Co-occurrence of both maternally inherited neurofibromatosis type 1 and Lesch-Nyhan disease in a child with severe neurodevelopmental impairment

Lesch-Nyhan disease (LND) is a rare X-linked recessive inherited purine metabolic disorder that accompanies neurodevel-opmental problems. Neurofibromatosis type 1 (NF1) is a relatively common autosomal dominant inherited genetic disorder characterized by tumors in various systems. Some children with NF1 also accompanies neurodevelopmental problems. Here, we describe a 5-year-old boy with a maternally inherited pathogenic variant in NF1 and hypoxanthine-guanine phos-phoribosyltransferase (HPRT ). He was referred for severe neurodevelopmental impairment and hyperuricemia. His mother was diagnosed with NF1 and the patient was also suspected of having NF1 because of cafe au lait macules. He had dystonia, rigidity, cognitive deficit, and speech/language impairment. Serum and urine uric acid concentrations were elevated. He had more severe neurodevelopmental delay than patients with only NF1, so his clinical symptoms could not be fully understood by the disease alone. To find the cause of his neurologic symptoms and hyperuricemia, the patient and his mother underwent a whole-exome sequencing test. As a result, the pathogenic variant c.151C>T (p.Arg51Ter) in HPRT1 was identified as hemi-zygote in the patient and heterozygote in his mother. The pathogenic variant c.7682C>G (p.Ser2561Ter) in NF-1 was identi-fied as heterozygotes in both of them. Although the clinical symptoms of both diseases were overlapping and complicated, genetic testing was helpful for accurate diagnosis and treatment. Therefore, we suggest to consider preemptive genetic evalu-ation if there are symptoms not sufficiently explained by known existing diseases. And it is considered valuable to review this rare case to understand the clinical course and possible synergic effects of these diseases.