A frameshift mutation is the result of the addition or deletion of nucleotides.
A frameshift mutation is often a more damaging mutation than a point mutation. It can result in changing virtually every amino acid in a protein.
If a mutation results in a cytosine base being inserted into the sequence TAT CCG TCG ACG TAC, the sequence will be read completely differently: TCA TCC GTC GAC GTA C.
Every single amino acid after the point of mutation changes because the codons are altered.
Tay-Sachs disease, which affects the nervous system, is a frameshift mutation which is caused by a four base insertion.
Not all insertion and deletion mutations result in a frameshift. If the insertion or deletion is a multiple of three, there will be no frame shift.
This is because the change still allows the codons after the mutation to be read properly.