rs1554483 — CLOCK

CLOCK rs1554483 — An Intronic Metabolic Risk Variant in the Master Circadian Regulator

The CLOCK gene (Circadian Locomotor Output Cycles Kaput) sits at the top of the mammalian circadian hierarchy. CLOCK protein¹¹ CLOCK protein
A basic helix-loop-helix transcription factor encoded on chromosome 4 that heterodimerizes with BMAL1 to drive 24-hour gene expression rhythms across virtually every tissue in the body heterodimerizes with BMAL1 and binds E-box elements in the promoters of core clock genes including Per1, Per2, Cry1, and Cry2, generating the transcription-translation feedback loop that keeps cellular time. This same molecular oscillator gates metabolic processes — glucose uptake, lipid synthesis, and hormone secretion all oscillate under circadian control.

The rs1554483 variant (chr4:55,455,650, GRCh38) lies deep within an intron of CLOCK, approximately 100 kb from the better-known 3'UTR variant rs1801260. Although it does not alter any amino acid and its precise molecular mechanism has not been characterized at single-nucleotide resolution, it forms part of a two-variant haplotype with rs4864548 that has been replicated across multiple studies as a risk marker for obesity, non-alcoholic fatty liver disease (NAFLD), and metabolic syndrome — particularly in the context of circadian disruption from shift work.

The Mechanism

rs1554483 is an intron variant²² intron variant
A nucleotide change within a non-coding intron; may affect splicing efficiency, enhancer elements, or gene expression level without altering the protein sequence directly in one of CLOCK's 16 annotated transcript isoforms. Its molecular effect has not been characterized in cell-based assays, but given that CLOCK's intronic regulatory landscape contains numerous enhancer elements and splice-regulatory sequences, plausible mechanisms include altered intronic enhancer activity³³ intronic enhancer activity
Enhancers within introns can loop to interact with the promoter and regulate transcription levels; variants in these regions can modulate expression in a tissue-specific manner or subtle effects on CLOCK mRNA splicing efficiency.

What is better established is the biological consequence: disrupted CLOCK function compromises the timing of metabolic gene expression. Mice with circadian clock disruption — including CLOCK mutant lines — develop obesity, hyperlipidemia, hyperglycemia, and fatty liver on standard chow, demonstrating that the circadian machinery directly controls energy balance. Human intronic CLOCK variants that alter expression levels or isoform balance in metabolically relevant tissues (liver, adipose, hypothalamus) are mechanistically plausible candidates for the metabolic associations observed in the epidemiological data.

The Evidence

Obesity and haplotype risk. Sookoian et al. (2008)⁴⁴ Sookoian et al. (2008)
Sookoian S et al. Genetic variants of Clock transcription factor are associated with individual susceptibility to obesity. Am J Clin Nutr, 2008 genotyped six tag SNPs across CLOCK in 1,106 adults (715 lean, 391 obese/overweight). The rs1554483G — rs4864548A paired haplotype was found in 47% of obese individuals versus 41% of lean controls, corresponding to a 1.8-fold odds for overweight or obesity (P = 0.011). Among the individual SNPs, rs1554483 showed one of the four significant obesity associations.

NAFLD and liver disease. Sookoian et al. (2007)⁵⁵ Sookoian et al. (2007)
Sookoian S et al. Common genetic variations in CLOCK transcription factor are associated with nonalcoholic fatty liver disease. World J Gastroenterol, 2007 studied 136 NAFLD patients and 64 healthy controls (91 patients with liver biopsies). rs1554483 was among the variants showing a significant association with both clinical NAFLD spectrum (P = 0.0399) and fibrosis score (P = 0.027). CLOCK haplotype frequencies differed significantly between NAFLD and healthy groups (P = 0.0097), placing this variant within a haplotypic context linked to fatty liver susceptibility and progression.

Metabolic syndrome in shiftworkers. Sookoian et al. (2010)⁶⁶ Sookoian et al. (2010)
Sookoian S et al. Gene-gene interaction between serotonin transporter (SLC6A4) and CLOCK modulates the risk of metabolic syndrome in rotating shiftworkers. Chronobiol Int, 2010 studied 856 men (518 dayworkers, 338 shiftworkers) and found that rotating shiftworkers who were homozygous for the serotonin transporter short allele (SLC6A4 S/S) and carried the CLOCK rs1554483G-rs4864548A haplotype had the highest values for diastolic blood pressure (P = 0.006), systolic blood pressure (P = 0.001), plasma triglycerides (P = 0.033), and number of metabolic syndrome components (P = 0.01). This study established that the metabolic risk conferred by this CLOCK haplotype is amplified when circadian rhythms are externally disrupted by rotating shift schedules.

Alzheimer's disease susceptibility. Chen et al. (2013)⁷⁷ Chen et al. (2013)
Chen Q et al. Functional CLOCK gene rs1554483 G/C polymorphism is associated with susceptibility to Alzheimer's disease in the Chinese population. J Int Med Res, 2013 found that the G allele was enriched among Alzheimer's patients (n = 130) compared to healthy controls (n = 188) in a Chinese cohort, specifically in individuals who did not carry the APOE ε4 allele. APOE ε4 itself is so strongly linked to AD risk that it may mask the CLOCK signal in carriers. This association is preliminary and requires replication in larger, ethnically diverse samples.

Population distribution of the risk haplotype. Flores et al. (2023)⁸⁸ Flores et al. (2023)
Flores SV et al. Prevalence of the GA risk haplotype of rs1554483 and rs4864548 polymorphisms of the CLOCK gene associated with obesity. Nutr Hosp, 2023 calculated haplotype frequencies across 26 world populations using 1000 Genomes data, finding that the rs1554483G-rs4864548A haplotype ranges from 17.9% in African populations to 57.4% in East Asian populations — a three-fold range that reflects strong continental stratification and may contribute to population differences in metabolic disease risk.

Practical Actions

The metabolic associations for the G allele are clearest in two high-risk contexts: shift work (where circadian disruption amplifies the genetic risk) and late eating patterns (where the circadian-metabolic axis is chronically misaligned). For G allele carriers, the evidence supports interventions that strengthen circadian alignment — principally consistent meal timing and protection of regular sleep-wake schedules.

For CG and GG carriers in occupations with rotating shifts, the Sookoian et al. 2010 data indicate that the combination of genetic predisposition and circadian disruption from shift work carries a meaningfully higher metabolic syndrome risk. Strategies that anchor the circadian clock — fixed anchor sleep times, bright light on starting shifts, and structured meal windows — are particularly relevant.

The NAFLD association suggests that liver-specific circadian metabolism may be altered by this haplotype. Avoiding prolonged fasting followed by large evening meals — a pattern that stresses hepatic lipid handling — is particularly relevant for G allele carriers concerned about liver health.

Interactions

The most important interaction documented for rs1554483 is with rs4864548, the second component of the obesity risk haplotype. Neither SNP alone showed as strong an effect as the paired haplotype in the Sookoian 2008 study, indicating haplotypic synergy⁹⁹ haplotypic synergy
Two variants that are more strongly associated with a phenotype together than either is individually, suggesting they tag the same functional effect or act in cis on the same allele. The risk haplotype (G at rs1554483 + A at rs4864548) should be considered together rather than evaluating either variant in isolation.

The interaction with SLC6A4 (serotonin transporter) variants in the context of shift work points to a broader gene-environment interaction where serotonin-circadian crosstalk amplifies metabolic risk. CLOCK and the serotonin transporter are both expressed in hypothalamic nuclei that regulate energy balance, and their combined dysregulation may compound appetite and metabolic disturbances.

rs1554483 should also be read alongside rs1801260 (CLOCK 3111T>C), which is mechanistically characterized as a miR-182 binding site variant affecting CLOCK mRNA stability and is the primary CLOCK variant linked to evening chronotype. The two variants are in different regions of the gene (rs1801260 in the 3'UTR; rs1554483 in an intron) and tag independent haplotype blocks, meaning they can independently contribute to CLOCK function — a carrier of both risk alleles would have two separate CLOCK-perturbing variants.