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Biology 202, Spring 2005 Second Web Papers On Serendip

A Lack of Inherent Motor Symphonies in Rett Syndrome Sufferers: Is it plausible?

Leslie Bentz

As we discussed the idea of inherent motor symphonies or inherent patterns of activity across motor neurons, I questioned what the exception to the rule might be. Surely not everyone could automatically be so adept as to possess such skills from birth. There had to be an example in which the idea of inherent motor skills, or motor skills that simply needed refining was not such a plausible notion. Surely there had to be some infants who were not inherently born with all the needed internal wiring to understand the feat of walking before they even began to crawl. This idea of innateness in regards to motor skills seemed to be a particularly riveting and a questionable assumption that we had taken to be truth. Since discussing the formations of neurons and each person's variability in this setup, it seemed particularly probable that not everyone is equipped with inherent aptitudes towards performing motor skills. This search for a contradiction led me to Rett Syndrome (RS) with its symptoms of apraxia (inability to perform motor functions) and sudden degeneration that afflict its sufferers.

Initially, RS is very indiscernible in patients and it is only in hindsight that many parents remember the first signs of their infant's health problems. Typically signs of the disorder present themselves early in infancy with the first noticeable indicator being a deceleration of head growth between two and four months of age ((2)). Followed by "a period of developmental stagnation" which quickly, or not so quickly in some cases, develops into regression, these children begin to lose purposeful motor skills. A child's nervous system is not the only affected body system; problems with breathing and digestion are also prevalent ((2)).

The cause of this disorder results from a genetic mutation. RS is a disorder that appears solely on X chromosomes. Thus women are the primary carriers of the mutated gene and are the ones most afflicted by its mutation. Since women are equipped with two X chromosome, one of which randomly is inactivated, patients who possess one mutated MECP2 gene can survive. Although possible for males to posses this altered gene, there have been very few documented cases. It is believed that most male fetuses that embody this genetic mutation die while still developing in the womb ((2)).

"The symptoms and severity of RS may depend on both the percentage of activated defective genes and the type of mutation" ((2)). Once symptoms become visible, genetic testing can be used as a means to diagnose this disorder. This form of testing is the primary means for making an accurate diagnosis but strangely, "as many as 20% of females meeting the full clinical criteria for RS may have no identified [gene] mutation" ((2)).

This gene anomaly leads to a number of affected neurological processes. Firstly, the disruption that this mutation encourages influences crucial parts of nervous system development beyond the initial stages ((8)). This primarily has an effect on the proper development of neural pathways and synapses thus disrupting the genetic processes responsible for controlling the specificity of neuronal connections during the early postnatal period ((4)). These genetic abnormalities create chemical discrepancies in the brain. Due to these chemical idiosyncrasies, excitatory synapses are being overworked, which becomes an essential component in understanding the outward symptoms and seizures that RS patients experience.

These problems involve glutamate, the major excitatory neurotransmitter in the brain. Most neurons possess receptors that respond to glutamate. "Glutamate synapses mediate primary senses such as hearing and vision, activate motor acts such as speaking or walking, and play essential roles in learning and memory" ((3)). Thus glutamate stimulates activity in the brain. Levels of glutamate have been found to be exceptionally high in patients between the ages of 2-8 but are well below average in older women with RS ((3)). It is this drop in glutamate that could account for the stagnate or regressive pattern of development that is witnessed in aspects of behavior and intelligence of RS patients.

More specifically in regards to how motor skills are affected, it is essential to look at how RS has been categorized into four stages of motor skill disorder. The first stage involving developmental arrest is typically noted between the ages of 6-18 months. Babies not stricken with RS typically exhibit attempts at walking during this period but for most RS patients this stage of development is never reached. Next a period of rapid deterioration ensues which is characterized by loss of purposeful hand use as well as seizures. This stage can persist until a patient is ten years old. After the age of ten these women classically do not undergo further deterioration but increasing motor problems do persist. Ultimately, "most patients with RS survive into the fifth or sixth decade of life" but continue to experience severe motor skill impairments ((2)).

Although these are the physical outcomes from internal dysfunctions, it is important to note why this disorder is considered neurological. In classic cases "RS is associated with a significant decrease in cerebral cortex size, cerebella atrophy, and a brain weight that is approximately 70-90% of normal" ((2)). Since expansion of the brain ceases shortly after postnatal development it never reaches full maturity. It is this underdevelopment that is to blame for the permanent motor skill inadequacies. Abnormal motor skills are witnessed in a number of physical outputs. Such manifestations can include, but are not limited to seizures, tensed body postures, and loss of willful hand use. Although devastating, the most intriguing problem one may suffer is the inability to walk.

Although not found in all diagnosed cases, some sufferers have "permanent flexion or extension of affected joints in fixed postures" which is similar to the deterioration that stroke victims fall prey to ((8)). In the case of stroke victims it is the I-function, or will of the person, that is no longer responding. Motor neurons are still reacting which leaves the appendage stiff and unresponsive but the person can not purposefully change the position. I question whether it is a similar phenomenon presenting itself in RS patients. There is no evidence that the nervous system is affected beyond certain aspects of the brain. So then what has limited their motor skills?

As symptoms of RS progress, patients find it increasingly difficult to walk and most are ultimately immobilized. Instances have even presented themselves in which patients never began walking. It was these instances which prompted me specifically to question the notion of inherent motor skills. I am now rather skeptical about the idea of innate motor symphonies which are in place at birth. If it is true that infants are born with the inherent knowledge of how to walk and manipulate their appendages; then it is essential to know the exact point during gestation in which this knowledge or process becomes active. It conceptually seems quite probable that this activation of inherent motor symphonies does not occur until late in the gestation period, thus maybe it is possible to be born without such structures in place.

These women are not paralyzed in the traditional sense. The sensory and motor neurons throughout their bodies appear intact, so why is their mobility impaired? Could simply a lack of will or agency account for this physical shortcoming? Could this be a case in which mind over matter can be attributed? Does this prove that the I-function does in fact play a vital role in central pattern generation? If their central pattern generators have ceased reacting or have never possessed this quality from the start; thus maybe the idea of an inherent motor symphony is not plausible for sufferers of this disorder.

Ultimately there are exceptions to every rule and at the time we discussed inherent motor scores we did not discuss this possibility. We took it as truth and possibly "true reality" but maybe our perceptions and understandings of the working of motor symphonies are not complete. I was forced to reevaluate my perceptions of the world and the controlling of behaviors after thinking about the innateness of motor skills at birth. If motor skills are in fact not intrinsically universal for everyone then a huge reevaluation of how behaviors are learned and perceived to manifest themselves is in store. It is purely my own controversial speculation as to whether or not motor symphonies have to be inherent in everyone at birth but it appears to be plausible that at least in the case of RS patients that our hold on truth might not be such a tight grasp.


1) Similar Disabilities information
2) Pervasive Developmental Disorder: Rett Syndrome , Joseph H. Schneider, MD
3) Neurobiology of Rett Syndrome , Michael V. Johnston, MD; Brendan Mullaney, BA; Mary E. Blue, PhD
4) Neurobiology of Rett Syndrome: a genetic disorder of synapse development , Michael V. Johnston, Ok-Hee-Jeon, Jonathan Pevsner, Mary E. Blue, SakkuBai Naidu
5) Child and Brain: The Stages of Development , Gerald Gabriel
6) Syndrome Fact Sheet , National Institute of Neurological Disorders and Stroke
7) Our Rett Syndrome Web Site
8) Rett Syndrome Information for Patients and Caregivers , Joy B. Leffler, NASW, AMIA
9) Rett Syndrome , Huda Y Zoghbi, MD

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