WHSUS is caused by an error in the gene POGZ. POGZ is expressed in the fetal and human brain and is crucial for human brain development and functioning. Mostly, the mutations are detected with a broad genetic test covering many genes that are involved in syndromes with developmental delay/intellectual disability (exome sequencing). It concerns mostly a new mutation, that means that it occurred spontaneously in the patient and was not inherited from the father nor the mother. In that case brothers or sisters without any signs of the disorder do not need to be tested.