Frameshift mutations

These are mutations in which insertion or deletion of one or more DNA bases results in a change in all of the amino acid code that occur after the mutation.

What a frameshift mutation means in terms of disease depends very much on where the mutation occurs. 

Example 1: If a mutation occurs early on in the sequence of the protein, then little or no of the original protein is generated. This would lead to a loss of activity.

Example 2: If a mutation occurs near the end of the protein sequence which results in a slightly earlier stop codon, then most of the amino acids required are present and somewhat normal folding can occur. This could lead to a reduction in activity, but some normal function can still be carried out.

Example 3: If a mutation occurs near the end of the protein sequence but results in a gain of amino acids which disrupt the normal folding of the protein this could prevent it from interacting with other proteins required to carry out its normal function. This would lead to a loss of activity.