The Role of Genetic and Medical-social Factors in the Course of Cystic Fibrosis. Clinical Cases

Cystic fibrosis is a life-shortening, multisystem genetic disease (the most common lethal genetic disease in white population). Cystic fibrosis is a hereditary autosomal recessive disease with lesions of the exocrine glands. Its frequency ranges from 1: 8000 to 1: 2000, and life expectancy is from 10 to 40 years in developed countries. The reason for cystic fibrosis is the numerous mutations in the cystic fibrosis gene, which causes the clinical course of the disease from atypical subclinical forms to severe cystic fibrosis. Since the 1930s, the development and use of an arsenal of symptomatic treatments and extensive prophylactic daily treatment regimens have extended the cystic fibrosis median predicted survival from just a few months following diagnosis to 38 years of age. The discovery of the mutated cystic fibrosis gene (cystic fibrosis transmembrane conductance regulator) in 1989, and the function of wild-type cystic fibrosis transmembrane conductance regulator protein in 1992 established the underlying pathophysiology present in cystic fibrosis epithelial tissues, including that of the sweat gland, the pancreas, the airway, and the intestine. It is now recognized that interventions targeting the underlying cystic fibrosis transmembrane conductance regulator defect across body systems have the potential to improve outcomes throughout life for persons with cystic fibrosis. The reason for cystic fibrosis is the numerous mutations in the cystic fibrosis gene, which causes the clinical course of the disease from atypical subclinical forms to severe cystic fibrosis. Results and discussion. More than 2000 mutations and 200 polymorphisms in the cystic fibrosis gene were described; its mutations were divided into 6 classes. Class I mutations result in no functional cystic fibrosis transmembrane conductance regulator protein being produced because of absent or defective protein biosynthesis. Class II mutations result in protein variants, which are improperly processed or transported to the apical cell membrane. For example, the most common and best characterized cystic fibrosis transmembrane conductance regulator mutation, F508del, is a class II mutation. One copy of F508del is present in 70% of the affected population, and 2 copies are present in approximately 50%. Class III mutations affect cystic fibrosis transmembrane conductance regulator activation and hinder chloride movement through channels at the cell surface. For example, G551D is a class III gating mutation targeted by the medication invocator, which improves chloride conductance in individuals with Cystic fibrosis with at least one copy of this mutation. Class IV mutations result in defects that produce a normal or diminished amount of cystic fibrosis transmembrane conductance regulator with decreased function at the apical epithelial cell membrane. Class V mutations result from decreased amounts of fully active cystic fibrosis transmembrane conductance regulator. Class VI mutation is characterized by diminished stability of a fully processed and functional cystic fibrosis transmembrane conductance regulator at the cell surface and often results in the truncation of cystic fibrosis transmembrane conductance regulator toward the carboxyl terminus. The disease results from 2 cystic fibrosis transmembrane conductance regulator mutations. However, they need not be from the same class. The amount of functional cystic fibrosis transmembrane conductance regulator present at the cell surface, which is determined by genotype, partially accounts for the wide spectrum of cystic fibrosis phenotypes and, to some extent, correlates with the degree of organ involvement and disease severity. Class I, II, and III mutations are typically associated with early involvement of respiratory and digestive manifestations (chronic cough, recurrent sinopulmonary infections, and exocrine pancreatic insufficiency).