AANAT rs28936679: Genetics of Melatonin and Sleep Phase
rs28936679 is a rare missense variant in the AANAT gene, which encodes the rate-limiting enzyme in pineal melatonin synthesis. The variant alters an amino acid in the enzyme (p.Ala129Thr) and has been evaluated for its potential role in shifting circadian rhythms and increasing susceptibility to delayed sleep phase syndrome. In public genomic databases like ClinVar, it is classified as a variant of uncertain significance with moderate biological plausibility.
What each genotype means
Typical melatonin synthesis
This is the most common genotype observed in the general population. It is considered the reference sequence and is not associated with the specific sleep-related changes linked to the A variant.
This is the most common genotype globally.
Potential sleep phase variation
This genotype has been reported in research as a potential susceptibility factor for delayed sleep phase disorder, a condition where an individual's internal clock is shifted later than typical. Because this variant is rare, its clinical significance remains an area of ongoing study, and it should not be used to diagnose sleep disorders.
This genotype is rare, with the A allele occurring at a frequency of less than 1% in most continental populations.
Rare variant carrier
This genotype represents the homozygous state for the rare variant. While the A allele has been linked to susceptibility for delayed sleep phase syndrome in specific research cohorts, the rarity of this genotype means that its full impact on individual sleep patterns is not yet fully understood.
This genotype is extremely rare in the general population.
What Is rs28936679 and Where Is It Located?
rs28936679 is a single nucleotide polymorphism located in the coding sequence of the AANAT gene on human chromosome 17. At the DNA level, it typically involves a G-to-A transition on the forward genomic strand. This nucleotide change results in a missense substitution in the encoded polypeptide chain, replacing an alanine with a threonine at amino acid position 129 (p.Ala129Thr). Because it alters the primary protein sequence within an functionally conserved region of the enzyme, it has drawn interest from researchers mapping the genetic architecture of sleep architecture and human chronotypes. In public genetic registries, including NCBI dbSNP and ClinVar, the variant is tracked under accession records evaluating inherited traits related to the sleep-wake cycle.
The Biological Role of the AANAT Enzyme
The AANAT gene encodes arylalkylamine N-acetyltransferase, widely known as the molecular 'timezyme' of the vertebrate circadian apparatus. Expressed prominently in the pineal gland and the retina, AANAT controls the penultimate and primary rate-limiting step in melatonin biosynthesis: transferring an acetyl group from acetyl-CoA to serotonin, forming N-acetylserotonin. Pineal AANAT activity oscillates dramatically between day and night, climbing by orders of magnitude in darkness under the direction of the brain's master pacemaker, the suprachiasmatic nucleus. Phosphorylation allows the enzyme to bind protective 14-3-3 scaffold proteins, shielding it from rapid proteasomal degradation during the night. Because of its pivotal role in regulating nocturnal melatonin surges, changes to the structural stability or catalytic kinetics of AANAT can theoretically shift the timing of sleep-wake rhythms.
Scientific Evidence and Link to Delayed Sleep Phase
Delayed Sleep Phase Disorder (DSPD) is a circadian rhythm disorder where an individual's natural sleep onset and wake times are persistently delayed by several hours compared to conventional social norms. Biochemical characterizations of the p.Ala129Thr substitution have suggested that the amino acid replacement alters enzyme kinetics and sensitivity to temperature or regulatory binding, potentially flattening or delaying peak melatonin output. Clinical and candidate-gene studies initially reported this variant in individuals presenting with delayed sleep phase tendencies. However, large-scale modern association studies demonstrate that delayed sleep phase syndrome is polygenic, influenced by multiple clock-gene mechanisms including CRY1, PER2, and PER3. Consequently, ClinVar classifies rs28936679 as a variant of uncertain significance (VUS), reflecting moderate laboratory plausibility but insufficient population-level statistical proof to declare it definitively causal.
Population Frequency and Ancestry Patterns
rs28936679 is an exceedingly rare allele across the global human population. Population reference aggregations, such as the Genome Aggregation Database (gnomAD), indicate that the minor allele frequency (MAF) is substantially less than 1% (<0.01) across almost all continental groups. The vast majority of individuals carry the ancestral homozygous reference genotype (GG), which produces the standard alanine-containing enzyme. Heterozygous carriers (GA) are infrequently encountered, and homozygous alternative individuals (AA) are exceptionally scarce in population sequencing cohorts. Because statistical power is limited when evaluating rare variants, broader multi-ancestry biobank analyses are still underway to establish whether the variant exhibits higher penetrance or distinct allele distribution patterns in specific isolated cohorts.
Interpreting Your Result: What You Can and Cannot Do
Discovering an altered allele at rs28936679 does not constitute a clinical diagnosis of delayed sleep phase disorder, nor does having the typical genotype guarantee standard sleep timing. Circadian alignment is governed by a combination of polygenic background, ocular light exposure, daily habits, and environmental entrainment. This genetic information is educational and describes biological predisposition rather than destiny. Individuals experiencing intractable difficulty falling asleep at conventional times, chronic morning grogginess, or daytime fatigue should consult a sleep medicine specialist or primary physician for formal evaluation. Readers using exogenous melatonin, light therapy, or circadian-modulating medications should never adjust timing or dosages based on personal genomic data without professional clinical guidance.
How common is this variant?
rs28936679 is globally rare, with a minor allele frequency well below 0.01 across major continental populations in large sequencing databases like gnomAD.
Frequently asked questions
Does having the rs28936679 variant mean I definitely have delayed sleep phase syndrome?
No, carrying the variant does not mean you will develop delayed sleep phase syndrome. It is a rare genetic marker categorized as a variant of uncertain significance, meaning it reflects biological susceptibility rather than a deterministic diagnosis. Environmental factors such as evening screen exposure and daytime light cycles play a profound role in sleep timing.
How does AANAT influence when I feel tired?
AANAT acts as the enzymatic pacemaker for melatonin production in the pineal gland. When light fades, AANAT enzyme levels rise sharply, catalyzing the production of melatonin that signals night to the body. Variations that alter the enzyme's function can change the amplitude or timing of that nocturnal melatonin surge.
Can taking over-the-counter melatonin overcome this genetic variant?
While exogenous melatonin supplements can help shift circadian rhythms under appropriate clinical guidance, you should not self-medicate based on a genotype. The timing and dose of melatonin are crucial to effectively adjusting circadian phase without disrupting daytime alertness, so consulting a physician or sleep specialist is advised.
Is rs28936679 the primary gene variant linked to being a night owl?
No, being an evening chronotype or having a delayed sleep schedule is influenced by dozens of genes across core circadian loops, including CRY1, PER2, and CLOCK, alongside lifestyle cues. rs28936679 in AANAT is one of several candidate markers studied specifically for its direct link to the melatonin manufacturing pathway.
Sources & further reading
Educational information only, last refreshed 9/6/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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