Monday, July 13, 2015

ACHOO syndrome - Sun sneezers and the Photic Sneeze Reflex

Do you sneeze when you look at the sky ?

Do you go "Achoo" when you see a bright light ?

Calvin suffers from the ACHOO syndrome or Sun Sneezing

You might be having ACHOO syndrome. Yes, it is the official Acronym for this condition.

Autosomal Dominant Compelling Helio-Ophthalmic Outburst Syndrome (ACHOO)

Autosomal Dominant is the mode of Mendelian Inheritance it follows.

Helio means Sun.

Ophthalmic means related to the eye.

Compelling, Outburst and Syndrome are self explanatory. Made to be so that the acronym says "Achoo"

Sun sneezing affects 18-35% of the population, but it is still not well understood. Its mechanism is still just hypothesis and theories.

The first formal investigation of the reflex was probably made in the early 1950s by a French researcher named Sedan. He discovered that some patients sneezed when he shined his ophthalmoscope, used to examine the retina, into their eyes. His continuing inquiry into six such photic sneezers established that they would also sneeze when exposed to bright sunlight, flash photography, and in one case, an ultraviolet light. In describing the phenomenon, he noted that the sneeze only occurs just as the patient becomes exposed to light; they don't continue to sneeze even if continually awash in the bright glow of the Sun (or an ophthalmoscope).

Since Sedan wasn't able to find any discussion of light-related sneezing in the medical literature, he concluded it must be quite rare. But by the time that physician H C Everett, who seems to have coined the phrase "photic sneeze reflex", wrote about it in the journal Neurology in 1964, it seems as if quite a bit more was known about the condition.
For one thing, it was known to be somewhat more common than Sedan had assumed. Researchers would go on to estimate that it afflicts some 17% to 35% of the world's population: some 23% of medical students in Everett's study, and 24% of blood donors in another.

In 2010, a group of geneticists led by Nicholas Eriksson of the genetic testing company 23andMe identified two single nucleotide polymorphisms, or SNPs, that were associated with the sunny sneeze by assessing the genotypes of nearly 10,000 23andMe customers. These SNPs are alterations to single letters within a person's genetic library. One is called rs10427255 and the other, about which there is somewhat less statistical certainty, is called rs11856995. One of them is located nearby a gene known to be involved in light-induced epileptic seizures, which raises the possibility that there might be some kind of biological link between the two syndromes.

Despite the information that researchers have managed to amass on the subject, nobody quite knows exactly how optical stimulation of the eyes leads to a sneeze, but one possibility is that the eyes and the nose are connected via the fifth cranial, or trigeminal, nerve. Or it could be the result of a process called "parasympathetic generalisation". When a stimulus excites one part of the body's parasympathetic nervous system, other parts of the system tend to become activated as well. So when bright light causes the eye's pupils to constrict, that may indirectly cause secretion and congestion in the nasal mucus membranes, which then leads to a sneeze.

It sounds like it could be a fairly trivial issue but as Benbow pointed out in his 1991 letter, it can actually prove quite dangerous in certain situations. "I found that sudden exposure to sunlight when emerging from a road tunnel of sufficient length is sure to induce a sneeze, with accompanying momentary blindness," he wrote. Sunshine sneezing could also be detrimental for baseball outfielders and high-wire acrobats. Perhaps the need to avoid a mile-high sneeze also gave birth to that great fashion accessory: aviator shades.

What is the treatment for Photic Sneeze reflex or Achoo Syndrome ?

While this phenomenon is poorly understood, recent research has shown that antihistamines like Cetirizine or Fexofenadine being used to treat rhinitis due to seasonal allergies may also reduce the occurrence of photic sneezes in people affected by both conditions.

Some people may find relief by shielding their eyes and/or faces with hats, scarves, and sunglasses.

A study conducted by the School of Optometry at the University of Alabama at Birmingham, found that females represent 67% of photic sneezers, and Caucasians represent 94%. The study also found statistically significant correlations between photic sneezing and the presence of a deviated nasal septum. The study also showed that photic sneezing is more likely to be acquired than inherited.

What is Snatiation ? Do you sneeze after eating ?

A condition called gustatory rhinitis can cause some individuals to sneeze after eating, particularly after the consumption of spicy foods. Stomach fullness is another example of a stimulus that can cause uncontrollable sneezing. Those who exhibit this symptom or disorder, called snatiation, undergo uncontrollable fits of 3–15 sneezes immediately after eating large meals that completely fill the stomach, regardless of the type of food eaten. Snatiation is not believed to be an allergic reaction of any kind. Even less well-understood than photic sneezing and sneezing in response to periocular injection, the trait appears to be inherited in an autosomal dominant fashion

How to prevent Achoo and Snatiation ?

There is currently no definitive way to cure the sneezing fits brought on by the photic sneeze reflex. Photic sneezing can be combated by shielding one's eyes with hats or sunglasses. There are many remedial fixes for sneezing, such as placing a finger horizontally below the nose or holding the nose closed when the beginnings of a sneeze are felt.

Another remedy is to deliberately cause the onset of sneezing in a safe environment before moving into an environment where the condition could be a danger. The person will then be protected as long as the refractory period lasts.

The most helpful way to avoid the risks stated above is to be aware of any inclination to sneeze in response to strange stimuli. If a pilot knows he or she is at risk for experiencing a photic sneeze during a flight, he or she can wear polarized goggles to block out the sun, or at the very least be prepared for a sneeze and have measures planned to minimize the risk from such a sneeze. Any patient with a history of uncontrollable sneezing who requires periocular surgery should tell the doctor or anesthesiologist, so that they can take appropriate measures to minimize the risk of injury in case of a sneeze during the surgical procedure. People who know they have a tendency to experience sneezing fits after consuming a large meal can make an effort to reduce the size of their meals, since snatiation seems to occur only as a result of an extremely full stomach.

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