American researchers have discovered that two types of strabismus, esotropia and exotropia, may have common genetic risk factors.
- Esotropia is a case of strabismus characterized by an inward-facing eye. Exotropia is a specific form where one eye is deviated outward.
- Duplications on chromosomes 2, 4, and 10 present in people with esotropia have also been found in adults with exotropia.
- Patients with duplication had a higher mean amplitude of deviation, were more likely to have constant exotropia, and a higher rate of strabismus surgery.
Strabismus is when the eyes are no longer coordinated to look at the same object together. This vision disorder is characterized by the deviation of one eye in relation to the other. There are several types of strabismus: hypertropia results in an upward rotation of the eye and hypotropia downwards. Esotropia is a case characterized by an inward-facing eye. As for exotropia, it is a form where one eye is deviated outwards.
Genetic samples from 234 adults with exotropia were analyzed
This eye disorder affects up to 4% of the population and is common in children. Several environmental factors, including prematurity, low birth weight, and smoking during pregnancy, have been associated with esotropia and exotropia. However, “it is not known whether these two types of strabismus share genetic risk factors”, indicated scientists from Harvard Medical School (United States). This is why they carried out work published in the journal JAMA Ophthalmology.
For the purposes of their study, the team relied on a previous cohort from the university which had identified three recurrent gene duplications increasing the risk of esotropia in patients. To see if variants of these three chromosomes were specifically associated with esotropia or if they had a more general link with strabismus, she analyzed genetic samples from 234 people who were followed for 18 years. The participants had exotropia, while their family members had other types of strabismus or not.
Esotropia, exotropia: a common genetic risk for both forms of strabismus
“When we first started looking at this, we thought maybe we would find that a specific gene was deleted and that would tell us that this gene was important. But that’s not what we found.” said Mary Whitmanwho participated in the research.
The results showed that esotropia-associated gene duplications on chromosomes 2, 4, and 10 were seen in 1.7%, 3.0%, and 6.0%, respectively, of people with exotropia. “We think these regions that are duplicated probably affect gene regulation.” Patients with duplication had greater exotropia, a higher frequency of constant deviation, and higher rates of requiring strabismus surgery.
“Identify people at risk before they develop strabismus” using genetics
Faced with these data, the authors introduced the chromosomal variants into pluripotent stem cells. Their goal ? Differentiate these cells into neurons and look for changes in neuronal structure and function, as well as gene expression to understand how variants contribute to strabismus.
In their conclusions, they specify that these results are not yet sufficient to contribute to the creation of specific treatments for strabismus. However, “The advantage of genetics is that we may one day be able to identify people at risk before they develop strabismus. We could even possibly prevent it, if we knew who to target and if we could give them treatment “.
