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Linda K McLoon, Christy Willoughby, Jill S Anderson, Erick D Bothun; Examination of Extraocular Muscles and Their Innervation from Subjects with Infantile Nystagmus Syndrome and Albinism. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4548.
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© ARVO (1962-2015); The Authors (2016-present)
Infantile nystagmus syndrome (INS) is an eye motility disorder characterized by involuntary bilateral oscillatory eye movements. INS is often associated with reduced visual acuity secondary to structural abnormalities in the afferent visual pathways. Our previous work suggested that the “idiopathic” form of INS may be related to dysregulation of innervation. The only gene thus far identified with INS, FRMD7, is associated with altered innervation developmentally. INS is associated with optic nerve hypoplasia and albinism, which are known to have altered CNS projections from the retina. Our working hypothesis is that the extraocular muscles (EOM) from INS patients with albinism will have muscular and innervational adaptations that may provide insight into possible mechanisms that cause INS.
We have examined EOM specimens removed as part of the normal surgical treatment of patients with INS and albinism. They were examined for innervational and neuromuscular junction density, and neuromuscular junction morphology. They were compared to aged matched control EOM. All studies were approved by the IRB at the University of Minnesota.
The EOM from the subjects with INS and albinism showed a number of features suggestive of innervational dysregulation. The myofibers were extremely heterogeneous in cross-sectional area, with many centrally located myonuclei, a classic sign of denervation/reinnervation. Both neuromuscular junction and nerve density were significantly decreased in the EOM from the INS albino subjects compared to age-matched controls. In addition, the neuromuscular junctions were smaller and thinner than in normal EOM.
It appears that the EOM in patients with INS and albinism have changes suggestive of a dysinnervation syndrome, including reduced innervational density and reduced neuromuscular junctions numbers and size. These results suggest potential new approaches that might be used to alleviate the abnormal oscillatory movements associated with INS.
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