Gene Therapy Would Not Be an Effective Treatment for Down

Gene therapy would not be an effective treatment for Down syndrome because

A) scientists do not know which faulty genes cause the syndrome.
B) Down syndrome results from having an extra chromosome with over a thousand genes.
C) liposomes and nasal sprays cannot be used due to abnormalities in the respiratory tract of Down syndrome individuals.
D) Down syndrome is not a genetic disorder.
E) the gene therapy treatment could not be performed on an adult individual.