Reading disorder was first recognized in the late nineteenth century, when it was called pure word blindness, then developmental alexia. Starting in the 1960s, educators commonly referred to reading disorder as dyslexia, from the Greek word dys, meaning poor or inadequate, and the word lexismeaning words or language. Despite the long history of reading disorder, its cause is not known.
Learning to read is a complex task. It requires coordination of the eye muscles to follow a line of print, spatial orientation to interpret letters and words, visual memory to retain the meaning of letters and sight words, sequencing ability, a grasp of sentence structure and grammar, and the ability to categorize and analyze. In addition, the brainmust integrate visual cues with memory and associate them with specific sounds. The sounds must then be associated with specific meanings. For comprehension, the meanings must be retained while a sentence or passage is read. Reading disorder occurs when any of these processes are disrupted. For that reason, the roots of reading disorder have proved difficult to isolate, and may be different in different individuals.
Despite the complexity of reading disorder, researchers have found that the condition is at least partially inherited. In 1999, the Centre for Reading Research in Norway studied a large family with reading problems. By evaluating the reading and writing abilities of about 80 family members across four generations, the researchers were able to pinpoint mutations in specific genes that are associated with reading and writing deficits.
It appears that reading disorder may also have causes other than genetic inheritance, as about half the people with this learning disability do not come from families with a history of the problem. Many theories suggest that functional problems in specific areas of the brain underlie reading disorder. Given the complicated demands on the human nervous system involved in reading, it is entirely possible that there are several different problems in brain function related to difficulty in learning to read. What is known is that 90% of children diagnosed with reading disorder have other language deficits. Still other research suggests a possible link with a subtle visual problem that affects the speed with which affected people can read.
Tish Davidson A.M., The Gale Group Inc., Gale, Detroit,