The wor indel is a portmanteau of insertion or deletion, referring to the two types of genetic mutation that are often considered together because of their similar effect and the inability to distinguish between them in a comparison of two sequences. In coding regions of the genome, unless the length of an indel is a multiple of 3, they produce a frameshift mutation. The most common mutation causing cystic fibrosis in the cystic fibrosis transmembrane receptor (CFTR) gene is a deletion of three bases encoding phenylalanine at position 508 of the protein (ΔF508, or p. F508del).