The Mutant Cystic Fibrosis Gene on Chromosome 7
Cystic fibrosis (CF) is a hereditary genetic disorder which results in recurrent pulmonary and gastrointestinal symptoms. To understand how an anomalous gene causes this debilitating condition, you have to understand how genes and chromosomes function.
The human Cystic fibrosis transmembrane conductance regulator gene
Each gene is a blueprint for specific proteins, which perform unique functions. The CFTR gene gives instructions to make the cystic fibrosis transmembrane conductance regulator protein which acts as a chloride channel across the membrane of specific cells. The channel regulates the flow of chloride ions in and out of the cell. When chloride leaves the cells, water follows and hydrates the mucus outside the cell, contributing to thin, watery mucus.
In CF, The malfunctioning cystic fibrosis transmembrane conductance regulator protein causes chloride to accumulate in cells. This prevents water from leaving the cells. The mucus around the cells becomes thick and sticky, causing obstruction in the lower parts of the lungs.
In the upper part of the lungs, CFTR regulates the flow of sodium (and water) out of the mucus back into the cells again. In CF this regulation does not exist and thus a lot of water leaves the mucus, making it even more viscous.
The CFTR protein also affects the pancreas by blocking the ducts that secretes enzymes into the duodenum. This blockage initiates cyst formation in glands and the development of respiratory infections.
The fruit of genetic mutation
Any change in the genetic blueprint is termed a mutation. These may result from mistakes made when copies are created, or they may be caused by mutagens like radiation or chemicals. This mutation becomes incorporated into a person’s genetic heritage and can be passed from generation to generation.
Although more than 1400 mutations can cause cystic fibrosis, one in particular accounts for the majority. A deletion at delta F508 on the cystic fibrosis transmembrane conductance regulator gene results in absence of a protein building block called phenylalanine. The resulting regulator protein does not fold properly and is entirely nonfunctional. This causes 70% of all cases worldwide.
The genealogy of this disorder
Chromosomes are like filing cabinets that hold the genetic blueprints. Every single cell in the human body has 23 pairs of chromosomes. You get 23 chromosomes from your mom and 23 from your dad, for a total of 46 chromosome or 23 pairs.
The cystic fibrosis transmembrane conductance regulator gene can be found in a part of chromosome number 7 that is named locus q. Chromosome 7 represents 5% of the total genetic material in human cells, equivalent to 159 million DNA base pairs or bit of information code.
Since each individual has 2 chromosome 7s (one from each parent), every individual has two copies of the genetic blueprint for the cystic fibrosis transmembrane conductance regulator protein.
In order to develop cystic fibrosis, you have to have two defective genes. If no correct set of instructions for the protein exists in your set of chromosomes, your body will be unable to manufacture it.
Disclaimer: This website provides general information about cystic fibrosis and in no means should be taken as a medical or health advice. Please consult your doctor before acting on any of its information.