An Australian study of 2012 has linked vasovagal syncope, fainting, predisposition to genetics. Samuel Berkovic and colleagues suggest that fainting must have a strong genetic component involving multiple genes and used a twin study to prove it.
Vasovagal syncope or fainting is a loss of consciousness usually brought on by the sight of blood, injury, pain, or the like. This is due to hypoperfusion and resulting low oxygenation of the brain. Common presyncope signs include sweating, nausea, weakness, and temporary loss of feeling.
Twins that participated in this study were monozygotic, “identical twins” that came from one egg and sperm, or dizygotic, twins that came from two separate egg/sperm combinations.
In the study, fifty-one same sex twin pairs where at least one twin had syncope were interviewed via phone questionnaire. Questions were asked about their family history and prevalence of syncope. The researchers assigned a score of 1 to 5 for syncopic features of each participant.
– 1 = Presyncope episodes exclusively
– 2 = One syncope episode
– 3 = Two syncope episodes & at least one occurring in exceptional circumstances (ie. malnourishment)
– 4 = Up to three syncope episodes
– 5 = More than three syncope episodes
57% of the individuals exhibited typical vasovagal syncope triggers. Monozygotic twins presented with more scores of 4 and 5 indicating higher rates of syncope than did dizygotic twins (P=0.06). 12 of 19 pairs of monozygotic twins indicated few to no close relatives having syncopic episodes.
With higher rates of vasovagal syncope shown between monozygotic twins and not individuals with more distant genetic parallels, this study strong supports the notion of a genetic component behind fainting. Further studies may be done to find those genes, so gene therapy targets can be identified.
Then even med students who just can’t watch a patient’s leg get cut open (no matter how many times they see it) will be able to continue pursuing their dream without fear of fainting.
Karl Martin Klein, San San Xu, Kate Lawrence, Alexandra Fischer, Samuel F. Berkovic. Evidence for genetic factors in vasovagal syncope, A twin-family study. Neurology, 2012.