Disease severity of people with cystic fibrosis carrying residual function mutations: Data from the ECFS Patient Registry

People with cystic fibrosis carrying residual function (RF) mutations are considered to have a mild disease course. This may influence caregivers and patients on how intensive the treatments should be.Characterize disease severity of patients carrying RF mutations, using the European CF Society Patient Registry (ECFSPR) data.Demographic, clinical characteristics, lung function and death probability of patients carrying at least one RF mutation were analyzed and compared to patients homozygous to minimal function mutations (MF).Of the 44,594 eligible patients (median age 19.5 years, IQR 10-29.8), 6,636 (14.6%) carried RF mutations, and 37,958 (85.1%) MF mutations. Patients carrying RF mutations were older, diagnosed at a later age, had lower sweat chloride at diagnosis and better FEV1pp at each age group. However, their FEV1pp declined with age and rates of chronic Pseudomonas aeruginosa increased with age. A significant number of patients with RF had FEV1pp similar to patients with MF at each age group. 4.5% of RF patients were treated with oxygen and 2.61% had a lung transplant. With increasing age, 26.6% of RF patients were treated with pancreatic enzymes associated with a more severe lung disease. RF patients had shortened life spans, with mortality starting around the age of 20 years.Patients carrying an RF mutations experience a decline of pulmonary function with age, leading to life-shortening. Standard of care therapies and augmenting CFTR function may improve their survival and quality of life.