Here we present an adult patient with developmental delay, trigonocephaly, speech impairment and ID who was diagnosed as Opitz C syndrome early in life, in whom we have identified by WES a novel splicing mutation in the FOXP1 gene and provide a detailed clinical description, in comparison to so far reported patients identified carrying deleterious FOXP1 mutations. This evidence concerns the gene FOXP1 and trigonocephaly.