Photic sneeze reflex

The Photic sneeze reflex, alternatively referred to as Autosomal Dominant Compelling Helio-Ophthalmic Outburst (ACHOO) syndrome or photosneezia, is an intriguing physiological phenomenon. It is a reflex condition which induces sneezing as a response to various stimuli, prominently exposure to bright lights or periocular injection. This unique reflex is estimated to be present in approximately 18–35% of the global population.

Autosomal dominant inheritance

Genetics

As its alternate name, ACHOO syndrome, suggests, this condition is considered to be autosomal dominant, meaning that the inheritance of a single copy of the 'sneeze gene' from an affected parent is sufficient to express the trait. However, the exact genetic basis remains elusive, as the specific gene or genes involved have not been definitively identified.

Mechanism

The precise mechanism underlying the photic sneeze reflex is not fully understood. However, it is hypothesized that the phenomenon might result from some form of cross-talk or confusion within the trigeminal nerve, which is the primary facial sensory nerve and has been associated with the sneeze reflex. Light-induced sneezing could be due to an overstimulation or abnormal sensitivity of this nerve in response to intense light stimulation, but further research is needed to confirm this theory.

Triggers and Symptoms

While exposure to bright light is the most commonly known trigger for the photic sneeze reflex, certain individuals might experience sneezing induced by other stimuli, such as fullness of the stomach, periocular injection, or sudden changes in environmental temperature.

Diagnosis and Management

Diagnosis of the photic sneeze reflex is typically based on the characteristic history of sneezing in response to bright light or other known triggers. No specific diagnostic tests exist for this condition, nor is there a definitive cure. Management primarily involves awareness and avoidance of known triggers. In scenarios where exposure to bright light is unavoidable, wearing sunglasses or hats might prove beneficial.

Implications

The photic sneeze reflex is generally benign and does not lead to significant health problems. However, it can be potentially hazardous in certain situations requiring visual concentration, such as driving or operating machinery, where an unexpected sneezing episode could cause momentary visual obstruction.

Future Research

Future research will hopefully shed more light on the genetic and neurological mechanisms underlying the photic sneeze reflex, which could further our understanding of not only this intriguing phenomenon but also of more general aspects of neurology and sensory processing.

References

• Collie, WR; Pagon, RA; Hall, JG; et al. (2002). "ACHOO syndrome (Autosomal Dominant Compelling Helio-Ophthalmic Outburst syndrome)". In Adam, MP; Ardinger, HH; Pagon, RA; et al. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle. PMID 20301501.
• Langer, N; Beeli, G; Jäncke, L (2010). "When the Sun Prickles Your Nose: An EEG Study Identifying Neural Bases of Photic Sneezing". PLOS ONE. 5 (2): e9208. Bibcode:2010PLoSO...59208L. doi:10.1371/journal.pone.0009208. PMC 2820579. PMID 20169156.
• Everett, HC (1964). "Sneezing in response to light". Neurology. 14 (5): 483. doi:10.1212/wnl.14.5.483. PMID 14171224.

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