rs56051278 — GPD2

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.