Photic sneeze reflex

The explanation why some people tend to sneeze when exposed to bright light remains an enigma. There are indications that certain variants may increase the predisposition to this particular trait.

The "photic sneeze reflex" is a characteristic of some people who tend to sneeze when they move from relative darkness to bright light, often sunlight (e.g., when exiting a tunnel). Once the eyes have adapted to the brightness the sneezing stops. This condition occurs in about one in four Caucasians and is thought to have a hereditary component.

The exact cause of this reflex and whether it has any physiological relevance is unknown, but it is thought to be due to an electrical process in which light stimulates several nerves involved in the sneeze reflex.

The fact of responding involuntarily with a sneeze when exposed to bright light is a trait that possibly follows an autosomal dominant pattern of inheritance, although studies are inconclusive and suggest that more genes may be involved.

The genome-wide association study carried out by Eriksson et al. suggests that this trait is associated with a region of chromosome 2 (2q22.3), close to the ZEB2 gene.

It has been observed that certain variants with a low frequency in the general population found in the ZEB2 gene produce Mowat-Wilson syndrome, which manifests with seizures and photosensitivity, among other symptoms. This suggests that there may be a relationship between photosensitive epileptic seizures and the photic sneeze reflex.

Number of observed variants

13.5 million variants

Number of variants analyzed in the study

1 variant

Bibliography

Eriksson N, Macpherson JM, Tung JY, Hon LS, Naughton B, Saxonov S, et al. Web-based, participant-driven studies yield novel genetic associations for common traits. PLoS Genet. 2010;6(6):1–20.

Wang M, Sun X, Shi Y, Song X, Mi H. A genome-wide association study on photic sneeze reflex in the Chinese population. Sci Rep. 2019 Mar 21;9(1):4993.

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