BTBD9 rs13040366: What Your Genotype Means
The single nucleotide polymorphism rs13040366 is a common non-coding genetic variant located within or near the BTBD9 gene on chromosome 6. In genomic research, this locus has been evaluated for statistical associations with restless legs syndrome (RLS) and periodic leg movements during sleep (PLMS). Evidence linking this specific SNP to trait variation remains limited, serving primarily as a marker of common inherited variation in sleep-related genetic studies.
What each genotype means
Typical risk profile
You carry two copies of the major C allele at this position. Large-scale genetic association studies have found that this genotype is not associated with an increased susceptibility to restless legs syndrome or periodic limb movements during sleep. Because this variant represents a non-coding regulatory factor with limited overall effect, lifestyle, iron levels, and other genomic factors remain the predominant determinants of sleep-related movement symptoms.
Carried by approximately 50% to 55% of individuals globally, making it the most common genotype across most continental populations.
Slightly elevated movement risk
You have one copy of the T allele and one copy of the C allele. In published genome-wide association studies, carrying one T allele has been associated with a modest statistical increase in the risk of restless legs syndrome and periodic leg movements during sleep. However, this is an intronic marker with limited standalone effect size, and having this genotype does not mean you will develop restless legs or sleep disruptions.
Found in approximately 35% to 40% of individuals in global population reference sets such as gnomAD.
Moderately elevated movement risk
You carry two copies of the minor T allele associated with altered BTBD9 regulation. Population studies observe that homozygous carriers have a statistically higher likelihood of experiencing periodic limb movements during sleep and restless legs syndrome compared to non-carriers. Given that the evidence for this specific non-coding variant remains limited and multi-factorial, it represents a predisposing risk factor rather than a diagnosis.
Carried by roughly 5% to 8% of people worldwide, consistent with an overall minor allele frequency of about 0.26.
Genetic Landscape: What rs13040366 Is and Where It Sits
The variant rs13040366 represents a single nucleotide variation mapped to the genomic locus encompassing BTBD9 on the short arm of chromosome 6 (6p21.2). It is classified as a non-coding variant, meaning that it does not alter the amino acid sequence of any encoded protein. Instead, variants in this category lie in intronic or flanking intergenic regulatory sequences, where their potential effects typically involve modulating transcription factor binding, splicing patterns, or regional chromatin architecture. Because rs13040366 is situated in a region characterized by linkage disequilibrium—where neighboring variants are frequently co-inherited—genomic studies often analyze this marker alongside prominent regional tagging variants. Current repository databases such as dbSNP, Ensembl, and gnomAD record this site as a biallelic polymorphism. Because it does not cause a direct disruption to a protein-coding sequence, rs13040366 is understood to function, at most, as a subtle regulatory modifier rather than a high-impact pathogenic mutation.
Biological Context: What Does the BTBD9 Gene Do?
The BTBD9 gene encodes BTB domain-containing protein 9, a conserved protein containing a Broad-Complex, Tramtrack, and Bric-à-brac (BTB/POZ) domain. This structural domain commonly mediates protein–protein interactions, ubiquitination processes, and the regulation of gene transcription. BTBD9 is widely expressed across human tissues, showing notable expression levels within the central nervous system, including the cerebellum and subcortical regions involved in sensorimotor coordination. Functional investigations in neurobiology and model organism systems have implicated BTBD9 in iron homeostasis, central dopaminergic neurotransmission, and synaptic plasticity. Animal models with disrupted Btbd9 function display fragmented sleep patterns, motor restlessness during resting periods, and subtle alterations in striatal dopamine pathways. These physiological pathways closely align with the clinical biology of nocturnal sensorimotor disorders, making BTBD9 one of the key candidate genes investigated in sleep-related neurological phenotypes.
Research Associations: Restless Legs and Sleep Movement
Genome-wide association studies (GWAS) have established the BTBD9 locus on chromosome 6p21 as a major susceptibility region for restless legs syndrome (RLS) and periodic leg movements during sleep (PLMS). In published cohorts, variation across this genomic block has been linked to elevated night-time limb movement indices and an increased population-level predisposition to the uncomfortable resting urges that define RLS. However, the specific evidence directly connecting rs13040366 to sleep-related traits is classified as limited. While prominent haplotype markers in BTBD9 (such as rs3923809 and rs9357271) have shown genome-wide significance across multiple European and international cohorts, individual neighboring non-coding markers like rs13040366 frequently demonstrate weaker or purely correlative statistical signals. Studies have observed inconsistent effect sizes across differing ancestral backgrounds, largely due to variations in regional linkage disequilibrium. Consequently, possessing an association-linked allele at rs13040366 indicates a modest shift in statistical risk rather than a definitive causal effect.
Actionability: What You Can and Cannot Do with This Information
Learning your genotype at rs13040366 provides personal genomic insight, but it carries clear clinical limitations. Because this variant represents a non-coding polymorphism with limited independent evidence, it cannot be used to diagnose restless legs syndrome, predict sleep quality, or assess iron deficiency. Complex neurological and sleep phenotypes are polygenic, shaped by dozens of subtle genetic loci interacting alongside lifestyle factors, systemic iron levels, caffeine consumption, pregnancy, and peripheral nerve health. If you experience persistent discomfort, nocturnal tingling, or an irresistible urge to move your limbs at rest, this genetic marker should not guide self-treatment. Medication response, dopaminergic therapies, or iron supplementation regimens require professional clinical oversight. Anyone experiencing disrupted sleep should review their symptoms with a physician or sleep specialist rather than altering lifestyle or pharmacological routines based on an individual SNP readout.
How common is this variant?
In global population datasets from gnomAD, the minor allele frequency (MAF) for rs13040366 is approximately 0.26 (26%), with allele frequencies varying moderately across ancestral populations.
Frequently asked questions
Does having a risk genotype at rs13040366 mean I will develop Restless Legs Syndrome?
No. Complex traits like restless legs syndrome depend on many genetic loci as well as environmental factors such as overall health, medications, and iron levels. Carrying an associated genotype only reflects a slight statistical correlation in research cohorts and cannot cause or diagnose RLS on its own.
What is the difference between RLS and periodic leg movements during sleep (PLMS)?
Restless legs syndrome (RLS) is a sensory-motor condition characterized by uncomfortable limb sensations and an urge to move during wakeful rest. In contrast, periodic leg movements during sleep (PLMS) involves involuntary, repetitive jerking or twitching movements of the legs while sleeping. Many individuals with RLS also have PLMS, and BTBD9 has been investigated in relation to both phenotypes.
Should I start taking iron or dopamine supplements based on this result?
No. You should never start iron supplements, dopamine-affecting supplements, or any medications without clinical lab testing and a physician's guidance. While the BTBD9 pathway interacts with cellular iron and dopamine biology, genetic data cannot determine your actual blood ferritin levels or therapeutic needs.
Why is the evidence for rs13040366 described as limited?
The evidence is categorized as limited because rs13040366 is a non-coding variant that primarily reflects regional correlation (linkage disequilibrium) rather than confirmed biological causation. Most primary GWAS signals in BTBD9 focus on distinct lead variants, and association studies for secondary SNPs often show modest or ancestry-specific results.
Sources & further reading
Educational information only, last refreshed 9/10/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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This variant in the BTBD9 gene is strongly associated with susceptibility to restless legs syndrome (RLS).
Intronic variant strongly associated with restless legs syndrome (RLS) susceptibility and periodic limb movements during sleep (PLMS), mediating altered iron homeostasis.
A prominent non-coding variant in BTBD9 strongly conferring risk for periodic limb movements during sleep and restless legs syndrome.
Genome-wide significant intronic susceptibility variant in BTBD9 strongly predisposing individuals to restless legs syndrome and periodic limb movements in sleep.
A regulatory intron variant in BTBD9 strongly associated with periodic limb movements in sleep.
Intronic risk variant in BTBD9 strongly associated with periodic limb movement in sleep (PLMS) and restless legs syndrome (RLS).