Coffin-Siris Syndrome (BAF Complex)

A 3-year-old boy is brought to the pediatric clinic with developmental delay, coarse facial features, and hypoplasia of the fifth digit nails. His parents are healthy and unrelated, with no family history of similar conditions. Genetic testing confirms a heterozygous de novo mutation in ARID1B. The inheritance pattern marked **A** in the pedigree diagram shows the characteristic presentation of Coffin-Siris Syndrome. Which of the following best describes the inheritance pattern and recurrence risk for this family?