What are the genetic changes related to late-infantile neuronal ceroid lipofuscinosis ?
Mutations in the TPP1 gene cause most cases of late-infantile NCL. Mutations in the CLN5, CLN6, CLN8, MFSD8, and PPT1 genes each account for a small percentage of cases.  The TPP1 gene produces an enzyme called tripeptidyl peptidase 1. This enzyme is found in cell structures called lysosomes, which digest and recycle different types of molecules. Tripeptidyl peptidase 1 breaks down protein fragments, known as peptides, into their individual building blocks (amino acids).  The proteins produced from the other genes involved in this condition are active either in lysosomes or in another cell compartment called the endoplasmic reticulum. The endoplasmic reticulum is involved in protein production, processing, and transport. Within these cell structures, the proteins largely play roles in the breakdown of other proteins or substances.  Mutations in the TPP1, CLN5, CLN6, CLN8, MFSD8, or PPT1 gene usually reduce the production or activity of the particular protein or enzyme made from the gene. In many cases, a reduction in functional protein or enzyme results in incomplete breakdown of certain proteins and other materials. These materials accumulate in the lysosome forming fatty substances called lipopigments. In some cases, it is unclear what causes the buildup of lipopigments. In late-infantile NCL, these accumulations occur in cells throughout the body, but neurons seem particularly vulnerable to damage caused by lipopigments and a decrease in specific protein function. The progressive death of cells in the brain and other tissues leads to the signs and symptoms of late-infantile NCL.