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Somnambulism, or sleepwalking, is a common disorder affecting about a quarter of adolescent humans and about 3% of adult humans (Hublin 1997). Somnambulism is initiated during slow wave sleep, can occur as frequently as nightly (Lecendreux 2011), vary from benign to dangerous and even homicidal behavior, and has an increased comorbidity with anxiety and personality disorders (Kales 1987, Gau & Soong 1999). While somnambulism may differ across cultures "clear evidence regarding culturally related differences in the presentation of these disorders is lacking" (Paniagua 2000).
Several independent studies have suggested that somnambulism has a strong inheritable component, including in one family an apparent autosomal dominant inheritance with reduced penetrance (Licis 2011) perhaps due to mutation in noncoding regulatory regions to the adenosine deaminase gene ADA, as adenosine inhibition increases slow wave sleep activity. Another study found that somnambulists are significantly more likely to be reactive to a specific HLA-DBQ subtype antigen, the family of which have been associated with REM disorders (Lecendreux 2011).
The possible selective process for somnambulism is unknown. Somnambulism is associated with longer bouts of slow wave sleep; the behavior may be a side effect of the unique human sleep cycle in which the relatively long SWS period exacerbates individual variability in SWS patterns to the point of unconscious waking. Chimpanzee’s have a slight shorter average sleep cycle (90min) compared to humans (95.8) but relative long total sleeping period (9.7 and 8 hours, respecitively), and to date no non-human primates have been reported to show behavior reminiscent of somnambulism (Kantha 2004). While dogs have been suggested to sleep walk, but the behavior does not clear the distinction between “automatism” (eg, twitching, lunging, jerking) and the highly coordinated behavior seen in humans.
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