The mutation that causes sickle cell disease in humans is

Missense mutation

Explanation:

Missense mutation is a type of point mutation where a single nucleotide is changed to cause substitution of a different amino acid. This in turns render the resulting protein non-functional.

In the case of sickle-cell disease, the sixth amino acid in the gene sequence, glutamate (GAG) is substituted with valine (GUA), due to Adenine nucleotide changed to Uracil nucleotide. Thus, missense mutation has occurred