Nonsense mutations

These are mutations in which a mutation in the genetic code results in a change in the amino acid code such that a ‘STOP’ signal is generated, stopping any further production of the protein after this signal.

What a nonsense 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 amino acids are generated. In this case, there is usually no functional protein produced. This would lead to a loss of activity.

Example 2: If a mutation occurs near the end of the protein sequence, 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 the loss of a crucial part 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.