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Jieun Kwak, Asadolah Movahedan, Peyman Tadjvidi, Parisa Aref, Irene H. Maumenee; Mendelian Inheritance of Strabismus in a Rural Community of Northern Iran. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6359.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the subtypes and etiology of strabismus in a geographically isolated community with a long history of squint among its inhabitants.
We learned about a high frequency of strabismus in a small community located in the Alborz Mountains, a range in northern Iran stretching from the northwest borders with Armenia to the southern end of the Caspian Sea, ending in the east at the borders of Turkmenistan. In view of this high frequency, we evaluated the types of strabismus occurring in the community and its etiology. An epidemiologic study was performed to analyze the prevalence and potential causes of strabismus in this geographically isolated and highly inbred community. Strabismus was defined as any ocular misalignment (horizontal, vertical, torsional or combined). Participants were examined over a period of three months from October to December 2009. The family history, birth history and past medical, ocular and surgical history were also obtained from each subject.
We evaluated 243 out of 324 (75%) of the permanent residents of the village and diagnosed 36 cases of strabismus; of the affected subjects, two with mental retardation and one with poor visual acuities of unknown etiology were excluded from further analysis. The prevalence of strabismus in the screened population was 14.8% (36/243). The sex ratio was 1.1 (19 males,17 females). In all subjects a deviation was noted at birth by history. All cases were diagnosed with comitant strabismus in examination. Exotropia was observed in 88% (29/33) followed by esotropia in 12% (4/33). The examined population had no accompanying diseases aside from common conditions such as hypertension and DM type II. Pedigrees were most compatible with an autosomal recessive inheritance of exotropia. The gene frequency (q) was estimated to be q=0.36 with a heterozygous frequency (2pq) of 0.45.
The prevalence of exotropia in the studied community was considerably higher than the observed rate in the general population. The pedigree analysis suggests an autosomal recessive mode of inheritance. Given the geographic isolation of the village, a founder effect followed by genetic drift likely led to the high prevalence of strabismus. Genetic studies in search of the causative gene are ongoing.
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