The CTSF gene provides instructions for making an enzyme called cathepsin F. Cathepsin F is one of a family of cathepsin proteins that act as proteases, which modify proteins by cutting them apart. Cathepsin F is found in many types of cells and is active in lysosomes, which are compartments within cells that digest and recycle different types of molecules. By cutting proteins apart, cathepsin F can break proteins down, turn on (activate) proteins, and regulate self-destruction of the cell (apoptosis).
At least five mutations in the CTSF gene have been found to cause Kufs disease type B. This condition is a type of neuronal ceroid lipofuscinosis (NCL) characterized by progressive problems with movement and a decline in intellectual function beginning in adulthood. Most of the CTSF gene mutations that cause Kufs disease type B change single protein building blocks (amino acids), resulting in a cathepsin F protein with reduced function. This decrease in cathepsin F function likely slows the normal breakdown of proteins and other materials. In the lysosomes of nerve cells (neurons) in the brain, these materials accumulate into fatty substances called lipopigments. These accumulations can result in cell dysfunction and eventually cause cell death. The progressive death of neurons contributes to the movement problems and intellectual decline characteristic of Kufs disease.