Narcolepsy is a rare sleep disorder caused by genetic mutations, particularly in the HLA genes on chromosome six, which trigger autoimmune responses that attack neurons carrying hypocretin. Other genetic causes have also been identified. Environmental factors, such as viral infections and obesity, can also contribute to the disorder.
Narcolepsy is a rare condition in which the biological patterns of sleep and wakefulness are poorly regulated by the brain. Sufferers are prone to excessive daytime sleepiness and quickly fall into a deep sleep in which their muscles may become temporarily paralysed. Despite many years of modern research, the exact causes of narcolepsy remain unclear. The disorder is almost certainly the result of specific genetic mutations, and recent studies have come close to identifying the genes involved and explaining how they trigger symptoms. Additionally, several environmental factors can increase the likelihood of developing the sleep disorder if the underlying genetic causes of narcolepsy are present.
Most sleep experts believe the primary causes of narcolepsy are linked to genetic mutations on chromosome six. A group of genes on the chromosome called the human leukocyte antigen (HLA) complex has been studied extensively. The HLA complex is mainly involved in maintaining the functioning of the immune system in humans. In many people with narcolepsy, mutations in HLA genes appear to trigger autoimmune responses that attack neurons that carry hypocretin, an important chemical that promotes wakefulness. Without enough hypocretin, the brain is unable to maintain normal sleep and wake patterns.
Other genetic causes of narcolepsy have also been identified. In dog studies, researchers found that mutations on chromosome 12 can damage neural receptor sites for hypocretin. Instead of neural cell death, hypocretin deficiency is caused by the inability of neurons to absorb it. Ongoing research hopes to better elucidate the links between hypocretin, narcolepsy, and neural activity.
Genetics alone is usually not enough to trigger narcolepsy. Other factors such as traumatic brain injuries and tumors can impair the parts of the brain that regulate sleep cycles, consciousness and muscle control. In particular, damage to the hypothalamus and pons in the brainstem is closely associated with the expression of narcolepsy symptoms in some patients. Biological factors related to hormonal imbalances and prolonged periods of stress can also contribute to the disorder.
Environmental factors are also potential triggers or causes of narcolepsy for patients genetically predisposed to hypocretin deficiency. Serious viral infections, smoking, exposure to pollutants, and poor dietary choices leading to obesity have all been linked to symptoms of narcolepsy. It is likely that future genetic research and clinical trials will reveal more information about the roles that mutations and environmental factors play in altering brain chemicals and leading to the expression of the disorder.
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