Certain Genetic Duplications May Cause Increased Exotropia and Esotropia Risk

Three genetic duplications seen in patients with exotropia also appear to occur at the same prevalence rates in those with esotropia, increasing the risk of developing either condition.

Study Design

Investigators at Boston Children’s Hospital conducted a cross-sectional study between 2005 and 2023, using DNA information collected from 234 participants (mean age 19.5 years; range 1.0−77.8 years) enrolled in an ongoing strabismus genetics study, to determine if the genetic risk factors for exotropia are also risk factors for esotropia. Patients with constant or intermittent exotropia and a history of strabismus surgery for exotropia were recruited, as well as patients with and without a family history of strabismus.

Outcomes

Genetic duplication in chromosome 2 (2p11.2) was present in 1.7% of patients with exotropia and 1.4% of patients with esotropia. Genetic duplication in chromosome 4 (4p15.2) was present in 3.0% of patients with exotropia and 1.7% of patients with esotropia. Genetic duplication in chromosome 10 (10q11.22) was present in 6.0% of patients with exotropia and 4.0% of patients with esotropia. In total, 10% of patients had ≥1 of these genetic duplications, and this group had larger angle deviation measurements, were more likely to have constant vs intermittent exotropia, and had higher rates of surgery for exotropia than patients who did not have these duplications.

Limitations

While the authors identified 3 specific duplications in chromosomes 2, 4, and 10 in patients with exotropia, the study design does not allow them to assert that these duplications actually cause exotropia. These genetic duplications are quite rare and there may have been recruiting biases, with patients with a family history of strabismus perhaps being more likely to participate. The majority of patients self-identified as non-Hispanic White, and the wide age range of the patients was also a limitation, as the authors did not have data about the age of strabismus onset in this population.

Clinical Significance

For pediatric ophthalmologists who care for patients of all ages with strabismus, this study does not change how we manage and treat our patients. However, the results allow clinicians to tell our patients with strabismus that 3 genetic duplications have been identified in a large cohort and that these specific genetic duplications may be risk factors for both types of horizontal strabismus. Additional genetic strabismus studies are needed in a larger multiracial cohort that includes the age of strabismus onset in its demographic information.

Financial Disclosures: Dr. Jennifer Galvin discloses no financial relationships.