals 12 months after diagnosis, starting cysteamine drops.

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Background Cystinosis is a rare disease caused by CTNS gene defects. The main clinical presentations are nephropathic infantile cystinosis (NIC) and nephropathic juvenile cystinosis (NJC); both develop chronic kidney disease (CKD) and extrarenal complications. Opportune diagnosis and access to therapy are challenging in developing countries. Methods To describe the clinical and genetic profile in all cystinosis patients known to be diagnosed in Chile, we performed a retrospective review of the medical records of those patients diagnosed from 1994 to 2022. Age at diagnosis, glomerular filtration rate, metabolic variables, anthropometric values, access to treatment, outcomes, and genetic results were analyzed. Results Nine patients (8NIC/1NJC) were diagnosed. Patients with NIC had a median age of 16.5 (IQR 13-23) months at diagnosis, and two patients died during follow-up. Most of the patients started cysteamine therapy up to 5 months after diagnosis and reached CKD stages 3-4 within four years. During the follow-up, all but one of the NIC patients showed height for age Z-score values between -1.5 and -4.0. Two patients received kidney transplants, and one of them remains functional after 15 years. The single NJC was a 21-year-old female patient who received irregular cysteamine therapy and rapidly reached CKD stage 5. Genetic testing was positive in 7/7 cases, being del57kb the predominant variant (10/14 alleles). Conclusions Developing countries face many challenges in providing adequate healthcare. Our findings show clinical and diagnostic aspects to the medical and patient community that might contribute to the diagnostic approach and treatment access for cystinosis in Chile. Opportune genetic testing may facilitate early diagnosis that is known to be associated with a better prognosis.

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