Northern epilepsy is a genetic condition that causes recurrent seizures (epilepsy) beginning in childhood, usually between ages 5 and 10. Seizures are often the generalized tonic-clonic type, which involve muscle rigidity, convulsions, and loss of consciousness. These seizures typically last less than 5 minutes but can last up to 15 minutes. Some people with Northern epilepsy also experience partial seizures, which do not cause a loss of consciousness. The seizures occur approximately one to two times per month until adolescence; then the frequency decreases to about four to six times per year by early adulthood. By middle age, seizures become even less frequent.
Two to 5 years after the start of seizures, people with Northern epilepsy begin to experience a decline in intellectual function, which can result in mild intellectual disability. Problems with coordination usually begin in young adulthood and lead to clumsiness and difficulty with fine motor activities such as writing, using eating utensils, and fastening buttons. During this time, affected individuals often begin to develop balance problems and they walk slowly with short, wide steps. These intellectual and movement problems worsen over time. A loss of sharp vision (reduced visual acuity) may also occur in early to mid-adulthood.
Individuals with Northern epilepsy often live into late adulthood, but depending on the severity of the intellectual disability and movement impairments, they may require assistance with tasks of everyday living.
Northern epilepsy is one of a group of disorders known as neuronal ceroid lipofuscinoses (NCLs), which are also known as Batten disease. These disorders affect the nervous system and typically cause progressive problems with vision, movement, and thinking ability. The different types of NCLs are distinguished by the age at which signs and symptoms first appear. Northern epilepsy is the mildest form of NCL.
Northern epilepsy appears to affect only individuals of Finnish ancestry, particularly those from the Kainuu region of northern Finland. Approximately 1 in 10,000 individuals in this region have the condition.
Mutations in the CLN8 gene cause Northern epilepsy. The CLN8 gene provides instructions for making a protein whose function is not well understood. The CLN8 protein is thought to play a role in transporting materials in and out of a cell structure called the endoplasmic reticulum. The endoplasmic reticulum is involved in protein production, processing, and transport. Based on the structure of the CLN8 protein, it may also help regulate the levels of fats (lipids) in cells.
A single CLN8 gene mutation has been identified to cause Northern epilepsy. Nearly all affected individuals have this mutation in both copies of the CLN8 gene in each cell. The effects of this mutation on protein function are unclear. Unlike other forms of NCL that result in the accumulation of large amounts of fatty substances called lipopigments in cells, contributing to cell death, Northern epilepsy is associated with very little lipopigment buildup. People with Northern epilepsy do have mild brain abnormalities resulting from cell death, but the cause of this brain cell death is unknown. It is also unclear how changes in the CLN8 protein and a loss of brain cells cause the neurological problems associated with Northern epilepsy.
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
These resources address the diagnosis or management of Northern epilepsy:
These resources from MedlinePlus offer information about the diagnosis and management of various health conditions:
- neuronal ceroid lipofuscinosis 8
- neuronal ceroid lipofuscinosis 8, Northern epilepsy variant
- progressive epilepsy with mental retardation