Would a Mutation in an Intron Affect Gene Expression?

The intron sequences that affect mRNA accumulation are redundant and dispersed, so a point mutation or even a large deletion in the intron would probably not significantly reduce the expression of the gene unless splicing was disrupted.

How might a mutation in an intron affect the expression of a gene?

If the intronic alterations are in the regulatory regions, these could affect gene expression levels. Instead if the mutations are in splice sites, protein truncation or non-functional protein could be the result. The phenotype of these alterations depends on how important is the affected proteins or expression levels.

Do mutations in introns matter?

Introns occupy about 40% on average of the total length of genes, which means that most randomly occurring mutations will fall into intron regions, and do not affect protein sequences and functions.