A Case of Intellectual Disability without Epilepsy Associated with a Pathogenic Variant of STXBP1

The case concerns a 14-year-old boy with no specific history at birth, but with global developmental delays during childhood. He was unable to walk independently at 12 months and to say “mama” and “dada” until 2 years of age. Brain magnetic resonance imaging findings revealed minimal corpus callosum hypoplasia, and genetic tests for Fragile X syndrome and Prader-Willi syndrome were negative. There was no seizure history, and no epileptogenic foci were observed on EEG. In the metabolic work-up, mitochondrial dysfunction was suspected from a urine organ-ic acid test due to the presence of elevated levels of citric acid cycle intermediates such as ethyl-malonic acid, succinate, and citrate, and no patho-logic findings were found on muscle biopsy. I was diagnosed re-ceived