DNAJC5 gene

At least two mutations in the DNAJC5 gene have been found to cause CLN4 disease. CLN4 disease is an inherited disorder that primarily affects the nervous system. This condition usually begins in adulthood with problems with movement and intellectual function that worsen over time.

One of the DNAJC5 gene mutations replaces the protein building block (amino acid) leucine with the amino acid arginine at position 115 in the CSPα protein (written as L115R). The other mutation deletes the amino acid leucine at position 116 in the protein (written as L116del). Affected individuals have one of these mutations in one copy of the DNAJC5 gene in each cell, which leads to the production of an altered protein that cannot associate with the membrane of synaptic vesicles. The resulting reduction in protein recycling leads to a shortage (deficiency) of functional proteins, which impairs the efficiency of nerve impulse transmission. The abnormal CSPα protein may also bind to the functional CSPα protein that is produced from the normal copy of the DNAJC5 gene and prevent it from associating with synaptic vesicles, further impairing impulse transmission. Without communication between nerve cells, neurological functions are impaired, contributing to the features of CLN4 disease.

CLN4 disease is characterized by the accumulation of proteins and other substances in lysosomes, which are compartments in the cell that digest and recycle materials. These accumulations occur in cells throughout the body; however, nerve cells seem to be particularly vulnerable to their effects. The accumulations can cause cell damage leading to cell death. The progressive death of nerve cells in the brain and other tissues contributes to the decline of neurological function in CLN4 disease. However, it is unclear how mutations in the DNAJC5 gene are involved in the buildup of substances in lysosomes.