| ||The final breakthrough came in 1989, when the defective gene responsible for CF was isolated. This was heralded as 'one of the most significant discoveries in the history of human genetics'. It led directly to improved diagnosis of the disorder and has improved the genetic counselling offered to affected families.
CF is complicated: not all cases of the disease are caused by the same genetic defect. Some 800 different mutations have been identified in the CF gene, each affecting the proper functioning of CFTR.
The mutations have various effects. In some instances, no CFTR at all is synthesised; in others, it fails the cell's quality control mechanism and becomes stuck in the endoplasmic reticulum, never reaching the membrane. In yet other cases, the protein may be present in the cell membrane, but may not function correctly.