The application of exome-sequencing once more revealed to be a straightforward approach to the genetic diagnosis in a case with a complex phenotype partially overlapping with different syndromes and suggests that, in case of suspected Rubinstein–Taybi syndrome with negative results for mutations in CREBBP and EP300 genes, the screening of OTUD6B should be performed and its associated syndrome (intellectual developmental disorder with dysmorphic facies, seizures, and distal limb anomalies; IDDFSDA, OMIM#617452) should be included as a differential diagnosis. Here, EP300 is linked to intellectual developmental disorder with dysmorphic facies, seizures, and distal limb anomalies.