Pathophysiology of cystic fibrosis: implications for critical care nurses.

Lisa C. Grossman is a first-year medical student at Georgetown University,Washington, DC. in patients who have 10% or more CFTR function. Patients with 1% or less functioning of CFTR generally have a more classic type of cystic fibrosis; however, no definitive correlation exists between the genotype and the phenotype. In patients with 1% or less functioning of the gene, the patients’ cells have very defective CFTR; therefore, chloride, sodium, and water flow is faulty. In about 70% of patients, cystic fibrosis is diagnosed before the patients are 1 year old. Most patients with manifestations of cystic fibrosis have parents who do not have cystic fibrosis but are heterozygotes or carriers of the disease. A heterozygote has 1 dominant allele and 1 recessive allele. If 2 persons who are heterozygous for CFTR have a child, the child can have cystic fibrosis. According to Mendelian inheritance theory, matings between carriers will generate approximately 25% affected offspring (25% chance of having a child with cystic fibrosis) and 75% unaffected offspring (50% chance of having a child who is a carrier and 25% chance of having a child with no cystic fibrosis alleles). If a cystic fibrosis carrier and a homozygote-dominant (no cystic fibrosis alleles) person have a child, the child will not have cystic fibrosis. According to estimates, approximately 7 to 10 million cystic fibrosis carriers exist in the United States who are totally unaware that they carry a mutated CFTR gene. In addition, some persons have 2 mutations of the cystic fibrosis gene and are actually affected with cystic fibrosis and are unaware that they have the disease. A white American couple with no Sheila Grossman, PhD, APRN, BC Lisa C. Grossman, BA, MPH