Lesser Known Disorders
Each issue of this series contains at least three lesser known disorders. Some of these disorders may contain subtypes which will also be presented. You will also notice that each disorder has a code. These codes represent the coding system for all disabilities and disorders listed in the Educator’s Diagnostic Manual(EDM) Wiley Publications.
LD 9.03-Tactile defensive type
Disability Category – Learning Disabilities
The tactile system is our sense of touch through different sensory receptors in our skin. It is through the tactile system that we first receive information about the world when we come out from the womb environment. The ability to process tactile information effectively allows us to feel safe and form bonding with those who love us. It contributes to our social and emotional development.
One important role of our tactile system is its protective function that alerts us when something is unpleasant or dangerous. For some children, this function of the tactile system is not working normally. They may perceive most touch sensations to be uncomfortable or scary and react with a flight-or-flight response. We call this condition tactile defensiveness, which was first identified by Dr A.J. Ayres, an American Occupation Therapist around the 1960s (Chu, 2004).
Theoretically, when the tactile system is immature and working improperly, abnormal neural signals are sent to the cortex in the brain which can interfere with other brain processes. This, in turn, causes the brain to be overly stimulated and may lead to excessive brain activity, which can neither be turned off nor organized. This type of over-stimulation in the brain can make it difficult for an individual to organize one’s behavior and concentrate and may lead to a negative emotional response to touch sensations Hatch-Rasmussen, 2001).
If a child suffers from dysfunction in the tactile system, he may experience light touch or a gentle hug as intense or aversive, he may find certain kinds of fabrics or clothing irritating, may refuse to eat foods of a particular texture, and may avoid touching or handling certain kinds of objects. We say that a child is “tactile defensive” when he or she is extremely sensitive to light touch.
Prader-Willi syndrome
Disability Category – Mental Retardation
PWS is a complex genetic disorder that typically causes low muscle tone, short stature, incomplete sexual development, cognitive disabilities, problem behaviors, and a chronic feeling of hunger that can lead to excessive eating and life-threatening obesity.
Prader-Willi syndrome affects an estimated 1 in 10,000 to 22,000 people.
This condition is due to the effects of the loss of active genes in a specific region of chromosome 15. People normally have two copies of this chromosome in each cell, one copy from each parent. Some genes on this chromosome, however, are only active when they are inherited from a person’s father (the paternal copies). Prader-Willi syndrome occurs when the region of paternal chromosome 15 containing these genes is missing.
Researchers are not yet certain which genes on chromosome 15 are responsible for Prader-Willi syndrome or why a lack of those genes leads to the characteristic features of the condition. They have determined, however, that a loss of the OCA2 gene is responsible for the unusually fair skin and light-colored hair in some affected individuals.
Most cases of Prader-Willi syndrome (about 70 percent) occur when a segment of paternal chromosome 15 is deleted. In about 25 percent of cases, a person with Prader-Willi syndrome has two copies of chromosome 15 inherited from his or her mother (maternal copies) instead of one copy from each parent. This phenomenon is called maternal uniparental disomy. Rarely, Prader-Willi syndrome can also be due to the effects of a chromosomal rearrangement called a translocation, or by a mutation or other change that abnormally inactivates genes on paternal chromosome 15. Each of these genetic changes results in a loss of gene function in a critical region of chromosome 15.
Most cases of Prader-Willi syndrome are not inherited, particularly those due to the effects of a deletion in paternal chromosome 15 or by maternal uniparental disomy. These genetic changes occur as random events during the formation of reproductive cells or in early fetal development. Affected people typically have no history of the disorder in their family.
Rarely, a genetic change responsible for Prader-Willi syndrome can be inherited. For example, it is possible for a mutation that abnormally inactivates genes on paternal chromosome 15 to be passed from one generation to the next (National Institute of Health, 2004).
AU 5.00-Hyperlexia
Disability Category – Autism
Definition
A type of syndrome often associated with autistic features characterized by above normal ability to read coupled with a below normal ability to understand spoken language (American Hyperlexia Association, 2005).
Diagnostic Symptoms
Hyperlexia is a syndrome with the following three main characteristics (Autism Support Network, 2002):
1. Early precocious and/or intense fascination with letters or numbers
2. Delays in verbal language
3. Social skills deficits
Examples of the above include (American Hyperlexia Association, 2005):
- Learn expressive language in a peculiar way, echo or memorize the sentence structure without understanding the meaning (echolalia), reverse pronouns
- Listen selectively, appear to be deaf
- Normal development until 18–24 months, then regression
- Rarely initiates conversations
- Self-stimulatory behavior
- Significant difficulty in understanding verbal language
- Specific, unusual fears
- Strong auditory and visual memory
- Think in concrete and literal terms, difficulty with abstract concepts
Further KeyPoints
Hyperlexia has characteristics similar to autism, behavior disorder, language disorder, emotional disorder, Attention Deficit Disorder, hearing impairment, giftedness or, paradoxically, mental retardation.
To develop effective teaching strategies and more typical childhood development, it is important to differentiate Hyperlexia from other disorders. Thorough psychological evaluation by a psychologist who is familiar with the syndrome of Hyperlexia is a crucial first step. Hearing, neurological, psychiatric, blood chemistry, speech and language and genetic evaluations can be performed to rule out other disorders but are not needed to identify Hyperlexia (Kay, 2004).
According to the American Hyperlexia Association (2005), “Hyperlexia’s place on or outside of the autistic spectrum is a matter of much debate. Be that as it may, hyperlexia is a trait commonly seen in autistic spectrum disorders. Autistics with hyperlexia have a unique learning style and a better prognosis than those without this reading skill. Hyperlexia is often written off as a “meaningless splinter skill” but it is much more than that even if comprehension lags because reading can be a very useful tool for learning other skills and can be the doorway to language in general” (p.1).
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