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Janet P. Lee, Seanna R. Grob, Ling Zhao, Mahmoud El-Sahn, Guy Hughes, Louise Mao, Jin Zhu, Xinran Wei, David Granet, Kang Zhang; Myotonia Congenita With Strabismus In A Large Family With Mutation In SCN4A Gene. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1558.
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To determine the genetic basis of myotonia congenita (MC) and strabismus in four generations of individuals in a large family.
7 patients making up four generations of a family with non-dystrophic myotonia (NDM) and strabismus were recruited. All patients had standard ophthalmic exam, including best-corrected visual acuity, refraction, and ocular motility measurements. CLCN1 and SCN4A genes were sequenced and analyzed for mutations.
5 out of 7 patients in the family were diagnosed with MC by clinical history and electromyography. Ophthalmic history and exam revealed eyelid myotonia and strabismus. Age of onset with strabismus was between 3-6 year old. Sequencing results revealed a c. 1333G>A; p. Val445Met mutation in the SCN4A gene in all affected patients.
There are few reports describing eyelid myotonia and strabismus in patients diagnosed with NDM. We found sodium channel myotonia in a family with significant ocular involvement. Future studies will confirm the association between sodium channel mytonia and ocular manifestations of the disease and may lead to genetic therapy for treatment of such patients.
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