CRY1 rs184039278: Genetics of Delayed Sleep Phase
The genetic variant rs184039278 is an intronic single nucleotide polymorphism in the core circadian regulator gene CRY1. It disrupts a critical splice site, leading to exon skipping and creating a hyperactive clock repressor protein. Inheritance of this variant is strongly associated with familial delayed sleep phase disorder (DSPD), leading to pronounced delays in daily sleep timing and altered circadian rhythms.
What each genotype means
Typical circadian rhythm
This is the common, wild-type genotype for this position in the CRY1 gene. It is not associated with the gain-of-function splice variant linked to delayed sleep phase disorder.
This is the most common genotype found in the general population across all ancestries.
Increased delayed sleep risk
This genotype includes one copy of the gain-of-function variant, which acts in a dominant manner to lengthen the internal circadian period. Carriers may experience a tendency toward delayed sleep phase disorder, characterized by a preference for staying up late and difficulty falling asleep at conventional times.
This variant is rare, with a minor allele frequency typically reported between 0.3% and 0.6% in non-Finnish European populations.
Increased delayed sleep risk
This genotype includes two copies of the gain-of-function variant. Research indicates that this variant functions dominantly to enhance transcriptional repression, and studies have observed no significant phenotypic differences between individuals with one or two copies of the variant.
This homozygous genotype is very rare in the general population.
Molecular Anatomy of rs184039278
The single nucleotide variant rs184039278 represents an adenine-to-cytosine transversion (c.1657+3A>C) located at the 5' splice donor site directly following exon 11 of the CRY1 gene on chromosome 12q23. In genomic transcripts, nucleotide positions immediately flanking exon-intron boundaries are highly conserved to direct accurate pre-mRNA processing. The substitution of a cytosine at the +3 position disrupts normal spliceosome recognition, provoking the complete omission of exon 11 during pre-mRNA splicing. Because exon 11 spans 72 nucleotides, its loss preserves the reading frame while eliminating exactly 24 amino acids from the C-terminal region of the encoded protein. This truncated product, designated CRY1Δ11, lacks an auto-inhibitory regulatory segment, altering its biophysical properties without causing full protein degradation.
Biological Role of the CRY1 Molecular Clock
The CRY1 gene encodes Cryptochrome Circadian Regulator 1, an essential feedback component of the cell-autonomous mammalian circadian clock. Under standard physiology, circadian timing relies on a negative transcriptional feedback loop. The transcription factor heterodimer formed by CLOCK and BMAL1 binds genomic enhancer elements to promote the transcription of diverse target genes, including CRY1 and period genes. As CRY1 protein accumulates in the cytoplasm, it dimerizes, translocates to the nucleus, and directly interacts with the CLOCK-BMAL1 complex to shut down transcription. In the case of the CRY1Δ11 isoform generated by rs184039278, removal of the auto-inhibitory domain confers a gain-of-function effect: it exhibits heightened affinity for CLOCK-BMAL1 and exerts abnormally potent, prolonged transcriptional repression. This extended inhibitory phase slows down the cellular clock cycle, stretching the intrinsic biological day beyond normal parameters.
Clinical Associations and Strength of Evidence
Genetic evidence linking rs184039278 to delayed sleep–wake timing is robust and supported by both molecular and clinical pedigree analyses. Groundbreaking work published in Cell identified the variant in families affected by autosomal dominant delayed sleep phase disorder (DSPD). Cellular models from carriers exhibited lengthened circadian periods, providing a mechanistic explanation for their delayed sleep cycles. Subsequent reverse phenotyping studies across multiple multigenerational pedigrees demonstrated that heterozygous and homozygous carriers consistently show delays in bedtime, midpoint of sleep, and awakening times, alongside physiological shifts like delayed morning bowel movements. Later research also observed behavioral endophenotypes, noting statistical co-occurrence with attention deficit/hyperactivity disorder (ADHD) traits. The evidence is rated strong due to consistent co-segregation in multi-generational kindreds, reproducible cellular kinetics, and replication across independent cohorts.
Population Distribution and Ancestry Frequencies
In global population reference databases such as gnomAD and the 1000 Genomes Project, rs184039278 is an uncommon variant, with overall global minor allele frequencies reported around 0.1% to 0.4%. However, its distribution displays marked ancestry-specific variation. In non-Finnish European populations, the minor allele frequency ranges between approximately 0.3% and 0.6%, meaning as many as 1 in 75 to 1 in 150 individuals in certain European groups carry at least one copy. Furthermore, population screenings identified enrichment in specific demographics, reaching frequencies around 3% in cohorts of Ashkenazi Jewish ancestry. The variant is notably rarer across East Asian, African, and indigenous populations. Because the allele acts in an autosomal dominant fashion with high penetrance, even low population frequencies make it an unusually common monogenic contributor to human circadian phase variation.
Interpreting Results and Practical Considerations
Knowledge of rs184039278 carrier status provides biological insight into an individual's natural circadian tendencies, but it cannot be used alone as a clinical diagnosis. Delayed sleep phase disorder remains a clinical diagnosis based on history, actigraphy, and sleep logs, rather than genotype alone. Finding that one carries an altered allele indicates a strong predisposition toward an evening chronotype, commonly known as an extreme 'night owl.' Readers cannot alter their genetic makeup, but those struggling with morning social requirements may benefit from structured sleep hygiene, strategic morning light exposure, or consultation with a board-certified sleep specialist. Genetic findings should never replace professional medical evaluations or guide off-label pharmacological therapies without clinician oversight.
How common is this variant?
The rs184039278 variant has an overall global minor allele frequency of approximately 0.1% to 0.4%, rising to 0.3%-0.6% in non-Finnish Europeans and up to 3% in Ashkenazi Jewish populations.
Frequently asked questions
Does having the rs184039278 variant guarantee I will have delayed sleep phase disorder?
No single genetic variant guarantees a clinical condition. While rs184039278 acts in an autosomal dominant manner with high penetrance, real-world symptoms depend heavily on environmental zeitgebers like morning sunlight, occupational schedules, and sleep hygiene practices.
How does the CRY1 alteration make someone an extreme night owl?
The variant causes skipping of exon 11, creating a CRY1 protein that binds tightly to core transcription factors and takes longer to release its repression. This molecular delay lengthens the internal circadian day, pushing natural sleepiness and awakening times significantly later than average.
Can commercial genetic tests accurately identify this variant?
Many direct-to-consumer genotyping microarrays do not include rare or splice-site intronic variants such as rs184039278. Whole-genome or whole-exome sequencing typically captures the variant, but any health-related findings should be confirmed with clinical-grade diagnostic assays.
Is this variant linked to conditions other than sleep disorders?
Published studies have observed that carriers of rs184039278 have an increased statistical association with attention deficit/hyperactivity disorder (ADHD) and alterations in metabolic timing, such as delayed morning digestion.
Sources & further reading
Educational information only, last refreshed 9/7/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs184039278?
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 CRY1
This intronic variant in the CRY1 gene is associated with delayed sleep-wake phase disorder (DSWPD) and has been linked to variations in glycemic parameters and insulin resistance.
This splice donor mutation (c.1657+1G>A) causes exon 11 skipping, leading to an overactive repressor complex and familial delayed sleep phase disorder.
Variant in the CRY1 gene, which encodes a core component of the circadian clock, associated with sleep timing and delayed sleep phase.
Dominant splice-site mutation (c.1657+3A>C) in CRY1, resulting in skipping of exon 11 and associated with delayed sleep-wake phase disorder (DSWPD).
Variant in the CRY1 locus associated with sleep timing and circadian rhythm traits; distinct from rare high-penetrance mutations.
Cryptochrome 1 variant linked to sleep-wake timing variations and subjective poor sleep phenotypes.