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S.K. Nath, R. Singh, R. Meda, R.M. Memon, R. Uppala, R. Uppala; Congenital Nystagmus: Exclusion of Linkage With Markers on Chromosomes 6p12, 7p11, and 13q31–q33 in a Large Indian Family . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2507.
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Congenital nystagmus (NYS) is characterized by bilateral, and uncontrollable, involuntary movement of the eyes. Its incidence is about 1 in 1500 live births. It is one of the most common neuro ophthamalological disorders among live births, and also reduces visual acuity. The genes responsible for X–linked form of the disease on Xp11.4–p11.3 (NYS1) and Xq26–q27 (Am. J. Hum. Genet. 64:1141–6, 1999; Am. J. Hum. Genet. 64:600–7, 1999; Ophthalmic Genet. 22:241–8, 2001; Hum Genet.116:128–31, 2005); and an autosomal dominant form on 6p12 (NYS2) (Genomics 33:523–6, 1996) have been mapped, but no causal gene is yet identified. In addition, two other loci have been proposed; one on 7p11.2 (NYS3) (J. Med. Genet 30:526–8, 1993) and another on 13q31–q33 (NYS4) (J. Med. Genet. 40:37–41, 2003). We have studied an extremely large eleven–generation Indian pedigree with an isolated non–syndromic NYS in which the anomaly appears to be segregating as an autosomal dominant trait with reduced penetrance. The family is highly consanguineous and over 15 consanguineous marriages observed this pedigree. The pedigree consists of 444 individuals with 62 affecteds (34 males and 28 females). The onset of NYS is during early infancy, and the age distribution of the affected individuals ranges from 6–90 years. Clinical examinations were performed on twenty–five selected affected individuals. These included color vision testing, transillumination defects of the iris and eye movement recordings. All the examined individuals showed asymmetric pendular eye movements with unidirectional jerky NYS. Head nodding was observed in 10 out of the 25 affected individuals examined. No other associated anomalies, such as decreased vision, strabismus, color blindness, ocular albinism or congenital stationary night blindness were observed. Chromosomal analysis was done on five affected individuals and a balanced translocation was excluded. Linkage studies with markers closely linked to NYS2, NYS3 and NYS4 did not show the involvement of the above regions in this family. This also supports that there is genetic heterogeneity in NYS since more than one linked loci have been identified. We are planning to perform a genome wide linkage analysis to identify the responsible locus.
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