The cell membrane regulates what can enter and leave the cell.
Many substances cannot travel through the membrane, but they can travel through channel proteins. The video below discusses this further.
Cystic fibrosis is an inherited genetic disorder which involves a channel protein. The protein called CFTR normally allows chloride ions (salt) to travel through the membrane. Individuals who have cystic fibrosis have a defective version of CFTR which does not allow chloride ions to move through the membrane. This leads to a loss of homeostasis and results in a build up of mucus in the lungs.
The gene associated with cystic fibrosis was discovered by Francis Collins who later served as director for the Human Genome Project and is now the director of the NIH.
Hope this helps!