Although 90% of pwCF are eligible for CFTR modulator therapy and eligible patients can start ETI early in life, potentially avoiding chronic lung disease development, there are (1) 10% of patients, who are not eligible; (2) patients, who started on HEMT but did not tolerate it; and (3) patients who already have significant CF-related disease and having recurrent infections being colonised with CF-related pathogens. This evidence concerns the gene CFTR and chronic lung disease.