What Did Scientists Discover Was the Primary Cause for Genetically

What did scientists discover was the primary cause for genetically controlled language disorder connected to language ability in other species?

A) The cause was one mutation in a single gene on one chromosome.
B) The disorder was not inherited but related to diet.
C) Affected family members were lacking vocal chords.
D) The cause was multiple mutations in multiple genes on one chromosome.
E) The cause was multiple mutations in multiple genes on many chromosomes.