Narcolepsy is a sleep disorder which results in sudden and uncontrollable attacks of sleep, and loss of muscular control. It usually begins in adolescence, and is thought to have a biological basis. One explanation of narcolepsy can be attributed to a deficiency in hypocretin, which is involved in regulating arousal levels. Narcolepsy may be due to the body’s immune system attacking the cells that produce hypocretin, which in low levels reduce the ability to sleep. A second explanation of narcolepsy is associated with a genetic abnormality, linked to a mutation in the immune system. The increased frequency of HLA on chromosome 6 is present in narcoleptic sufferers, and thought to affect the sleep-wake cycle (Honda, 1983). The Stanford Medical Centre published research in 2012 which showed that more than 90% of people suffering from narcolepsy have been found to have this HLA variant.
Support for hypocretin deficiency as an explanation of narcolepsy comes from Dement (1999), who found that mice that could not make hypocretin in their brains developed symptoms of narcolepsy (including cataplexy). Similar findings are also present in studies conducted with narcoleptic dogs (which had been specially bred in laboratory conditions for research purposes) whereby those with narcolepsy had a faulty receptor for hypocretin. However, there are issues of extrapolation as findings from animal studies cannot be applied to humans due to the difference in brain structure between species, and the fact that humans are much more complex creatures and cannot be treated the same. There are also ethical concerns due to how the animals were treated during the experiment (i.e: being specially bred just to be experimented on) to find a cure for the disorder. If a treatment was found it cannot be guaranteed to work on humans due to these physiological differences; meaning the treatment of these animals can be considered unjust. Thus, low levels of hypocretin in humans may not contribute to narcolepsy. In animals it appears that narcolepsy is related to a faulty receptor for hypocretin, whereas in humans it seems to be a deficiency in hypocretin.
Further research that challenges the genetic explanation of narcolepsy comes from Dement (99). It was discovered that in humans, if one twin has narcolepsy then there is only a 30% chance of the other twin developing the disorder, meaning that if narcolepsy is present it may be due to another factor in 70% of cases. This means that generally narcolepsy is not inherited, despite the evidence that in dogs it was found that one gene could easily pass on the trait. Furthermore, the HLA variant found in narcoleptics is not found in all individuals with the disorder, and the same HLA variant is common in the general population (Mignot et al, 1997). Therefore, genetics cannot be the only cause of narcolepsy. Both the hypocretin deficiency and genetic explanation can only offer partial accounts of narcolepsy.
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