The syndrome is caused by an error in the FOXP1 gene, which is located on chromosome 3. The error can be caused by several mechanisms, including:
- the deletion of the whole gene (and frequently also other genes besides FOXP1),
- deletion of a part of the gene,
- errors causing disruption or premature termination of the correct code and
- spelling errors in the FOXP1 gene.
Almost all known pathogenic variants arose de novo, which means that they are absent in both parents but present in all cells of the child. In case a FOXP1 pathogenic variants is not found in the parents, brothers or sisters without any signs of the disorder do not need to be tested. Future brothers and sisters of a patient with a de novo FOXP1 pathogenic variant have a very low recurrence risk (<1%).