Thus far, all of the mutations in the SMARCA4 gene related to Coffin-Siris syndrome have arisen spontaneously. In other words, they were not inherited from a parent.
The chance of recurrence for future pregnancies is considered low (probably <1%).
Children of patients with a SMARCA4 change would have a 50% probability of inheriting the mutation. We cannot predict the degree in which they will be affected by this mutation.