Increase in blood derived mitochondrial DNA copy number in strabismus patients

Background: Abnormalities in mitochondrial energy homeostasis can lead to various disorders, including ocular motility aberrations. Previous studies have suggested the involvement of mitochondrial aberrations in strabismus etiology. We compared the blood-derived mitochondrial DNA (mtDNA) copy number from comitant strabismus patients with that from age-matched controls, and also compared expression of mitochondrial biogenesis genes in a separate set of extraocular muscle samples from strabismic and control subjects.

Methods: Blood samples from 93 strabismic (39 esotropic, 54 exotropic) and 93 control subjects were analyzed for mtDNA copy number through quantitative polymerase chain reaction. We also examined the expression of 6 genes involved in mitochondrial biogenesis in cDNA obtained from extraocular muscles of a separate group of 26 strabismus patients and 4 healthy controls.

Results: The mtDNA content was significantly higher in strabismus patients as compared to the control group, both overall (fold change, 1.39; Z = -2.43 [P = 0.01]) and in strabismus subgroups (esotropia: fold change,1.42; Z = 2.59 [P = 0.0096]; exotropia: fold change, 1.41, Z = 3.35 [P = 0.00078]). No significant difference was observed in the expression of the examined biogenesis genes between strabismus and control groups.

Conclusions: Our results suggest an association between mtDNA copy number and strabismus; however, further studies are required to elucidate the significance of altered mtDNA in strabismus and its possible significance with regard to the etiology of strabismus.