Physical and sensory disorders and disabilities

This chapter outlines some of the major physical and sensory disorders and disabilities which may give rise to special educational needs. This includes organic disorders which primarily affect intellectual development and mobility; hearing and visual impairment; and speech, language and communication disorders. The most commonly occurring of the chromosome disorders is Down's syndrome or mongolism, which affects approximately one child in 700. The child with Down's syndrome typically, has an extra chromosome in the 21st pair making a total of 47, although other abnormal arrangements in the chromosomes have also been identified. There are a number of rare disorders resulting in severe mental handicap which are genetically transmitted. The largest group are inherited metabolic or endocrine disorders such as phenylketonuria, homocystinuria, galactosaemia and cretinism. Another group of rare inherited disorders affects the bone formation of the skull. These defects often lead to, or are accompanied by, severe mental retardation.