Hoi, Misschien een stomme vraag, maar waarom heeft een individu met een trisomie (maakt niet uit welke, maar 21 is het bekendste) een afwijking. De drie aanwezige chromosomen 21 zijn zelf toch gezond? Komt dit door een overexpressie van eiwitten(en waarom is dat dan) of wat anders? Mij leek het namelijk dat het niet uitmaakt welk chromosoom er wordt afgelezen en het dus niet uitmaakt of je er nou 3 of 2 hebt, maar dit is dus niet de praktijk.
Alvast bedankt,
Gr Jan
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Waarom afwijking bij trisomie
Moderator: ArcherBarry
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- Berichten: 6.058
Re: Waarom afwijking bij trisomie
The chromosomes are holders of the genes, those bits of DNA that direct the production of a wide array of materials the body needs. This direction by the gene is called the gene's "expression." In trisomy 21, the presence of an extra set of genes leads to overexpression of the involved genes, leading to increased production of certain products. For most genes, their overexpression has little effect due to the body's regulating mechanisms of genes and their products. But the genes that cause Down syndrome appear to be exceptions.
Which genes are involved? That's been the question researchers have asked ever since the third 21st chromosome was found. From years of research, one popular theory stated that only a small portion of the 21st chromosome actually needed to be triplicated to get the effects seen in Down syndrome; this was called the Down Syndrome Critical Region. However, this region is not one small isolated spot, but most likely several areas that are not necessarily side by side. The 21st chromosome may actually hold 200 to 250 genes (being the smallest chromosome in the body in terms of total number of genes); but it's estimated that only a small percentage of those may eventually be involved in producing the features of Down syndrome. Right now, the question of which genes do what is highly speculative. However, there are some suspects.
Genes that may have input into Down syndrome include:
* Superoxide Dismutase (SOD1)-- overexpression may cause premature aging and decreased function of the immune system; its role in Senile Dementia of the Alzheimer's type or decreased cognition is still speculative
* COL6A1 -- overexpression may be the cause of heart defects
* ETS2 -- overexpression may be the cause of skeletal abnormalities
* CAF1A -- overexpression may be detrimental to DNA synthesis
* Cystathione Beta Synthase (CBS) -- overexpression may disrupt metabolism and DNA repair
* DYRK -- overexpression may be the cause of mental retardation
* CRYA1 -- overexpression may be the cause of cataracts
* GART -- overexpression may disrupt DNA synthesis and repair
* IFNAR -- the gene for expression of Interferon, overexpression may interfere with the immune system as well as other organ systems
Other genes that are also suspects include APP, GLUR5, S100B, TAM, PFKL, and a few others. Again, it is important to note that no gene has yet been fully linked to any feature associated with Down syndrome.
One of the more notable aspects of Down syndrome is the wide variety of features and characteristics of people with trisomy 21: There is a wide range of mental retardation and developmental delay noted among children with Down syndrome. Some babies are born with heart defects and others aren't. Some children have associated illnesses such as epilepsy, hypothyroidism or celiac disease, and others don't. The first possible reason is the difference in the genes that are triplicated. As I mentioned above, genes can come in different alternate forms, called "alleles." The effect of overexpression of genes may depend on which allele is present in the person with trisomy 21. The second reason that might be involved is called "penetrance." If one allele causes a condition to be present in some people but not others, that is called "variable penetrance," and that appears to be what happens with trisomy 21: the alleles don't do the same thing to every person who has it. Both reasons may be why there is such variation in children and adults with Down syndrome.
http://www.ds-health.com/trisomy.htm
Which genes are involved? That's been the question researchers have asked ever since the third 21st chromosome was found. From years of research, one popular theory stated that only a small portion of the 21st chromosome actually needed to be triplicated to get the effects seen in Down syndrome; this was called the Down Syndrome Critical Region. However, this region is not one small isolated spot, but most likely several areas that are not necessarily side by side. The 21st chromosome may actually hold 200 to 250 genes (being the smallest chromosome in the body in terms of total number of genes); but it's estimated that only a small percentage of those may eventually be involved in producing the features of Down syndrome. Right now, the question of which genes do what is highly speculative. However, there are some suspects.
Genes that may have input into Down syndrome include:
* Superoxide Dismutase (SOD1)-- overexpression may cause premature aging and decreased function of the immune system; its role in Senile Dementia of the Alzheimer's type or decreased cognition is still speculative
* COL6A1 -- overexpression may be the cause of heart defects
* ETS2 -- overexpression may be the cause of skeletal abnormalities
* CAF1A -- overexpression may be detrimental to DNA synthesis
* Cystathione Beta Synthase (CBS) -- overexpression may disrupt metabolism and DNA repair
* DYRK -- overexpression may be the cause of mental retardation
* CRYA1 -- overexpression may be the cause of cataracts
* GART -- overexpression may disrupt DNA synthesis and repair
* IFNAR -- the gene for expression of Interferon, overexpression may interfere with the immune system as well as other organ systems
Other genes that are also suspects include APP, GLUR5, S100B, TAM, PFKL, and a few others. Again, it is important to note that no gene has yet been fully linked to any feature associated with Down syndrome.
One of the more notable aspects of Down syndrome is the wide variety of features and characteristics of people with trisomy 21: There is a wide range of mental retardation and developmental delay noted among children with Down syndrome. Some babies are born with heart defects and others aren't. Some children have associated illnesses such as epilepsy, hypothyroidism or celiac disease, and others don't. The first possible reason is the difference in the genes that are triplicated. As I mentioned above, genes can come in different alternate forms, called "alleles." The effect of overexpression of genes may depend on which allele is present in the person with trisomy 21. The second reason that might be involved is called "penetrance." If one allele causes a condition to be present in some people but not others, that is called "variable penetrance," and that appears to be what happens with trisomy 21: the alleles don't do the same thing to every person who has it. Both reasons may be why there is such variation in children and adults with Down syndrome.
http://www.ds-health.com/trisomy.htm
That which can be asserted without evidence can be dismissed without evidence.
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- Berichten: 339
Re: Waarom afwijking bij trisomie
Een toevoeging, wat in bovenstaande niet zo goed tot uiting komt: de meeste trisomieën lijden tot ernstige afwijkingen - zo ernstig dat ze niet levensvatbaar zijn. Trisomie 13/18/21 zijn levensvatbaar. Ook meer kopieën van het X-chromosoom is levensvatbaar (XXY, XXXY), maar dat komt omdat het teveel daar wordt uitgeschakeld (dmv. X-inactivatie). Het fenomeen X-inactivatie is bedoeld om vrouwen te beschermen tegen overactiviteit van genen op het X-chromosoom (c.q. mannen te beschermen tegen een tekort).
Met groet,
Gesp
Met groet,
Gesp
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- Berichten: 829
Re: Waarom afwijking bij trisomie
Bovendien blijkt een mentale handicap juist te wijten te zijn aan een overproductie van eiwitten, wat hoopgevend is, want het is makkelijker om een overproductie te verminderen dan iets wat niet geproduceert wordt toe te voegen
"Als je niet leeft zoals je denkt, zul je snel gaan denken zoals je leeft."
--Vladimir Lenin-- (Владимир Ильич Ульянов)
--Vladimir Lenin-- (Владимир Ильич Ульянов)
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- Berichten: 6.058
Re: Waarom afwijking bij trisomie
Een toevoeging, wat in bovenstaande niet zo goed tot uiting komt: de meeste trisomieën lijden tot ernstige afwijkingen - zo ernstig dat ze niet levensvatbaar zijn. Trisomie 13/18/21 zijn levensvatbaar. Ook meer kopieën van het X-chromosoom is levensvatbaar (XXY, XXXY), maar dat komt omdat het teveel daar wordt uitgeschakeld (dmv. X-inactivatie). Het fenomeen X-inactivatie is bedoeld om vrouwen te beschermen tegen overactiviteit van genen op het X-chromosoom (c.q. mannen te beschermen tegen een tekort).
Ook meer kopieën van het Y-chromosoom is levensvatbaar
That which can be asserted without evidence can be dismissed without evidence.
