This is now a rare cause of mental retardation since the introduction of the measles vaccine. Rubella virus belongs to the Togaviridae family of viruses. In children this virus usually causes a non-symptomatic infection (German measles) and in adults may cause a prodrome of low-grade fever, headache, malaise, mild coryza, and conjunctivitis. Maternal infection during the first trimester is usually transmitted to the fetus leading to infection, often causing miscarriages and stillbirths; however, up to 20 per cent survive to develop congenital rubella syndrome. Infection beyond 16 weeks gestation is far less likely to cause congenital rubella syndrome. Around 80 per cent of the affected subjects have ocular disorders such as cataracts and microphthalmia leading to poor visual acuity. About 60 per cent have sensorineural hearing deficit, psychomotor retardation, and cardiac abnormalities, and about 40 per cent have mental retardation. This syndrome is also associated with diabetes mellitus and thyroid disease. (61
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