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

Rational: 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.

Objectives: Characterize disease severity of patients carrying RF mutations, using the European CF Society Patient Registry (ECFSPR) data.

Methods: 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).

Main Results: 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.

Conclusions: 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.