ceroid-lipofuscinosis, neuronal 6, late infantile, variant
The CLN6 gene provides instructions for making a protein whose function is not well understood. The CLN6 protein is found within a cell structure called the endoplasmic reticulum, which is involved in protein processing and transport. Research suggests that the CLN6 protein regulates the transportation of certain proteins and fats from the endoplasmic reticulum to lysosomes. Based on this function, the CLN6 protein appears to help in the process of ridding cells of materials they no longer need.
Mutations in the CLN6 gene are the most common cause of Kufs disease type A. This condition is a type of neuronal ceroid lipofuscinosis (NCL) characterized by seizures, progressive problems with movement, and a decline in intellectual function beginning in adulthood. Most of the CLN6 gene mutations that cause Kufs disease type A change single protein building blocks (amino acids), resulting in a CLN6 protein with reduced function.
In Kufs disease, fatty substances called lipopigments accumulate in the lysosomes of nerve cells (neurons) in the brain. These accumulations can result in cell dysfunction and eventually cause cell death. The progressive death of neurons contributes to the signs and symptoms of Kufs disease. However, it is unclear how mutations in the CLN6 gene are involved in the buildup of lipopigments and the features of Kufs disease. Research suggests that CLN6 gene mutations that cause Kufs disease allow enough functional protein to be produced so that signs and symptoms of the disorder do not develop until adulthood. The presence of other proteins that compensate for the lack of CLN6 protein could also play a role in the appearance of symptoms in adulthood.
More than 60 mutations in the CLN6 gene have been found to cause late-infantile NCL. This condition impairs motor and mental development beginning in early childhood, causing movement disorders and a decline in intellectual function. In addition, affected children often develop recurrent seizures (epilepsy) and vision impairment. Certain CLN6 gene mutations have been found to cause most cases of late-infantile NCL in Costa Rica, Portugal, and the Canadian island of Newfoundland. Most CLN6 gene mutations result in the production of abnormal CLN6 proteins that are quickly broken down. This rapid degradation of CLN6 protein results in a severe reduction of functional protein and contributes to the childhood appearance of symptoms in people with late-infantile NCL.
Lipopigments accumulate in the lysosomes of people with late-infantile NCL. Unlike in Kufs disease (described above), these accumulations occur in cells throughout the body and can result in cell dysfunction and eventually cause cell death. Neurons are particularly vulnerable to damage caused by lipopigments and more susceptible to cell death. The progressive death of neurons contributes to the signs and symptoms of late-infantile NCL. However, it is unclear how mutations in the CLN6 gene are involved in the buildup of lipopigments and the signs and symptoms of late-infantile NCL.
- ceroid-lipofuscinosis neuronal protein 6