CFTR and cystic fibrosis: Nearly 70–90% of the CF patients carry the allele F508, where phenylalanine at position 508 (F508del CFTR) in the NBD1 domain of the protein is lost leading to misfolding of the protein causing the most severe defect, that is the mistrafficking of CFTR protein that remains trapped in the endoplasmic reticulum and is subsequently degraded, before reaching the membrane.