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Objective:To explore the etiology, clinical diagnosis and treatment strategy of Lesch Nyhan syndrome.Methods:We retrospectively analyzed 2 patients with severe dyskinesia, mental retardation and complicated renal calculi who were admitted to the first people's Hospital of Zhengzhou in August 2019. Case 1, male, 9 years old, had multiple urinary calculi for 1 year. The patient came to the local hospital because double multiple kidney stones and bladder stonesa year ago. The patient had been treated with transurethral holmium laser lithotripsy for bladder stones. The results of infrared spectrum showed that the bladder stone was anhydrous uric acid stone. A week ago, color Doppler ultrasound showed multiple kidney stones and bladder stones. The patient was underdeveloped, mentally retarded and had a full-term cesarean section. There was no history of hypoxia, asphyxia and rescue of the patient. He had the following clinical manifestations: In the waking state, he was no language response to any stimulation. The nasolabial fold on the right was shallow and the corner of the mouth was oblique to the left. He lost the large movements such as lifting head, sitting alone, standing. The trunk showed torsion spasticity, limb muscle strength 2-3, limbs showing spastic hypertonia, limb joints stiff, hands showing fist-like, no involuntary movement and muscle fasciculation. The biceps reflex and knee tendon reflex were not elicited, and the pathological reflex was positive. Serum uric acid was 517 μmol/L. The Case 2 came from the same family, male, 6 years old, had the similar symptoms to his elder brother case 1. The family members complained on behalf of the child about intermittent fever for more than 2 years. The imaging examination of case 2 revealed kidney stones. Serum uric acid was 373 μmol/L. Whole Exome Sequencing and Sanger Sequencing were used to find the genetic causes of the two siblings. The NCBI-Homologene database was used to find the homologous sequence of the human HPRT1 gene, and the human HPRT1 gene sequence was compared with other species to analyze the protein conservation. The online website PredictProtein (http: //www.predactprotein) was used to predict the two-dimensional structure of the HPRT1 gene. The reported cases were summarized and same with the treatment plan.Results:A De novo mutation [c.571T>G(p.Tyr191Asp)] was found in the HPRT1 gene of the child, which was inherited from the mother. Lesch Nyhan syndrome can be diagnosed by the results of gene examination combined with clinical manifestations. The amino acid Tyr at the 191 position and the amino acids before and after it were highly conserved. Amino acid 191 was involved in the β-strand of the protein. We treated the patients with the lowest dose of allopurinol and children's conventional dose of potassium sodium bicitrate granules, and low purine diet. After 3 months of treatment, the serum uric acid was decreased, and the urinary calculi did not increase significantly.Conclusions:Combining with the clinical manifestations of children, HPRT1 gene might be the cause of pediatric disease and the two siblings could be diagnosed as Lesch-Nyhan syndrome. For such patients, the lowest dose of allopurinol and children's conventional dose of potassium sodium hydrogen citrate granule combined with diet could be more effective.