How Does This Study Support the Study of a Family

How does this study support the study of a family with a language disorder support the role of genes in communication?

A) The identification of a single mutation in a single gene responsible for the disorder
B) The disorder is common in the family
C) The family members were all lacking vocal chords
D) The identification of multiple mutations in multiple genes responsible for the disorder
E) The identification of the same mutation in all patients with speech disorders