RecruitingRare CFTR Mutation Cell Collection Protocol (RARE)Over 1,900 mutations in the gene for the cystic fibrosis transmembrane conductance regulator (CFTR) protein are implicated in causing Cystic Fibrosis (CF). Potential therapies that directly target defective CFTR are being evaluated in important clinical trials, but most target the most common CFTR mutation F508del. Many patients with rare CF mutations are not able to participate in those studies. The RARE study is specifically designed for people with CF caused by rare mutations. Eligible rare mutations are listed below: • CF patients who are heterozygous for pre-mature stop codons as noted below: i. one allele must be a F508del ii. the other allele must be a pre-mature stop codon mutation • CF Patients with other genotypes that require Study PI permission: i. CF patients with two mutations that are not eligible for Trikafta ii. CF patients homozygous or heterozygous (other allele must be F508del) for rare mutations of special interest (e.g., 711+3A-\>G, 2789+5G-\>A, 3272-26A-\>G, 3849+10kbC-\>T). Other rare mutations will be considered on a case by case basis This is a multi-site, specimen collection study. Investigators will collect blood, intestinal cells and nasal cells from each participant. Cells from these specimens will be used to test future CFTR modulators to see if they might work for people with study eligible rare mutations. Having cells to test in the lab is an important first step in identifying potential new therapies for people with these mutations.