Increase in blood derived mitochondrial DNA copy number in strabismus patients

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.

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.

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.

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.