BHLHE41 rs121912618: What Your Genotype Means
The rs121912618 variant is a rare genetic change located in the BHLHE41 gene. It has been associated with a phenotype characterized by reduced nightly sleep duration and increased resilience to the cognitive effects of sleep deprivation.
What each genotype means
Typical sleep duration profile
This is the most common genotype found in the general population. Individuals with this genotype generally follow standard sleep regulation patterns and do not possess the specific genetic factor associated with the short sleeper trait or enhanced resistance to sleep deprivation linked to this variant.
Carried by the vast majority of the human population; the alternative C allele is rare.
Potential short sleep trait
This genotype includes one copy of the variant, also referred to as p.Tyr362His. Research suggests that carriers of this variant may experience reduced nightly sleep duration and show increased resistance to the neurobehavioral effects of sleep deprivation, such as fewer performance lapses, compared to non-carriers.
This is a rare genotype, identified in only a very small percentage of individuals in studied cohorts.
Potential short sleep trait
This rare genotype involves two copies of the variant, p.Tyr362His. Studies on BHLHE41 variants indicate that this mutation reduces the protein's ability to inhibit specific circadian clock-driving transcription factors, which is associated with a shorter habitual sleep duration and improved resilience during periods of sleep loss.
This genotype is extremely rare in the general population.
Understanding the Variant
The variant rs121912618, often referred to in scientific literature by its protein-level change Y362H (tyrosine to histidine at position 362), is a specific alteration within the BHLHE41 gene. This gene, also known as DEC2, encodes a protein that acts as a transcriptional repressor. In the context of human genetics, this variant is considered rare. It sits within a region of the gene that is critical for its function in regulating circadian rhythms. When researchers identify such variants, they look at how the change in the DNA sequence might alter the resulting protein's ability to interact with other molecular components in the body. Because this variant is rare, it is not typically found in standard population screening panels, and its presence is usually identified through specialized research studies focusing on sleep behavior and circadian biology.
The Role of the BHLHE41 Gene
The BHLHE41 gene plays a fundamental role in the regulation of the human circadian clock. The protein it produces functions by competing with other proteins, such as CLOCK and BMAL1, for binding sites on DNA known as E-boxes. By doing so, it effectively represses the expression of certain genes that are essential for maintaining the timing and duration of sleep. Research suggests that the BHLHE41 protein is a key component in the molecular machinery that helps the body determine how much sleep is necessary for recovery. When the function of this gene is altered, it can disrupt the normal feedback loops that govern sleep-wake cycles. This makes BHLHE41 a primary target for scientists studying familial natural short sleep and other conditions where individuals exhibit non-traditional sleep patterns or unusual responses to sleep loss.
Research and Evidence
Evidence linking rs121912618 to sleep traits is considered moderate and is primarily derived from small, well-phenotyped cohorts, including twin studies. In one notable study, a carrier of the Y362H variant was observed to sleep significantly less than their non-carrier twin while simultaneously showing fewer performance lapses during periods of extended sleep deprivation. Laboratory experiments have shown that this specific variant reduces the protein's ability to suppress the activity of the CLOCK/BMAL1 complex, providing a potential molecular mechanism for the observed sleep traits. While these findings are compelling, they are based on limited sample sizes. It is important to note that while this variant is associated with these traits in specific research contexts, it does not account for the vast majority of sleep duration variability in the general population, which is highly polygenic and influenced by many different genetic and environmental factors.
Population Frequency
The rs121912618 variant is classified as rare in human populations. Because of its low frequency, it is not commonly encountered in large-scale genomic databases, and its prevalence across different ancestral groups remains largely uncharacterized. Most data regarding this variant come from targeted studies of individuals with specific sleep phenotypes rather than broad population surveys.
Interpreting Your Information
If you have information regarding your status for this variant, it is important to understand that this is a research-level finding. This information should not be used to diagnose sleep disorders or to make medical decisions. Sleep duration is a complex trait influenced by a wide array of genetic, lifestyle, and environmental factors. If you are concerned about your sleep patterns, the quality of your rest, or your ability to function during the day, you should consult with a qualified healthcare provider or a sleep specialist. They can provide a comprehensive evaluation that considers your overall health history, rather than focusing on a single genetic variant. Never attempt to alter your sleep habits or use medications based on genetic test results without first discussing the implications and potential risks with your clinician or pharmacist.
How common is this variant?
The rs121912618 variant is rare, and its frequency is not well-established across diverse global populations.
Frequently asked questions
Does having this variant mean I have a sleep disorder?
No. This variant is associated with a natural short sleep phenotype in research studies, not a clinical sleep disorder. It describes a biological variation in sleep needs rather than a medical condition.
Can I use this variant to predict how much sleep I need?
Genetic variants are only one small part of the complex factors that determine sleep needs. You should rely on how you feel and your daily functioning to determine your sleep requirements, not genetic test results.
Is this variant the same as the DEC2 mutation?
Yes. BHLHE41 is the official gene name, and DEC2 is a common alias for the same gene. The variant rs121912618 is a specific mutation within this gene.
Should I get tested for this variant?
There is no clinical utility in testing for this rare variant. It is primarily of interest in academic research and does not provide actionable medical information for the general public.
Sources & further reading
Educational information only, last refreshed 9/15/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs121912618?
Upload a raw DNA file from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA and see this variant — plus thousands more — interpreted in your full report.
Get my report — $29Related variants in BHLHE41
Rare missense variant (p.Pro384Arg) in BHLHE41 (DEC2) associated with the 'short sleep' phenotype, characterized by reduced sleep need and resistance to sleep deprivation.
This missense variant (p.Pro384Arg) is associated with familial natural short sleep (FNSS1), an autosomal dominant trait characterized by a reduced need for sleep.
The P384L missense variant in BHLHE41 (DEC2) reduces core circadian repressor function and leads to a natural short sleep duration phenotype.
Rare missense variant (Tyr362His) in BHLHE41; associated with short sleep duration and resistance to sleep deprivation.
A missense mutation (p.Pro385Arg) in BHLHE41 (DEC2) that confers a natural short sleep phenotype.
Coding variant (p.Tyr362His) in BHLHE41 (DEC2) associated with familial natural short sleep phenotype and increased resilience to sleep deprivation.