rs2153535 — BLOC1S5

MUTED/BLOC1S5 — Inner Ear Otolith Biology and Motion Sickness Susceptibility

Motion sickness is not a matter of imagination or willpower — it has a measurable genetic architecture. The largest GWAS of motion sickness to date (80,494 individuals from 23andMe) identified 35 genome-wide significant loci, and the variant near MUTED on chromosome 6 stands out for pointing directly to the sensory mechanism that makes motion perception possible in the first place: otoliths¹¹ otoliths
calcium carbonate crystals embedded in a gel matrix within the utricle and saccule of the inner ear; they shift under gravity and linear acceleration, bending hair cells to signal head movement to the brain.

MUTED (also called BLOC1S5) encodes a subunit of the biogenesis of lysosome-related organelles complex 1 (BLOC-1). In mice, the homolog of MUTED specifically controls the synthesis of otoliths in the vestibular labyrinth — and mice with muted mutations develop deficient otoconia, the calcium carbonate crystals that constitute the otolith mass, with proportionally impaired gravity receptor responses.

rs2153535 is a regulatory variant approximately 300 kilobases downstream of BLOC1S5 on chromosome 6p24.3. The G allele reaches genome-wide significance for motion sickness susceptibility at p = 2.7×10⁻¹⁸, with a per-allele beta of 0.046. The G allele is common globally (approximately 40%) but shows notable variation across ancestries: nearly 50% in Europeans, only 22% in East Asians.

The Mechanism

The BLOC-1 complex regulates trafficking of membrane proteins to lysosome-related organelles — in the inner ear, this includes the vesicular machinery needed to deposit calcium carbonate onto the otolith membrane during development and maintenance. Impaired BLOC1S5 function in mouse models results in reduced or abnormal otoconia, meaning the gravity-sensing mass in the utricle and saccule is diminished.

The consequence is not deafness — the auditory cochlea is unaffected by these mutations — but a selective impairment of the otolith organs' ability to transduce gravity and linear acceleration signals faithfully. When the vestibular signal is weak or asymmetric, the brain receives ambiguous information about head position and movement. Physiological studies confirm this²² Physiological studies confirm this
Singh et al. 2014 demonstrated elevated vestibular evoked myogenic potential thresholds and higher inter-aural asymmetry ratios in motion sickness-susceptible individuals compared with controls: reduced or asymmetric otolith function is the likely mechanism linking genetic vestibular variants to motion sickness susceptibility.

Motion sickness itself arises from sensory conflict — the brain receives inconsistent signals from the vestibular system, visual system, and proprioception about what motion is occurring. A vestibular system with reduced otolith fidelity generates a noisier signal, increasing the probability of that conflict threshold being crossed during passive movement (car, boat, plane, VR).

The Evidence

Hromatka et al. 2015³³ Hromatka et al. 2015
Genetic variants associated with motion sickness point to roles for inner ear development, neurological processes and glucose homeostasis. Human Molecular Genetics is the founding study: 80,494 participants from 23andMe, 35 genome-wide significant loci, P = 2.7×10⁻¹⁸ at rs2153535. The propensity score built from all 35 SNPs explained 2.9% of variance in motion sickness; individuals in the top 5% had 6.37-fold increased odds of frequent motion sickness. Sex-specific effects were substantial — effects up to three times stronger in women — consistent with known clinical observations that women are more frequently and severely affected by motion sickness.

The genetic overlap between motion sickness and vertigo is supported by Skuladottir et al. 2021⁴⁴ Skuladottir et al. 2021
A genome-wide meta-analysis uncovers six sequence variants conferring risk of vertigo. Communications Biology (48,072 vertigo cases, 894,541 controls), which found that eight motion sickness variants from Hromatka 2015 also associated with vertigo — suggesting shared vestibular pathway architecture underlies both conditions.

The causal biological link between MUTED gene function and inner ear gravity sensing is supported by Jones et al. 2004⁵⁵ Jones et al. 2004
Gravity receptor function in mice with graded otoconial deficiencies. Hearing Research: otoconial-deficient mice including the muted strain showed graded vestibular response impairment proportional to their degree of otolith loss.

Practical Actions

Motion sickness susceptibility from this locus is a property of the vestibular system's baseline signal fidelity, not something modifiable by supplements. The actionable strategies are behavioral and pharmacological: positioning to minimize sensory conflict (front-seat travel, horizon-facing orientation), scopolamine patches before anticipated exposure, and vestibular habituation training (a structured exposure protocol used in aerospace medicine to increase motion sickness threshold). There is emerging evidence that these training protocols produce lasting neuroadaptation even in genetically susceptible individuals.

Interactions

The MUTED locus is one of 35 genome-wide significant motion sickness loci from Hromatka 2015. Other major loci include rs66800491 near PVRL3 (eye development, strongest hit at p = 4.2×10⁻⁴⁴) and rs1195218 near AUTS2 (autism spectrum/neurodevelopment, p = 4.5×10⁻²²). The combination of multiple motion sickness risk alleles compounds susceptibility — the polygenic score across all 35 loci explains 6.37-fold odds in the top 5% versus the bottom 5%. The MUTED locus does not interact with specific drugs through pharmacogenomic mechanisms, but G allele homozygotes who respond poorly to scopolamine are likely best served by vestibular habituation training as an alternative prevention strategy.

The overlap between motion sickness and migraine susceptibility (Hromatka 2015 confirmed the genetic correlation) suggests that vestibular migraine — where migraine attacks trigger vestibular symptoms — may be especially relevant for carriers of both MUTED-region risk alleles and known migraine susceptibility variants.