CLN3 Disease

Juvenile

What is the cause?
The gene called CLN3 lies on chromosome 16 and was discovered in 1995. CLN3 disease is inherited as an autosomal recessive disorder, which means that both chromosomes carry mutations in the CLN3 gene, and both parents are unaffected carriers. This gene codes for a transmembrane protein. The nerve cells cannot function as they should and symptoms develop.

How is it diagnosed?
The diagnosis is usually made by genetic (CLN3) tests on blood samples. Occasionally a skin biopsy may be necessary.

Does it have any alternative name?
At the beginning of the 20th century Dr. Frederick Batten described a group of disorders that now bear his name. Over time it was discovered that there were several types of the disease with similar but distinct features and ages at onset of symptoms: infantile, late infantile, juvenile, and adult. CLN3 disease is often called Batten disease, or Spielmeyer- Sjogren-Vogt disease.

How does the disease progress?
Children are healthy and develop normally for the first few years of life. The first sign of the disease is usually a gradual loss of vision between 4 and 7 years of age. This may be noticed first at nursery or at school. Vision changes rapidly over 6 to 12 months initially but children retain some awareness of color and light/dark until later. By the end of primary school, children are beginning to show some difficulties with concentration, short-term memory and learning. Many are still able to attend mainstream school but may need extra learning support in the classroom. The next stage of the disease starts with the onset of epileptic seizures (average age of onset of seizures is 10 years). Often the first seizures are motor seizures with violent jerking of the limbs and loss of consciousness. Seizures may be controlled by medicines for several months or years, but always recur, eventually becoming difficult to control completely. The pattern of seizures may change over time and other seizure types may evolve, such as vacant spells and episodes of partial awareness with fiddling and muddled speech.

During the teenage years children tend to slowly become more unsteady on their feet. At around the same time speech may become repetitive and gradually more difficult to understand. Not uncommonly children become anxious and tend to worry. Some feel things, hear voices or see things that are unreal. Teenagers become less able and increasingly dependent. The course of the disease is extremely variable even for children from the same family. The teenagers and young adults are much more able some days than others, especially in terms of mobility, communication and feeding skills. The disease progresses with periods of stability which may last months or years alternating with periods of deterioration lasting several months which may be triggered by intercurrent illness. Death usually occurs between the ages of 15 and 35 years (but occasionally later).

 

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