Major cause of blindness inherited

Age-related macular degeneration, a leading cause of blindness in older adults, is greatly influenced by a person's genes.Based on perhaps the largest twin study of age-related macular degeneration to date, researchers from the Harvard Medical School, USA, quantified substantial genetic influences by studying 840 people with an identical twin with macular degeneration. The workers found that identical twins were twice as likely than fraternal twins with the disease to have the same degree of blindness. Among identical twins with the disease, 55 percent had the same severity of the disease, compared with 25 percent of the fraternal twins. Environmental factors, such as whether the victim smoked or was obese, contributed to the severity in 19 percent to 37 percent of cases.Identical twins are monozygotic, coming from the same egg that splits after fertilization and sharing the same genes. Fraternal twins are dizygotic, meaning two eggs were fertilized simultaneously.The researchers reported the discovery of a variation in a single gene that could be responsible for half of all cases of age-related macular degeneration. The gene is involved in a component of the immune system that regulates inflammation.Macular degeneration erodes the center of the field of vision due to the accumulation of waste deposits in the macula, the center of the retina that is packed with cones that help in seeing color, detecting motion and making out fine detail. 

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