Well, it turns out it's a genetic abnormality. So instead of sequencing a specific polypeptide chain, we sequence a slightly different polypeptide chain. And in the case of sickle cell anemia, there's a single substitution of a single amino acid in the beta subunit of the hemoglobin molecule. So instead of synthesizing glutamate at the 6th position, we synthesize valine at that 6th position. And the problem is the properties of these two amino acids is different. The properties of this one is that of a polar molecule.