How would gene expression be affected if there was an error in translation (reading instructions) ?

Gene expression is about making mRNA which is then translated into a protein. If the mRNA that was expressed is mis-read it may or may not have an affect on gene expression. It will have a negative effect if:

1. The protein produced is required for gene expression (e. g. the DNA polymerase)

2. The protein produced is another critical protein that the cell cannot live without.

3. If the question is more about constantly misreading during translation, eventually the cell would die because the wrong proteins would be made (or not made at all).