PER2 rs121913533: Understanding Familial Advanced Sleep Phase
The rs121913533 variant is a rare genetic mutation located within the PER2 gene. It is primarily associated with familial advanced sleep phase syndrome (FASPS), a condition characterized by a significantly earlier sleep-wake cycle than is typical for the general population.
What each genotype means
Typical circadian rhythm
This genotype represents the common, non-variant form of the PER2 gene. It is not associated with the specific familial advanced sleep phase syndrome linked to this variant.
This is the most common genotype found in the general population across all ancestries.
Potential advanced sleep phase
This genotype involves one copy of the variant associated with familial advanced sleep phase syndrome (FASPS). Individuals with this variant may experience a significantly earlier sleep-wake cycle, often falling asleep and waking up several hours earlier than the general population. This is an autosomal dominant trait, meaning it can influence sleep timing even with one copy.
This specific variant is extremely rare in the general population and is typically identified only in families with a history of advanced sleep phase syndrome.
Advanced sleep phase syndrome
This genotype involves two copies of the variant associated with familial advanced sleep phase syndrome. Research indicates this mutation alters the phosphorylation site of the PER2 protein, leading to a shortened circadian period and a stable, early sleep-wake schedule. Individuals with this profile typically exhibit a consistent, early sleep onset and offset, often referred to as being a 'morning lark'.
This genotype is exceptionally rare and has been documented primarily in specific families identified through clinical research on circadian rhythm disorders.
What is the rs121913533 Variant?
The rs121913533 variant is a specific change in the DNA sequence of the PER2 gene. In scientific literature, this is often referred to as the S662G mutation, which describes a substitution of the amino acid serine for glycine at position 662 of the PER2 protein. This variant is located in a region of the protein that is critical for its function as a molecular clock component. By altering this specific site, the variant interferes with the normal phosphorylation process—a chemical modification that helps regulate the stability and activity of the PER2 protein. Because this protein is a central gear in the body's internal clock, changes to its structure can disrupt the timing of circadian rhythms, leading to the distinct sleep patterns observed in individuals who carry this specific genetic change.
The Role of the PER2 Gene
The PER2 gene, which stands for Period Circadian Regulator 2, provides instructions for making a protein that is essential for maintaining the body's circadian rhythm. This internal clock governs the 24-hour cycle of physiological processes, including sleep, hormone release, and body temperature. The PER2 protein works in a feedback loop with other clock proteins to oscillate in a rhythmic fashion throughout the day. When the system functions correctly, it allows the body to synchronize its internal state with the external environment, such as the cycle of light and darkness. Disruptions to the PER2 gene can alter the speed or phase of this internal clock. In the case of the S662G mutation, the protein's degradation and transcriptional activity are affected, which effectively 'speeds up' the internal clock, causing the body to signal for sleep and wakefulness several hours earlier than the average person.
Research and Evidence
The association between the rs121913533 variant and familial advanced sleep phase syndrome (FASPS) is supported by clinical research, including studies of families with a history of extreme morningness. Individuals with this variant typically report falling asleep in the early evening and waking up very early in the morning, often without the ability to delay these times. Research using transgenic mouse models has been instrumental in confirming that this specific mutation causes a shorter circadian period, mirroring the human phenotype. While the evidence linking this variant to FASPS is strong within the context of these specific families, it is important to note that sleep timing is a complex trait influenced by many genes and environmental factors. Not everyone with an early sleep schedule carries this variant, and the presence of the variant is considered a rare, high-impact cause of this specific sleep phase disorder.
Understanding Your Information
If you have encountered this variant in a genetic report, it is important to understand that this information is for educational purposes and does not constitute a medical diagnosis. Familial advanced sleep phase syndrome is a rare condition, and sleep patterns are influenced by a wide array of genetic and lifestyle factors. If you are concerned about your sleep quality, timing, or the impact of your sleep schedule on your daily life, you should consult with a healthcare professional or a sleep specialist. They can provide a clinical evaluation, which may include sleep logs or actigraphy, to determine if your sleep patterns are within a normal range or if they warrant further investigation. Never use genetic data to make decisions about your health or to self-diagnose. Always discuss any concerns regarding your sleep health with a qualified clinician who can provide personalized guidance based on your full medical history.
How common is this variant?
The rs121913533 variant is considered rare in the general population. It is primarily identified through clinical studies of families specifically affected by advanced sleep phase syndrome.
Frequently asked questions
What is familial advanced sleep phase syndrome?
It is a rare, inherited condition where a person's internal clock is set several hours earlier than normal. This leads to a consistent pattern of falling asleep in the early evening and waking up very early in the morning.
Is the rs121913533 variant common?
No, this variant is rare. It is not a common polymorphism found in the general population but is instead a specific mutation identified in families with a history of advanced sleep phase.
Can I change my sleep cycle if I have this variant?
Sleep timing is influenced by both genetics and environment. If you have concerns about your sleep, a sleep specialist can discuss behavioral strategies or other interventions that may help manage your sleep-wake schedule.
Does this variant cause other health problems?
While the primary association is with sleep phase, the PER2 gene is involved in many biological processes. Research is ongoing regarding the role of clock genes in broader health, but you should consult a doctor for any specific health concerns.
Sources & further reading
Educational information only, last refreshed 10/10/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Pathogenic missense variant (Ser662Gly) in PER2 that impairs casein kinase phosphorylation, causing familial advanced sleep phase syndrome (FASPS-1).
This intronic variant in the PER2 gene is associated with individual differences in circadian rhythm, sleep timing, and chronotype.
Common missense/synonymous tagging variant in core clock gene PER2 modulating eveningness preference and diurnal phase delay.
An intronic single-nucleotide variant in the core clock gene PER2 recently identified in familial delayed sleep phase syndrome and evening chronotypes.
The classic missense variant (p.Ser663Gly) in PER2 that causes autosomal dominant familial advanced sleep phase syndrome (FASPS1).
Variant in the circadian regulator PER2 associated with circadian rhythm phase, chronotype, and timing of habitual sleep.