De novo monoallelic mutations in SCN2A are an increasingly recognised cause of an early-onset seizure and developmental delay.16 Despite its identification in 2001, testing of the gene has only become widely available with the advent of next-generation sequencing.17SCN2A was the most frequently mutated gene in our series, accounting for 11 of 71 mutations and 3% of the series overall (figure 1 and table 2). The gene discussed is SCN2A; the disease is Global developmental delay.