Cystic fibrosis is an autosomal recessive condition caused by a mutation in the CFTR gene that alters Cl- and Na+ transport, leading to excesive mucus accumulation in aerial and digestive tracts.
What is Cystic fibrosis?
Cystic fibrosis is an autosomal recessive condition in which the mutation of a diallelic CFTR gene that codes for the channel CFTR protein (cystic fibrosis transmembrane conductance regulator) is responsible for the affection.
The CFTR protein expresses in the luminal portion of the secretory and absorptive epithelial membranes, and it is involved in Cl- and Na+ transport.
Given that defects in the CFTR protein take to a defective regulation in the Na+ channel, cystic fibrosis characterizes by alterations in electrolytes secretions and absorption. There are two significant physiopathological mechanisms:
1) altered Cl- secretion in submucous glands,
2) increased Na+ absorption and consequent electrolytes hyperabsorption in the superficial epithelium.
Patients with cystic fibrosis are incapable of increasing their secretory transport. On the contrary, the increased epithelial Na+ conductance and the altered permeability to Cl- and water lead to hyperabsorption in the patient epitheliums.
The superficial liquid layer in the aerial vias decreases, mucus is not released from mucous glands, and the mucociliary clearance is strongly altered in aerial vias. Mucus accumulates in the lungs, digestive tract, and other areas.
Most people have two copies of the normal allele (h0m0zyg0us dominant genotype)and produce the functional CFTR protein form.
Patients with cystic fibrosis have two copies of the mutated allele (h0m0zyg0us recessive genotype), producing the protein's mutated and dysfunctional form.
Heter0zyg0us people possess only one normal CFTR allele and a mutated form of the same gene. These alleles are codominant, meaning that noth of them are expressed. They can produce a normal protein and a mutated protein.
Given that the normal allele produces enough functional CFTR protein, these individuals do not have any adverse effects, and the mutated allele is recessive at a physiological level.
To sum up, Cystic fibrosis is an autosomal recessive condition -not sex-linked- that causes the unfunctional form of the CFTR protein, and alters Cl- and Na+ transport. Consequently, there is an accumulation of mucus in the respiratory and digestive tract, among other organs, that might be lethal.
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