It is a single base change in the sixth codon of the beta globin gene that changes a glutamate to a valine. Frameshift mutations alter the reading frame by inserting or deleting any number of bases that are not divisible by three. Nonsense mutations change an amino acid coding codon to become a stop codon. Promoter defects alter the signals that control the translation of a gene. Insertion mutations in the human genome often occur when transposable elements like Alu and LINE sequences insert into genes.
Silent mutations are change in DNA sequence that have no phenotypic consequence.
We have lots of these types of changes, often referred to as polymorphisms. They are good for forensic purposes to distinguish among us. Missense in the beta globin gene are called hemoglobinopathies. The best example being sickle cell. Frameshift, nonsense, promoter, splicing and deficiency mutations have been discovered in the beta globin genes and are classified as thalassemias.