Sun sneezing, as name suggests is a photo sneeze reflex or better said a naso-ocular reflex caused by the exposure of an individual to bright light, so Photosneezia is another name came from. Claimed to be affecting 18 - 35 percent of world's population which is quite sizeable number as 1 in 4 persons are sun sneezers, whose exact physiology is yet to be explained.
It is well recorded in history by Aristotle and others but was less understood until recently.
Some believe that it may have evolutionary advantages for the cave dwellers in terms of spreading of pathogens present in their naso-pharynx, to their fellow cohabitants. It doesn't fits that way because we all should have had this in our DNA.
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| Rock Garden, Chandigarh, India |
By 1980s it was established as a heritable autosomal dominant trait, is now called ACHOO syndrome (Autosomal-Dominant Compelling Helio-Opthalmic Outbursts), caused by single-nucleotide polymorphism on Chromosome 2, where a single base Adenine (purine) is replaced by Cytosine (pyrimidine) on DNA due to random mutation.
Being of dominant nature (name; the C allele on the rs10427255 SNP), it expresses itself even if being transmitted by the single parent through Chromosome 2 (location; 146,125,523).
Physiology is simple as Opthalmic branch (Optic nerve) of Trigeminal nerve (longest Cranial nerve) inhances the irritability of the Maxillary branch to get sneeze.
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