In the field of special education, dyslexia is classified as a common learning disability but its very nature has never been studied until late in the 20th century. Prior to extensive research studies about dyslexia, this condition was just a last resort description of a child who could not manage to read despite the absence of obvious causes such as poor eyesight and poor hearing. A child, who appears to have average or sufficient intelligence but could not read or spell correctly is considered dyslexic. Additional researches revealed that dyslexia has a neurological basis. The National Institutes of Health described it as an inherited condition that is linked to the 6th chromosome. Today, after further studies of the brain, dyslexia is not just hereditary. It is the absence of phonemic awareness. A phoneme is the smallest unit of speech or spoken word. Without the ability to understand, distinguish and manipulate phonemes, a child could not link sounds to letters. The absence of phoneme awareness is the major and root characteristic of dyslexia. With this knowledge about dyslexia, there are now three types of dyslexia. These are trauma dyslexia, deep dyslexia, and developmental dyslexia.
Trauma dyslexia, which is also referred to as acquired dyslexia, is the rarest type of this learning disability. It is not inherited at all. It is caused by a brain injury or a serious illness that has adverse effects on the functions of the brain. The child, before suffering from trauma dyslexia, had the ability to read and comprehend written words. But due to a brain disease or an infarction to parts of the posterior cerebral artery, the ability to make sense of words disappears. In younger children, the frequent cause of trauma dyslexia is called "glue ear." It is a conductive hearing loss that is due to flu, cold, or other ear infections. The loss of the ability to hear spoken words prevents the child from acquiring phonemic awareness.
Deep dyslexia, which is also known as primary dyslexia, is the hereditary type of this condition. It runs in families and the identified culprits are in chromosomes 6 and 15. The affected hemisphere of the brain is the left, resulting in what scientists described as an "unusual wiring." There seems to be a disorganized architecture of the brain with neurons appearing in areas where they don’t usually go. In a deep of primary dyslexia, the left hemisphere could not be utilized efficiently, forcing the child to compensate with the right brain. This is why some of signs of this type of dyslexia include left-handedness, above average athletic and artistic abilities, and intuitive interpersonal skills. Unfortunately, the accompanying dyslexia symptoms include allergies, recurrence of intestinal problems, and various immune disorders.
Developmental dyslexia, which is also called as secondary dyslexia, occurs during the developmental stages of the fetus. There were problems in the development of the brain leading to impaired neurological abilities in word recognition and spelling. The good news about this type of dyslexia is that the severity of the condition decreases as the child grows older. The child may continue to struggle with the dyslexia symptoms throughout his or her puberty but may perform well in college if there were early interventions, especially in phonics instructions.