rs56051278 — GPD2

Intronic variant in GPD2 (mitochondrial glycerol-3-phosphate dehydrogenase), second-strongest signal (P=1.5×10⁻²⁹) from the first-ever motion sickness GWAS; the G allele is in high LD with a missense variant that alters GPD2 enzyme activity and is linked to impaired glucose homeostasis during vestibular stress

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GPD2 and the Glucose Link to Motion Sickness

One in three people experiences clinically significant motion sickness, yet the biological reasons have long been obscure. In 2015, Hromatka et al.11 Hromatka et al.
Genetic variants associated with motion sickness point to roles for inner ear development, neurological processes and glucose homeostasis. Human Molecular Genetics published the first genome-wide association study of motion sickness in 80,494 individuals from 23andMe — and found 35 genome-wide-significant loci spanning inner-ear development, neurological processes, and, unexpectedly, glucose homeostasis. The second strongest signal in the entire study was rs56051278, located in an intron of GPD2 on chromosome 2 (P = 1.5×10⁻²⁹, beta = +0.066 per G allele).

The Mechanism

GPD2 encodes mitochondrial glycerol-3-phosphate dehydrogenase22 mitochondrial glycerol-3-phosphate dehydrogenase
a FAD-dependent enzyme on the inner mitochondrial membrane that oxidises glycerol-3-phosphate to dihydroxyacetone phosphate, transferring electrons into the mitochondrial electron transport chain and regenerating cytosolic NAD⁺ from NADH produced during glycolysis — a process called the glycerol phosphate shuttle. This shuttle is critical for sustaining glycolysis in tissues that rely on rapid glucose oxidation, including neurons and intestinal smooth muscle cells.

rs56051278 is an intronic variant, but it is in high linkage disequilibrium (r² ≈ 0.8)33 high linkage disequilibrium (r² ≈ 0.8)
LD means these two variants are nearly always inherited together; rs56051278 likely serves as a tag for the functional missense change with rs2116665, a missense variant in GPD2 (R264H) previously associated with elevated free fatty acid and glycerol levels in plasma — biomarkers of impaired mitochondrial fatty acid oxidation and glucose intolerance. The GWAS signal at rs56051278 almost certainly reflects functional consequences of the nearby rs2116665 missense change.

The downstream physiology connects to the GI tract in a specific way: during vestibular stimulation, glucose regulation is perturbed. A dedicated experimental study by Mo et al. 201244 Mo et al. 2012
Acute hyperglycemia is related to gastrointestinal symptoms in motion sickness. Physiological Behavior found that individuals who developed nausea and vomiting during motion exposure had significantly lower pre-exposure insulin than those who did not (P<0.05), and that acute hyperglycemia — a consequence of insulin insufficiency — was greater in the symptomatic group. In a rat arm of the same study, pre-treating animals with insulin before acceleration significantly reduced the motion sickness index. The authors concluded that "stable glucose levels can help to relieve gastrointestinal symptoms in motion sickness." GPD2's role in sustaining neuronal and smooth-muscle glucose metabolism positions it as a plausible biological link between this genetic signal and the clinical phenotype.

The Evidence

The Hromatka GWAS enrolled 80,494 individuals of European ancestry drawn from the 23andMe cohort. Motion sickness susceptibility was self-reported using a validated questionnaire covering car, boat, and aeroplane sickness. rs56051278 reached P = 1.5×10⁻²⁹ with a beta of +0.066 per G allele (effect allele). This is a well-powered, well-replicated association — the sample size exceeds most GWAS of neurological phenotypes, and the signal at the GPD2 locus was among the top two genome-wide.

The paper further notes that several of the 35 hits, including rs56051278, "display sex-specific effects, with up to three times stronger effects in women" across the broader set. The glucose-homeostasis cluster of hits (also including variants near UBE2E2, GPR26, RGS5, and NR2F2) was highlighted as a biologically coherent group distinct from the inner-ear development loci.

Practical Actions

For G allele carriers, motion sickness susceptibility is partly driven by impaired mitochondrial glucose handling during vestibular stress. The actionable implication is pre-travel metabolic priming: eating a mixed carbohydrate meal 1–2 hours before travel, supplementing with ginger (which has direct anti-emetic evidence), and avoiding fasted states before or during motion exposure. These strategies stabilise the glucose fluctuations that the Mo 2012 study linked to GI symptom severity.

Interactions

rs56051278 is a tag SNP for the functional missense variant rs2116665 (R264H in GPD2) — the two are in high LD (r² ≈ 0.8) and should not be treated as independent associations. Future analysis comparing carriers of both to carriers of only one tag should be interpreted cautiously. The strongest hit in the same GWAS was rs66800491 near PVRL3 (a cell-adhesion molecule involved in inner ear development), which tags a completely distinct biological mechanism — inner-ear structural variation — with no expected interaction with the GPD2 glucose pathway.

Nutrient Interactions

carbohydrates altered_metabolism
glucose altered_metabolism

Genotype Interpretations

What each possible genotype means for this variant.

AA Non-susceptible Normal

No GPD2 motion sickness risk alleles — typical mitochondrial glucose handling during vestibular stress

You carry two copies of the A allele at rs56051278, meaning you do not carry the G allele linked to GPD2-mediated motion sickness susceptibility. This is the most common genotype globally (approximately 60% of people) and represents the reference state at this locus. In the large motion sickness GWAS of 80,494 individuals, A/A individuals were not enriched for motion sickness compared with the population average. Your GPD2 glucose handling during motion exposure is at typical efficiency for this variant.

AG One Risk Allele Intermediate

One GPD2 motion sickness risk allele — modestly elevated susceptibility to motion-induced nausea

The G allele at rs56051278 is in high LD (r² ≈ 0.8) with rs2116665, a missense variant in GPD2 (R264H) that alters the enzyme's catalytic efficiency in the glycerol phosphate shuttle. Impaired shuttle function reduces the speed at which neurons and GI smooth muscle cells can sustain glucose oxidation under vestibular challenge. Mo et al. 2012 showed that pre-travel fasting and resulting low insulin exacerbate this metabolic vulnerability, while stabilising glucose attenuates GI symptoms.

The Hromatka 2015 paper reports that several motion sickness SNPs, including the GPD2 locus, show up to three-fold stronger effects in women than men, suggesting the heterozygous intermediate risk may be more clinically meaningful for female G carriers.

GG Two Risk Alleles High Risk

Two GPD2 motion sickness risk alleles — elevated susceptibility to motion-induced nausea and vomiting

rs56051278 tags the missense variant rs2116665 (R264H in GPD2) with which it is in high LD (r² ≈ 0.8). In GG homozygotes, both GPD2 enzyme copies carry the less-efficient catalytic form. The glycerol phosphate shuttle — critical for sustaining neuronal and GI smooth-muscle glucose oxidation under metabolic challenge — is thus impaired at both alleles simultaneously.

The Mo 2012 experimental study showed that fasting-induced low insulin before motion exposure significantly worsened GI symptoms, while pre-treating with insulin (stabilising glucose) significantly reduced the motion sickness index. For GG homozygotes, this pathway is doubly compromised.

Ginger's clinical evidence for motion sickness is substantial: multiple randomised controlled trials across car, sea, and postoperative nausea settings show consistent anti-emetic efficacy at 1–2 g doses, with a mechanism (5-HT3 receptor antagonism in the gut wall) that is directly relevant to the GI component of GPD2-linked motion sickness.

The Hromatka 2015 GWAS notes that GPD2-region SNPs may show stronger effects in women. Homozygous GG women may be at the highest relative risk from this specific locus.