The Familial Connection in Sleep Disorders


One of the biggest mysteries concerning human body functions is our biological requirement of sleep. Most adults are recommended to get around 7 to 9 hours of sleep, while adolescents and children are expected to get a range from 7 to 14 hours of sleep a day on average (National Sleep Foundation, 2015). Unfortunately for many, the parameters of these recommendations are not met and may be attributed to sleep disorders. With about 70 million Americans having some form of sleep disorder, the prevalence of sleep disorders has been on a steady increase. Despite its relative prevalence, and the subsequent increase in prevalence, sleep disorders are widely misunderstood and are often mistaken as a symptom of another mental disorder rather than a disorder on its own. Part of the mystery and misunderstandings of sleep disorders stems from the potential causes of the development of sleep disorders. While in the case of some sleep disorders (like sleep apnea) medication or physiological aspects of the person may be the causal factors, recent research has found genetic implications in sleep disorder causes. 

For some sleep disorders, the direct cause of development is linked to a heritable gene mutation. Fatal familial insomnia is a rare sleep disorder where the inability to sleep progressively increases and leads to mental deterioration (with symptoms that include hallucinations, rapid weight loss, and uncoordinated movement known as ataxia) until death (Genetic and Rare Disease Information Center, n.d.). The disorder is caused by a variant in the PRNP gene that is responsible for the creation of the prion protein, a protein with unspecified and relatively unknown functions in the brain. What is known, however, is that the variant in the PRNP gene results in an abnormal protein shape that builds up in the brain in the form of a toxin called prion (National Organization for Rare Disorders, 2018). This build-up leads to neuron loss and damage that contributes to the symptoms of the disorder and eventually death. While the mutation in the gene can be spontaneous, it can be passed to children genetically in the “autosomal dominant form” (National Organization for Rare Disorders, 2018). 

Similarly, in certain sleep disorders related to the human circadian rhythm, circadian rhythm disorders, an autosomal dominant inherited mutation, are the direct cause of the disorder development. Circadian rhythm disorders are characterized by their impact on the timing of sleep (Cleveland Clinic, n.d.). Those with a circadian rhythm disorder may experience difficulty falling asleep, staying asleep, and issues with waking up too early. circadian rhythm disorders are found to be directly linked with “polymorphism in hPER2 alkylamine, ran-acetyltransferase and HLA genes” (Bidaki et al., 2012). Specifically, in the case of the autosomal dominant form of familial advanced sleep phase syndrome (a disorder where individuals experience continued disruption by undesired early wakings), mutations in the human period 2 gene (hPER2) have been found to be an associated contributing factor (Bidaki et al., 2012). 

For many other sleep disorders, while there hasn’t been an explicit gene that has been found to directly cause their development, there are frequencies within families that have led to the suggestion and association of genes increasing the probability of manifestation. Families with a history of restless leg syndrome have a 3-6 times higher risk in close relatives. In sleepwalking, the risk of a child sleepwalking is 45% more likely to develop if one or both parents are (or have been) sleepwalkers, in comparison to the 22% risk if the parents are not (Bidaki et al., 2012). In the case of narcolepsy, individuals with close relatives that have the disorder have a 1-2% probability of also having narcolepsy, which is 10-40 times higher than the probability of the general population (Bidaki et al., 2012). Another example of the association between family and sleep disorders is displayed in one study conducted on people with common insomnia. Among the participants with common insomnia, it was found that 72.7% of primary insomniacs had a familial tendency and 43.3% of psychiatric insomniacs were also found to have a familial tendency (Liu, 2019). Other indirect familial associations can be made for sleep disorders like obstructive sleep apnea. Individuals with obstructive sleep apnea experience physiological airway blockage during sleep that stops breathing. A primary risk factor in obstructive sleep apnea is obesity, and though FTO (obesity associated gene) may not be the deciding factor in an individual developing obesity, the risk of obesity is 50% if one parent is obese and 80% if both parents are obese (Univeristy of San Fransisco- Benioff Childrens Hospital, n.d.), thus increasing the risk of obstructive sleep apnea. 

While researchers and doctors alike are still trying to unravel the mystery of sleep and sleep disorders, it remains clear that genetics and family history have influence on the development of sleep disorders to some extent. Though the degree of extent varies, as does the mode of impact and influence in the onset of sleep disorders in people, important discoveries on genetic influences have and are currently still being made. It should be noted, however, that correlations may not necessarily equate to causation, but the associations and the relationship between risk factors should still be considered in addressing sleep disorders. As we continue to further understand and grasp the nature of sleep disorders, more accurate diagnosis and general knowledge will be made available to the public, inching us closer to a community of open and inclusive information and treatment for all. 

 

References

 Bidaki, R., Zarei, M., Khorram Toosi, A., & Hakim Shooshtari, M. (2012). A review on genetics of sleep disorders. Iranian journal of psychiatry and behavioral sciences, 6(1), 12-19. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3939950/ 

Circadian Rhythm Sleep Disorders (n.d.). Cleveland Clinic. Retrieved November 22,  2020, From https://my.clevelandclinic.org/health/diseases/12115-circadian-rhythm-disorders 

Fatal Familial Insomnia (n.d.). Genetic and Rare Disease Information Center. Retrieved November 22 2020, from 

https://rarediseases.info.nih.gov/diseases/6429/fatal-familial-insomnia 

Fatal Familial Insomnia (2018). National Organization for Rare Disorders. https://rarediseases.org/rare-diseases/fatal-familial-insomnia/ 

Liu, Wenjing. (2019, January 10). Mini-review: Genetics of common types of sleep disorders. AIP Conference Proceedings. https://doi.org/10.1063/1.5085528 

Obesity (n.d.). University of San Francisco- Benioff Children’s Hospital National Organization for Rare Disorders. Retrieved November 22,  2020 from https://www.ucsfbenioffchildrens.org/conditions/obesity/ 

PRNP Gene. (n.d.). Medline Plus. Retrieved November 22 2020, from https://medlineplus.gov/genetics/gene/prnp

National Sleep Foundation Recommends New Sleep Times. (2015, February 2). National Sleep Foundation. 

https://www.sleepfoundation.org/press-release/national-sleep-foundation-recommends-new-sleep-times 

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