 FOXG1 syndrome is a rare genetic condition caused by mutations in the FOXG1 gene. It is characterized by intellectual disability, delayed motor skills, and seizures. This study examined the clinical spectrum of FOXG1 syndrome and found that individuals with missense variants had a milder phenotype than those with gene deletions or nonsense variants. Additionally, individuals with missense variants were more likely to achieve independent walking than those with gene deletions or frameshift variants. Furthermore, truncation mutations preserving the forkhead DNA binding domain were associated with better developmental outcomes. This article was authored by Elise Brimble, Catherine G. Reyes, Copaca Cajatas, and others.