Affiliations: Molecular Biology Laboratory, Human Genetics Department, National Institute of Pediatrics, Mexico City, Mexico | Inborn Metabolic Disorders and Metabolic Screening Laboratory, National Institute of Pediatrics, Mexico City, Mexico
Note:  Corresponding author: Ariadna González-del Angel, Laboratorio de Biología Molecular, Departamento de Genética Humana, 9° Piso de la Torre de Investigación “Joaquín Cravioto”, Instituto Nacional de Pediatría, Avenida Insurgentes Sur 3700-C, Colonia Insurgentes Cuicuilco, Delegación Coyoacán, CP 04530, México, Distrito Federal, Mexico. Tel.: +52 55 1084 0900 ext. 1306; Fax: +52 55 10 84 38 83; E-mail: [email protected]
Abstract: Classic nephropathic cystinosis (CNC) is an autosomal recessive and infrequent inborn metabolic disease that should be suspected in all children who show failure to thrive and renal Fanconi syndrome (RFS). Slit-lamp examination reveals pathognomonic corneal deposits of cystine crystals in virtually all affected individuals after 12–16 mo of age. A diagnosis of CNC is difficult to confirm in children living in Mexico and most Latin American countries, because cystine levels can be measured only at a few locations. We report the cystinosin genotype findings in 15 Latin American patients with a high clinical suspicion of CNC mainly due to RFS (n =13), although five of them lacked proper ophthalmologic assessment, despite being more than 1-year-old. Molecular analysis confirmed diagnosis of CNC in six (40%) of the 15 patients, five of them with RFS and cystine crystals. The remaining nine (60%) patients had a normal genotype. The predominance of a normal cystinosin genotype in eight of 13 patients with RFS (61.50%) reinforces the need to perform slit-lamp examinations in all patients with RFS over 1 yr of age, prior to measuring cystine or performing molecular cystinosin study, both methods not readily available throughout Latin America.