Genetics and environmental factors
Both genetic and environmental factors play an important role in the development of narcolepsy.
The risk of a first-degree relative developing narcolepsy with cataplexy is estimated to be around 1 – 2%, a risk that is 10 – 40 times the higher than in the general population. Studies have shown a relationship between genetic factors to the development of narcolepsy. In particular, the Human Leukocyte Antigen (HLA) gene HLA DQB1*0602 allele is the major genetic susceptibility factor. Possessing this allele is thought to contribute to neural loss and to predispose individuals to this disorder. Approximately 85 – 95% of individuals with narcolepsy with cataplexy are positive for this specific allele, and individuals who are homozygous for this genotype have a two- to four-fold risk of narcolepsy. Interestingly however, the presence or absence of this allele is not linked to ethnic origin.
Although possessing certain genetic factors can predispose an individual to the development of narcolepsy, studies involving narcoleptic identical twins have demonstrated a low rate of concordance. In 2004, Dauvilliers Y, Maret S, Bassetti C, et al. identified monozygotic twins who were homozygous for HLA DQB1*0602 but did not have other features consistent with narcolepsy. Therefore, an individual’s genetic background is not the sole factor behind hypocretin deficiency. It is likely that environmental factors play a role in the development of narcolepsy, acting in combination with genetic factors. The exact nature of such environmental factors remains unknown; some of the postulated factors include head trauma, sudden change in sleep/wake habits, or various infections, which may possibly trigger an autoimmune process with irreversible damage to the hypocretin system.
References
1. Nishino S. Clinical and neurobiological aspects of narcolepsy. Sleep Medicine 2007; 2: 373 – 399
2. Dauvilliers Y., Arnulf I, Mignot E. Narcolepsy with Cataplexy. Lancet (Seminar) 2007; 369: 499 – 511
1. Nishino S. Clinical and neurobiological aspects of narcolepsy. Sleep Medicine 2007; 2: 373 – 399
2. Dauvilliers Y., Arnulf I, Mignot E. Narcolepsy with Cataplexy. Lancet (Seminar) 2007; 369: 499 – 511
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biolinguistics-bcn.blogspot.com
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biolinguistics-bcn.blogspot.com
http://bouldersleeptherapy.com/disorders/narcolepsy.php/
autoimmunediseasesa2z.com
www3.unil.ch