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S. Shaaban, T. Matsuo, T. Furuse, S. Hasebe, H. Ohtsuki; Are Refractive Errors and Comitant Strabismus Linked to the Same Susceptibility Loci?. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2313.
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Population, family and twins studies have suggested the heritability of refractive errors and comitant strabismus. A correlation between refraction and strabismus has been often observed. Hyperopia is a well-known risk factor for accommodative esotropia. Whether refraction is an inherited aspect of the strabismic syndrome remains a question to be answered. Our aim was to investigate if chromosomal regions showing linkage to refractive errors were also linked to comitant strabismus.
Fifty-five Japanese families with comitant strabismus (esotropia and/or exotropia) were included. Probands and available family members were clinically examined and DNA was isolated from samples of venous blood. Four hundred microsatellite regions were amplified by PCR. Using an ABI310 Genetic AnalyzerTM, genotypes were determined. A genome-wide linkage analysis was performed using GENEHUNTER-MODSCORE version 3.0 and results were presented as MOD scores (MOD), non-parametric linkage scores (NPL) and their corresponding P-values. A subgroup of families whose affected probands manifested both comitant esotropia and hyperopia (21 families) was analyzed separately. We screened 15 chromosomal regions previously reported to show linkage to refractive errors and searched for whether evidence of linkage to comitant strabismus could also be obtained at these regions. Any evidence of linkage to comitant strabismus found along an area of 20 cM on either side of the refractive error-implicated loci was considered a positive result.
Six chromosomal regions that were reported to show suggestive or significant evidence of linkage to refractive errors, also showed evidence of linkage to comitant strabismus in the analysis of the 55 families. Evidence of linkage was observed at 2p21 (MOD= 2.87, NPL=2.33, P= 0.005), 4q28.3 (MOD=4.17, NPL=2.68, P=0.001),7p (MOD=2.29, NPL=2.32,P=0.005), 9p24.1 (MOD=2.2, NPL=2.00,P=0.01), 10p11.22 (MOD=2.02, NPL=2.08, P=0.01) and 11q23-24 (MOD=2.69, NPL=1.87, P=0.02).In the analysis of the 21 families with esotropia and hyperopia, 3 regions were found to show evidence of linkage to both comitant esotropia and refractive errors. These loci were located on chromosomes 1p36 (MOD=2.61, NPL=2.4, P=2.1, P=0.005), 7p (MOD=2.13, NPL= 2.16, P= 0.005) and 10p11.22 (MOD=2.42, NPL=2.17, P=0.004).
Our results revealed that comitant strabismus and refractive errors showed evidence of linkage to the same susceptibility loci at several chromosomes. Genetic interaction could be one aspect of the complex inheritance mechanisms underlying both traits.
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