Introduction
Proper sleep is important for good mental health. The highly prevalent sleep disorders are insomnia, obstructive sleep apnea, and circadian rhythm sleep disorders. The causes of sleep disorders are not exactly known, but genetic factors are considered. Gene is material that carries information from parents to their children. Once it is established that a disorder is heritable, there are several approaches to determine the specific genes or, more generally, chromosomal regions that harbor genetic variants that influence the trait of interest. This task is much more challenging. The way to determine this is to perform a genetic linkage analysis, which relies on the inheritance structure associated with family pedigrees. Genetic linkage summarizes the observation that genes that are closely related to one another on a chromosome (gene-carrying material) are more likely to get passed down to offspring than genes that are further away. At their most basic level, linkage studies involve comparing chromosomal regions between affected and unaffected individuals (i.e. cases and controls) in order to identify those deoxyribonucleic acid (DNA) segments that are more commonly shared between affected relatives, and not between affected and unaffected individuals. This article reviews the genetic basis for sleep disorders and correlates mental health and illness.
What Are Sleep Disorders?
Sleep disorders refer to a group of conditions that affect a person's ability to achieve restful and quality sleep. These disorders can disrupt the sleep patterns and overall sleep-wake cycle, leading to various physical, mental, and emotional consequences. Sleep is an essential physiological process that allows the body to rest, recover, and rejuvenate. Improper sleep can affect a person's overall health and well-being. There are several types of sleep disorders, each characterized by distinct symptoms and underlying causes. Some common sleep disorders include:
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Insomnia: The inability to reliably fall or stay asleep is known as insomnia. Stress is one of the many elements that might contribute to it, along with anxiety, depression, medical conditions, or certain medications. Individuals with insomnia often experience daytime fatigue, irritability, and difficulty concentrating.
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Sleep Apnea: The pauses in breathing while sleeping are a defining feature of sleep apnea. When the airway is entirely or partially closed, it can result in brief periods of breathing cessation. This can result in loud snoring, choking or gasping during sleep, and excessive daytime sleepiness.
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Restless Legs Syndrome (RLS): RLS is a neurological condition that causes irrational urges to move the legs, often accompanied by uncomfortable sensations. Symptoms typically worsen during periods of inactivity or at night, making it difficult to fall or stay asleep.
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Narcolepsy: Narcolepsy is a chronic neurological disorder. It leads to excessive daytime drowsiness, abrupt episodes of sleep, cataplexy (sudden loss of muscle tone), hallucinations, and sleep paralysis.
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Parasomnias: Parasomnias are abnormal behaviors or experiences that occur while slumbering. Sleep talking, sleepwalking, night terrors, and REM (rapid eye movement) sleep behavior disorder (acting out dreams while asleep) are a few examples.
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Circadian Rhythm Disorders: Circadian rhythm disorders involve disruptions in the body's internal clock, affecting the timing of sleep-wake cycles. Examples of circadian rhythm disorders include jet lag, shift work sleep disorder, and delayed sleep phase disorder.
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Restless Sleep Syndrome (Periodic Limb Movement Disorder): Repetitive limb motions are a periodic limb movement disorder symptom. Limb motions during sleep, causing frequent awakenings and disrupted sleep.
What Are the Genetics of Sleeping Disorders?
The two main objectives of research on the genetic basis of sleep disorders are finding genetic variations that increase the risk for disease and how these variations affect the operation of biological systems. Sleep disorders are complex features similar to mental disorders and are believed to be influenced by various gene variations, including deoxyribonucleotides (DNA). DNA is the genetic material that carries information about the parents' traits (characteristics) and carries it to the children. Heritability (the quality of characteristics transmitted to children from their parents) is the percentage of variance for a disease or trait that can be traced to genetic variation in the population. Sleep disorders are heritable means genetic factors play a vital role in causing sleep disorders. The goal of these analyses is to use different types of studies to isolate genetic effects from those of a shared environment. If a sleep disorder, for example, is not heritable then this suggests that genetic factors do not play a strong role in disease cause and there is no need to search for involved genes. In contrast, evidence that a trait is heritable suggests there are underlying variants affecting disease risk.
Genetic factors also affect the normal wake-up and sleep cycle. Heritability allows us to understand the genetic basis for sleep disorders. Heritability is studied using twin or family studies, with the concept that individuals who are more similar genetically should also be more similar phenotypically (by appearance) compared with individuals with less genetic similarity. These analyses aim to use different types of genes in the environment. Candidate genes may be selected in a variety of methods, such as using the findings of earlier genetic research. The biggest limitation of candidate gene studies is that they require making assumptions about which genes are most frequently linked to a trait.
The following are the genetics of different types of sleep disorders:
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Circadian Rhythm Sleep Disorders - Circadian rhythm sleep disorder is a sleep disorder characterized by an earlier circadian phase relative to the desired sleep period. These individuals typically have difficulty staying awake until the desired bedtime and wake up earlier than intended in the morning.
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Genetic of Insomnia - Insomnia is the most prevalent sleep disorder. The heritability of insomnia has been estimated in a series of family and twin studies that relied on self-report measures of insomnia traits.
Conclusion
Sleep disorder genetics is still in its infancy. Inadequate sample sizes and a lack of replication are two study design problems that have plagued many previous research. The most recent genetic discoveries related to narcolepsy and RLS, are partly due to more precise phenotyping techniques and substantial sample numbers. In the case of OSA (obstructive sleep apnea), intermediate qualities connected to the pathophysiology of the condition have also been demonstrated to be heritable may be more important than a diagnosis of sleep apnea. Because the underlying causes of insomnia are unknown, it is more difficult to characterize the illness and identify intermediate phenotypes for genetic research.
