A couple has a child diagnosed with achondroplasia. Neither parent has the condition. What is the most likely genetic mechanism for this child's disease?

✓ Correct Answer: Option D

Achondroplasia is an autosomal dominant disorder, but approximately 85% of cases arise from a de novo mutation in the FGFR3 gene. This means the mutation occurred spontaneously in the child, and neither parent carries the affected allele.