The Link Between Down Syndrome and Alzheimer's Disease

Biology 202
2002 First Paper
On Serendip

The Link Between Down Syndrome and Alzheimer's Disease

Aly Dymkowski

The individuals with Disabilities Education Act states that "all children with disabilities, including mental retardation, be educated to the maximum extent appropriate with students who are not disabled" (2). In an ideal world, society would have no problem following this decree, but the world is less than perfect and, therefore, stigmas are unfortunately attached to those suffering from mental disabilities, especially the mentally retarded. One has to question whether this group of people deserves these stigmas. Having grown up with two severely retarded cousins and, for that matter, a great uncle suffering from Alzheimer's Disease, I often wondered as to what was happening within their brains. It was evident that they were unable to respond to me in a normal fashion, but I challenged whether this was just a veneer. Being a spiritual person and believing the mind to be akin to 'the soul', I always felt it must be separate from the brain. A part of me hoped that their minds were still cognizant even though their brain appeared to have a different physiology and they seemed to be unable to respond to me in a normal fashion. However, upon researching the link present between Down Syndrome and Alzheimer's Disease, I began to question whether my previous beliefs were indeed true. I think the questioning of this raises ethical issues about how we treat the mentally disabled and gives quite an argument for the brain = behavior debate.

As more and more adults live longer, age-associated mental disease is becoming more and more of a concern. Present estimations state that soon nearly 10 million Americans will suffer from the disabling disease called Alzheimer's. Alzheimer's sufferers endure the progressive deterioration of cognitive, physical, and adaptive skills, and have a distinctive model of neuropathology (11). The fact that individuals displaying the same symptoms have similar abnormalities in their brains gives supporting evidence to the brain = behavior argument. In further support, studies have suggested that mentally retarded adults have the same risk as other adults of developing Alzheimer's disease, which affects roughly 6% of adults over 65 in the general population. However, adults with Down Syndrome have a much higher rate of developing the disease. 25% of adults with Down Syndrome develop the disease by age 40, and the rate sky-rockets to 65% after age 60. Upon autopsy at death, nearly all adults that suffered from Down Syndrome show brain patterns analogous with those of Alzheimer's (9) . If the brain is responsible for the behaviors demonstrated by the sufferers of both Down Syndrome and Alzheimer's, then one has to question what the link is. What makes the transition from one to the other more frequent than in the general population and why are the mentally retarded not afflicted by Alzheimer's as often as those with Down Syndrome?

Down Syndrome is the most common genetic form of mental retardation and occurs in about 1 out of every 800 births. It has distinctive characteristics that allow it to be easily distinguished from other forms of mental retardation (3). Factors such as maternal age, hormonal abnormalities, x-rays, viral infection, immunologic problems, and genetic predisposition can cause the improper cell-division during meiosis responsible for the syndrome. As a result of this, individuals with Down Syndrome have an extra trisomic chromosome 21 (8). Like Alzheimer's patients, the Down Syndrome brain is different than that of the general population. Down Syndrome's patients have a hindered ability to perform tasks involving cognitation and suffer from other physiological and mental differences (3). The behaviors displayed by individuals with Down Syndrome are similar to those displayed by individuals with Alzheimer's. However, they are not the same and the two diseases can be distinguished from one another. One of the main differences between the two mental diseases is that people are born with Down Syndrome, unlike Alzheimer's, which sets in late in life. One has to remember that even though a person with Down Syndrome has limitations in intellectual functioning, he or she can often function quite normally in the community and can utilize daily living skills, which often disappear with the onset of Alzheimer's (1).

If Down Syndrome patients already display problems with cognitation, then one must wonder as to how the transition from Down Syndrome to Alzheimer's can be witnessed. The problem of Alzheimer's for those with Down Syndrome is especially disconcerting because the progression from the onset of the disease to death takes less time than in the general population. The disease can run its course in 2-8 years depending on the individual and is not always apparent in the beginning. Because the brain is already impaired, memory loss is not always noted at first. With the onset of Alzheimer's, the retarded individual's behaviors often change. These changes may include: the development of seizures, the changing of personality, the occurrence of long periods of inactivity or apathy, the development of hyperactive reflexes, the loss of activity and utilization of daily living skills, the visual retention deficits, the loss of speech, the onset of disorientation, the increasing of stereotyped behavior, and the appearance of abnormal neurological signs (9).

Alzheimer's Disease is identified by senile plaques, made of amyloid peptides, which are derivatives of a large precursor protein, encoded by genes on chromosome 21, and neurofibrillary tangles in the brain. Due to the presence of three copies of chromosome 21 in Down Syndrome patients, scientists are investigating whether the overexpression of the precursor protein may explain the increased occurrence of Alzheimer's Disease in those afflicted with Trisomy 21 (8). It has been demonstrated by a rare genetic defect that mutations of the amyloid percurson protein gene lead to the early development of Alzheimer's Disease. A number of genes found on chromosome 21 may also be responsible for this as well. A gene located on Chromosome 14, coding for the S182 protein, was discovered in 1995 and may be a cause of early onset Alzheimer's Disease. Other genes were discovered recently, including a gene on chromosome 1 that shares similarities with the S182 gene. A protein called APOE4 has been found to be present in almost half of all Alzheimer's cases. It is coded by a gene on chromosome 19 and binds to the amyloid, (the substance present in the Alzheimer brain) (12). A mouse model for partial trisomy 16 is now being used to study the onset of Alzheimer's Disease in those with Down Syndrome because this segment is homologous with chromosome 21 in humans (8). If the Alzheimer's is caused by the presence of this third copy, then there is no explanation as to why Alzheimer's occurs in the general population as well. One of the greatest arguments found for the link between the two diseases comes from Huntington Potter, associate professor of neurobiology at Harvard Medical School. Potter suggests via his findings that all Alzheimer's is due to an extra copy of chromosome 21. This explains the early onset of the disease in those with Down Syndrome. In the general population, some cells undergo improper segregation and thus a small percentage of cells have three copies of the chromosome. The presence of these trisomy cells, would therefore cause the disease later than if all the cells of the body had the trisomy (13).

Because those with Down Syndrome already are afflicted with mental retardation, there has not been as much concern over this growing problem. Some, although seemingly indifferent to the problem, believe that, because the inflicted are already impaired, it is not a major concern. When society takes the attitude of such comedians as Bill Maher of ABC, and equates the mentally retarded with "dumb" animals, respect for human life becomes downgraded. Does a human's value come only from the ability of his or her brain to function correctly or should value be placed on all human life simply by virtue of one's belong to the species? How does one argue that it is more acceptable to help one group of people over another, both of whom suffer from the same disease, just because their brains have functioned at different levels? How do we know that the level of understanding in these individuals has not changed, but rather their ability to make us aware of that understanding has? What if the physiology of their brains allows for understanding, but not responding? What do our judgments then become formulated on? Based on the findings it seems apparent that the brain determines the behavior of the body. However, I can not help but hope that there is something innate within all of us that make us more than just behavioral depictions of the models of our brains.

References

1)Introduction to Mental Retardation, Site for National Organization of and for People with Mental Retardation and Related Deveopmental Diabilities and Their Families

2)Education Position Statement, Site for National Organization of and for People with Mental Retardation and Related Deveopmental Diabilities and Their Families

3) Task-Related Social Behavior in Children with Down Syndrome, Site for American Association on Mental Retardation

4)Emotion Recognition by Children With Down Syndrome, Site for American Association on Mental Retardation

5)Mental Retardation and Developmental Disabilities Branch (MRDD), Site for National Institute of Child Heath and Human Development

6)Questions, About Down Syndrome, by Dr. Ira Lott, University of California , Good Site for Alzheimer’s questions

7) Alzheimer's disease, Good Online Encyclopedia

8)New Research Into Down Syndrome Homepage, The link between Alzheimers disease and Down Syndrome, Risk of Down Syndome with Increasing Maternal and Paternal Age, Good Detailed Site

9)Alzheimer's Disease and People with Mental Retardation, Good Detailed Site

10)Developmental Disabilities and Alzheimer's Disease, Good Detailed Site by The Arc

11)Epidemiology of Alzheimer Disease in Mental Retardation, Periodicals Index

12)Fact Sheet: Alzheimer's Disease, Family Caregiver Alliance

13)Harvard Researchers Link Alzheimer's to Problem With Chromosome Segregation Presenilin Proteins are Found in Cell Structures Involved in Mitosis, Recent Press Release

Comments made prior to 2007

I am an educated person and know a great deal about special needs children and adults but I recently have had to learn a great deal about SUNDOWNERS SYNDROME AND ALZHEIMERS DISEASE.

I have been looking for some help and support over my issue.

I am the guardian of a 65 year old uncle who is mentally challenged. He has always functioned at the IQ leve of 57 and adaptive behavior of a pre teen to teenage boy, with high domestic skills.

Over the last seven years I noticed a change in his abilities and care needs.

The GP Doc and I suspected old age symptoms for a while. We did all the MRI EEG etc and no problems. THe last year or so he has failed more. His IZ two years ago dropped to 37. We know that mentally impaired persons abilities deminish at an earlier age and quicker. What I need help with is the dementia part. Maybe I already know the answer but just searching for the what ifs of it.

Do you know where to find other help for patient with SD or ALZ and are also mentally impaired. The doc says dementia for sure. I wander how quickly his dementia can change. I need to make other living arrangement for better care. If anyone out there knows someone in the same type situation, please email me ... Annie, 4 November 2006