Aaron complains to his parents that he is experiencing significant pain in his right leg, and he does not have much of an appetite. Aaron's father takes him to the doctor for a thorough exam. After getting lab results, the doctor reports, "The pain is his leg is likely due to the presence of misshapen red blood cells." Of the following disorders, which is the most likely diagnosis of Aaron's condition?

A) Sickle-cell anemia
B) Down syndrome
C) Tay-Sachs disease
D) Klinefelter's syndrome