Genetic diseases tpe final - 2016

Julia CHAPELAINLou-Ann DESAUNAY Classe de 1ère S2Kim HELLIN

RAPPORT DE TPESUR LES MALADIES

GÉNÉTIQUES

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Contents

Introduction & Generality about genetic

I- Inside the nucleus1. Replication2. Transcription and epigenetic3. Splicing

II- Inside the cytoplasm1. Translation2. Mutations without consequences3. Proteins’ role

III- External actions1. Conditionnal expression2. Environment and lifestyle3. Therapy

Rapport de TPE – Julia Chapelain / Lou-Ann Desaunay / Kim Hellin - Année 2015 – 2016 2

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Conclusion

Rapport de TPE – Julia Chapelain / Lou-Ann Desaunay / Kim Hellin - Année 2015 – 2016

INTRODUCTION&

GENERALITY ABOUT 3

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IntroductionGenetic is a very vast and very complex field. Thanks to the

new technologies and the researches of very important people in the past centuries, scientists discover new things and new questions arise. Those last years, researches have progressed a lot and very fast thanks to the technology. Now, a lot of new things have been discovered, for instance there is the replication of the DNA, the synthesis of a protein or themystery of the epigenetic. All cell of our body are in constant activity, in this way human beings develop themselves in a perfect harmony. However, nothing is perfect and during the unremitting activity of our cell, it is possible that some mistakes happen and generate what we call: genetic diseases. Nevertheless, it exists systems that fix these errors or some ways to avoid their expression. So, a question appears : In what ways the expression of a genetic disease could be avoided even though there is a mutation within genetic program ?

Generality about genetic Humans beings are built from billions and billions of cells.

These cells are constituted of a nucleus, the cytoplasm itself is made up of a many small organisms for instance there are the mitochondria or the vacuole, and the plasma membrane. The genetic information is located inside the nucleus and chromosomes are the genetic information’s shelves. Chromosomes are long threads of DNA, they are always present inside the nucleus, either they are visible either they are invisible. Human beings are made of 23 pairs of chromosome and when they are visible, they are known as « double », they have two chromatids, in other words two arms combined by one centromere. We are able to classify them, in a descending order of size, it is called a karyotype. Among the 46 chromosomes, they are two sexual chromosomes called X and Y, XX define a female and XY a male. DNA is made up of a two complementary strand rolled-up as a double helix; it is a succession of nucleotide. Apiece nucleotide is built of phosphate, deoxyribose


INTRODUCTION&

GENERALITY ABOUT

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and base : A for adenine, T for thymine, C for cytosine and G for guanine. These are complementary base-pairing. A genetic information correspond to an unique location on a chromosome for precise character, defined as a gene, some of them can have different versions : alleles. For instance, there is the eyes colour.


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INSIDE THE NUCLEUS

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1. ReplicationGenes are tiny parts of the DNA, which code for proteins but

also have the genetic information for any living-being. But from DNA to proteins or from a stem cell to two identical daughter cells there are a few mechanisms that we must talk about because they can, without a doubt, avoid a serious genetic disorder. Before talking about those mechanism we ought to talk about the replication which is, has we can probably say, responsible of life if we forget the details. The replication is the system which enables the DNA to duplicate so the other mechanism can make the division of the stem cell in two perfectly identical daughter cells to form a living-being. Here we will mostly talk about human-beings. On the diagram, the DNA is opened thanks to an enzyme called the DNA polymerase. When the DNA molecule is opened, free nucleotides will form a new strand, the non-template strand. The free nucleotides will match the previous one (A-T / T-A / C-G / G-C). The result of the replication is, as we know, two identical DNA molecules.

Previously we talked about how we could avoid a genetic disorder when there is a genetic modification, also called a mutation in the DNA, so now we are going to show the different mechanisms inside the replication that repair the mutations. Even though some mutations can be repaired, not all of them can be. In fact, if the mutations are too important and damage too much the DNA, the replication can be stopped leading to more mutations and sometimes the death of the human-being touched by those alterations.

The first mechanism that we have is the “recombinational repair”, which is a mechanism happening during the replication that fixes the DNA damages. This repair system happens probably more often than we think. In fact, when your skin is too much exposed to the Ultraviolet, called UV, our DNA undergoes some mutations causing thymine dimers. Those dimers can be very dangerous because they change our DNA and can cause disorders and cancers. When the thymine dimers are in our DNA, the replication is blocked and our body has to find a way to fix it. The “recombinational repair”


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can begin to do its work. The first thing we have to know is that it can only work if one of the two strands of the parental DNA is not damaged. When the DNA polymerase has avoided the dimers, there is a gap on the new strand because the DNA polymerase was not able to match the new nucleotides with the dimers. In that case, a matching part on the healthy strand is used to fill the gap in question leaving a new gap on the parental strand but it will be filled again by the polymerase.

The second mechanism happening during the replication is the “error-prone repair”. This mechanism happens when there are mutations in the DNA just as the “recombinational repair” system but instead of using a part of the healthy parental strand, the gap we saw previously is filled with a new DNA that has being synthetized. As the DNA has been synthetized with a damaged DNA, this system fails most of the time and causes some mutations even more serious.

Sometimes, those mechanisms to repair the damaged DNA do not work. For example, the xerodermapigmentosum is a genetic disorder that affects the repair system. When a person who suffers from this disorder is too much exposed to the UV, the thymine dimers appearing in the DNA cannot be repaired. The reason to this issue is a mutation on the gene that produces the enzyme XPf that has to repair the dimers in the DNA and this mutation make the enzyme XPf non-functional leading to more mutations, skin cancer and death of this individual.

2. Transcription and epigeneticThe pre-mRNA is synthesized during the transcription.

This process happens during the interphase. On only one of the two DNA strand and according to a reading direction. Moreover, only genes are transcribed, that’s why if there is a modification on a noncoding part of the DNA there won’t be any consequences during the protein synthesis. However, Scientists don’t know if there could have other consequences. They haven’t paid attention to those parts for a long time that’s why they called it “the junk DNA”.


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First, RNA polymerase breaks the hydrogen liaisons to open the DNA molecule. Then this enzyme sets free nucleotides by complementarity on the transcribed DNA strand. Several pre-mRNA are transcribed at the same time, thanks to this, there is a lot of proteins which are made faster.

However, some mutations on the DNA may not have any consequences. Actually, if a methyl group (CH3) place themselves on a gene it won’t express because the RNA-polymerase couldn’t reach the DNA molecule. The pre-mRNA couldn’t be transcribed. This mechanism is named epigenetic. Genes on which the methyl group are situated are determined by the environment, but that doesn’t alter DNA sequence. However those marks can stay on the DNA even if the signal which had initiated it, isn’t present anymore. Moreover epigenetic has a role in the cell specialization, it show to the cell which gene has to be turned on. The epigenetic is retained during the cell division. However during the gamete manufacture epigenetic is suppressed to permit the embryo’s development, but the epigenetic is hereditary. That means some gene still have epigenetic. Actually, scientists disagree on that point.

This heredity was proved by a study about starvation in Holland in the winter of 1944-1945. Actually, the study says than grandchildren of people who knew starvation are most likely to have diabetes whereas they have never known that. Women who were pregnant during this winter have had children smaller than usual and it is not surprising. But these children’s babies didn’t weigh a lot either. So the starvation’s consequences would affect women’s grandchildren who had known it. Moreover, a study showed that there were a great number of obese people in this population whereas neither their nutrition, neither their way of living can explain it. However, epigenetic anomalies can contribute to develop diseases. As for instance if a methyl group is on a tumor suppressive gene which couldn’t express and couldn’t avoid a tumor.


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3. L’épissageL’épissage correspond à la maturation de l’ARN, c’est-à-dire

que l’ARN prémessager va donner lieu, suite à plusieurs processus à des ARN messagers. Il existe deux épissages différents : l’épissage constitutif et l’épissage alternatif, cependant pour plus de la moitié des gènes humains, ils se superposent. Le premier épissage a pour but de supprimer les introns, soit les parties non-codantes du gène transcrit. Quant au second, il élimine certains exons et conserve les autres, soit les parties codantes, afin de former un ARN messager mature et apte à être traduit. De ce fait, à partir d’un seul ARN prémessager, on peut obtenir plusieurs ARN messager qui coderont donc chacun pour une protéine. Le génome humain est composé d’environ 25 000 gènes, or on estime le nombre ARN messager aux alentours de 100 000, l’épissage permettrait donc en moyenne de donner lieu à partir d’un ARN prémessager à quatre ARN messagers. Ces nombreuses protéines issues à l’origine de la transcription d’un seul gène sont nommées isoformes protéiques.

L’épissage se fait à l’aide de séquences d’ARN présentes dans l’ARN prémessager. Les premières séquences agissent en cis, soit de l’intérieur de l’ARN prémessager, tandis que les autres agissent en trans, donc de l’extérieur. Les séquences cis ont une influence à distance sur l’épissage, elles se situent entre les introns et les exons. Il faut savoir qu’un intron commence toujours par une guanine et un uracile et termine de même toujours par une adénine et une guanine, ils sont ainsi facilement repérables. Grâce à plusieurs complexes, qui vont d’abord identifier l’intron, puis le replier avant de l’éliminer, l’épissage constitutif va pouvoir avoir lieu, une fois supprimé, l’intron est nommé intron excisé. Pour ce qui est de l’épissage alternatif, les processus sont semblables, mais bien plus complexes. Cependant, au lieu de replier uniquement l’intron, les agents responsables de l’épissage vont replier un exon entouré de deux introns, puis les éliminer. En fonction des différentes sortes de cellules, les exons qui s’expriment ne sont pas les mêmes, ce phénomène s’appelle la différenciation.


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Certaines mutations silencieuses, qui n’ont aucun effet sur la synthèse protéique, car le codon code toujours pour le même acide aminé malgré son changement, peuvent cependant avoir un effet sur les épissages. Quelles soient dans les introns ou les exons, cela peut modifier les informations dans les séquences cis et modifier ainsi l’épissage. Les ARN messagers ne sont plus les mêmes et les nouveaux isoformes pourraient voir leur fonction changer par rapport à l’original. Plusieurs maladies découlent de ces mutations dites silencieuses, comme la maladie d’Alzheimer où la protéine tau, deviennent anormales suite à l’insertion de l’exon 10. Ces protéines s’accumulent alors dans le cytoplasme des cellules des neurones et en perturbent le fonctionnement.

L’épissage est un système très complexe qui se déroule après la transcription. Grâce à l’épissage constitutif, qui élimine les introns, et l’épissage alternatif, qui élimine également certains exons, on peut obtenir un grand nombre de protéines dites isoformes, à partir d’un seul ARN prémessager. Toutefois les mutations silencieuses peuvent avoir ici des conséquences sur l’épissage et donner lieu à des maladies génétiques.

After its maturation, the mRNA associates with some proteins to create a ribonucleic complex which is named hnRNP or heterogeneous nuclear ribonucleoprotein. This facility enables the mRNA’s migration by the nuclear pore to the ribosomes.


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INSIDE THE CYTOPLASM

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1. TranslationThe translation is a mechanism that occurs in the cytosol,

which is a part of the cytoplasm. In fact, it follows the migration where the mRNA goes from the nucleus to the cytoplasm. The principal role of the translation is to create proteins. To get this result there are different stages that have to happen in order. The first stage out of three is the initiation. When the mRNA is in the cytosol, the small subunit ribosome will get attached to the mRNA from the beginning of it, to start the translation initiation. As the small subunit ribosome gets to the initiation site, the tRNA comes to match the first codon with an anti-codon. The tRNA is a molecule containing an anti-codon that matches to the mRNA’s codons and it also has an amino acid. Most of the time, the first codon is an AUG it means that the anti-codon is UAC and the amino acid is methionine (met). As the first tRNA has matched the first codon, the large subunit ribosome comes over it to create the to different part of the ribosome, the peptidyl (P) site and the aminoacile (A) site. The initiation is now finished and the second stage can begin.

The second and most important stage is the elongation, where the ribosome moves codon per codon, to translate the mRNA into a protein. When the ribosome moves to the next codon, a new tRNA enters the ribosome at the A site to binds with the mRNA codon then moves to the P site and leave the ribosome. Before it completely leaves it, the tRNA’s amino acid is transferred back to the A site to give it to the new entering tRNA to form a polypeptide. This mechanism continues until the next stage, the termination.

The termination is the last stage of the translation. When the ribosome has moved along the mRNA and gets to the end, the last codon will immediately stop the translation. The reason is that the last codon is a “stop-codon” and no tRNA exists to translate it. So when the “stop codon” is detected, a release factor will enter the ribosome and stop all the actions. The translation is finished and the


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ribosome lets the polypeptide go. The polypeptide will form a protein by itself or thanks to other polypeptides.

Sometimes, the translation is not made correctly because of mutations derived from other mechanism such as the transcription, the replication of the DNA previously, or the replication when the individual was still an egg cell. The result of a non-correct translation can be the synthesis of the wrong protein, of a non-working protein or the translation can be blocked and the protein will not be created. Fortunately, there is a chance that the mutation(s) are silent and without consequences.

2. Les mutations sans conséquencesUne mutation est une modification de la séquence de

nucléotides, elle peut avoir lieu de façon spontanée au cours de l’interphase, lors de la réplication de l’ADN, mais aussi lors de la transcription. Cependant, certaines erreurs échappent aux systèmes de réparation et se transmettent à toutes les cellules issues des divisions cellulaires. Les modifications peuvent aboutir à de graves conséquences comme entrainer la mort de la cellule ou modifier le fonctionnement de celle-ci, mais d’autres demeurent sans conséquences.

On distingue parmi les mutations sans conséquences, les mutations silencieuses. Ces dernières n’ont pas d’impact sur la synthèse protéique puisque le code génétique est redondant, c’est-à-dire qu’un même acide aminé peut être synthétisé à partir de différentes combinaisons d’acides aminés, soit les codons. Par exemple, la leucine est synthétisée à partir des six codons suivants : TTA, TTG, CTT, CTC, CTA et CTG. Les deux sortes de modifications pouvant être silencieuses sont les mutations par substitution et les mutations par inversion. La première correspond à l’échange d’un nucléotide par un autre et la seconde est, comme son nom l’indique, l’inversion de deux nucléotides placés côte à côte. Effectivement, si l’échange d’un nucléotide donne un codon codant pour le même acide aminé, cela n’aura pas d’impact. Si la séquence d’ARN est CTT,


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qui code pour une leucine et que sur la séquence mutée, le dernier T est un A, cela donnera CTA qui code également pour une leucine. De même pour l’inversion, si la séquence D’ARN est CTTA, les trois derniers nucléotides codant pour une leucine, et qu’il y a une inversion entre le C et le T, le codon sera désormais CTA, qui code aussi pour une leucine.

Elle sera aussi sans conséquence si elle touche un gène qui ne sera pas traduit dans la cellule où elle se trouve ou si la mutation touche un gène dont l’allèle est récessif, donc qui ne sera pas celui qui s’exprime, comme la mucoviscidose où il faut être homozygote pour être atteint de la maladie.

De plus, lorsqu’une mutation induit le changement d’un acide aminé, dans certain cas, si le nouvel acide aminé a les mêmes propriétés que l’ancien ou en fonction de sa place dans la chaine, cela peut ne pas avoir d’effet. Par exemple, pour le cas de la drépanocytose, maladie génétique qui est du à l’échange d’un acide aminé hydrophile par un hydrophobe situé à l’extérieur de la chaine bêta, cela provoque un changement de la forme des globules rouges. Si l’erreur avait donné lieu à un autre acide aminé hydrophile ou s’il était situé à l’intérieur de la chaine, cela n’aurait pas eu d’impact sur la forme des globules rouges.

Les mutations sont des phénomènes rares qui se produisent lors du cycle cellulaire, bien qu’il existe plusieurs systèmes de réparation de l’ADN efficaces, quelques erreurs perdurent. Cependant, toutes n’ont pas de conséquences sur la cellule. En effet, dans certains cas, comme par exemple si la mutation ne touche pas un gène ou bien si la mutation est dite silencieuse.


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3. Proteins’ roleProteins are very varied and have an important role in our

organism. As actine which take part in the muscular contraction, it is a functional movement.

But this one has also other functions. Indeed, it has a structural role, the actine protein is present in the cytoskeleton, a fibrous layout which is in every cells. This structure serves to bring a minimal stiffness to cells. Actine serves to generate internals movements. As, for instance the chromosome displacement during the cellular division.

However there are others proteins like DNA polymerase which has an enzymatic function, as antibody which has a defensive role, or the insulin that has a hormonal function.

When a protein is mutated, there can be serious consequences even if only one amino acid is different from the original protein. Take the case of phenylketonuria (PH), this disease appears because of a mutation in the gene PAH coding for the phenylalanine hydroxylase protein. Because of this disease, the transformation of the indispensable amino acid phenylalanine present in the food into tyrosine, a non-essential amino acid cannot happen. That’s why there is a surplus of phenylalanine in the blood which can involve a lot of consequences. As, for instance the irreversible and progressive neuron deterioration which can lead to intellectual deficiency and behavioral disorder. But this surplus involves growth lateness, spasm, eczema or vomiting. Moreover, the tyrosine lake leads to pale hair and skin. Fortunately, those symptoms can be avoid or reduce. If the disease is detect enough early. Well, in France all the people who are sick are known thanks to the phenylalanine concentration test which is carried out on infants at their third day. So a diet poor in phenylalanine is put in place for sick people.

The phenotype is all the characteristics that are observables on a person. We can observe it at different


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scales. They are: the organism level, it is the macroscopic phenotype, the cell level that explain what happened in the cell and the molecule level, it is in the protein.


EXTERNAL ACTIONS

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1. Expression conditionnelleCertaines maladies n’apparaissent que dans des conditions

précises comme l’élévation de la température ou le niveau d’hydratation.

C’est le cas par exemple de la drépanocytose, les effets ne se produisent que dans un milieu faible en dioxygène. Cette maladie est due à une mutation du gène codant pour la chaine d’acide aminé bêta de l’hémoglobine sur le chromosome 11. La mutation intervient sur le 17ème nucléotide du gène (T devient A) ce qui influence le sixième codon et donc le sixième acide aminé. L’acide aminé original était un acide glutamique mais, il devient alors une valine. Malheureusement, ces deux acides aminés ne se comportent pas de la même façon. Effectivement, le nouvel acide aminé, contrairement à l’ancien est hydrophobe.

Lorsqu’une personne fait du sport, plus de dioxygène circule dans le sang mais après que le sang soit passé dans les muscles, la concentration en dioxygène est moins importante que lorsque l’organisme est au repos. L’acide aminée valine qui est à l’extérieur de la chaine forme alors une liaison hydrophobe avec la phénylalanine en position 85 et la leucine en position 88. . Il se crée une chaine de bêta-globine morbide qui se colle à la paroi du globule rouge désoxygéné. Le globule rouge prend alors la forme d’une faucille. Cette forme réduit leur souplesse, c’est pourquoi lorsqu’ils doivent passer dans des petits capillaires, ils se cassent. A cause de ce phénomène, il n’y a pas un grand nombre de globules rouges dans le sang des drépanocytaires, et les hématies qui restent transportent moins de dioxygène que la normale. De plus, lors de l’hémolyse des globules rouges l’hémoglobine est relâchée dans le sang ce qui détruit le monoxyde d’azote. Une molécule permettant la dilatation des vaisseaux et donc un bon flux sanguin. La destruction des hématies relâche aussi de l’hème, une substance nocive pour l’endothélium des vaisseaux sanguins. L’anémie, un manque de globules rouges est l’un des premiers symptômes. Elle peut se traduire par une pâleur et de la fatigue. Cependant elle peut


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être aggravée si la rate s’épuise dans la destruction de globules rouges ou si, dans les cas les plus extrêmes, la production des globules rouges s’arrête. Il y a aussi de fortes douleurs au niveau des articulations et des os dû à l’obstruction des vaisseaux sanguins. Chez les bébés et les nourrissons, il peut y avoir des gonflements douloureux des pieds et des mains. Il y a des risques d’AVC plus élevés durant ces crises. Elles peuvent aussi affecter les poumons compromettant ainsi l’oxygénation de tout l’organisme. Les risques d’infections sont plus présent et au fil des années, il peut y avoir des complications sur quasiment toutes les organes, cette maladie peut aussi engendrer un retard de croissance. Pour traiter cette maladie, il faut tout d’abord prévenir les infections en administrant plus d’antibiotiques et de vaccins. Il faut aussi mettre en place un régime et une bonne hydratation afin d’éviter les crises douloureuses. Lors d’anémie, on peut faire des transfusions sanguines, et dans les cas les plus graves de drépanocytaires, on peut aussi faire des greffes de moelle osseuse, mais seulement s’il y a des donneurs compatibles. De plus, lors des crises vaso-occlusives, les antalgiques et dans les cas les plus extrêmes, de la morphine peuvent soulager les malades. Cependant, des chercheurs sont en train d’élaborer des traitements géniques afin de greffer des gènes sains dans les cellules souches des drépanocytaires.

2. Environment and lifestyleThe environment or the lifestyle can affect some genetic

diseases, these diseases are known as “multifunctional”. They are for the most part polygenic, in other words several gene are concerned. The environment is defined by what we can’t act on, that is pollution or else climate amongst others. As for lifestyle, it is quite the reverse, on what we can act, as nutrition or practice of sport. Consequently it is possible to reduce the chances to be suffering to this kind of disease or, when someone suffers from a genetic disorder, it can restrict its expression.


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Phenylketonuria (PKU) is a rare genetic disease of metabolism; people affected by this disorder have an abnormal accumulation of an amino acid, the phenylalanine. The excess of this amino acid, present in foodstuffs especially in proteins, cause a progressive and irreversible destruction of neurons, which leads to a serious mental retardation. It is foreseeable to prevent the symptoms of phenylketonuria if during the childhood; a very strict diet is set up. In that case, the symptoms of this disease won’t appear, but following accurate amount and forbidden food like meat, fish or cereal is compulsory in order to keep the rate of phenylalanine in conformity. Following this strict diet after a screening can also regulates the rate of phenylalanine and in this way, symptoms can be less important.

In this way, it is possible to avoid the symptoms of some genetic diseases or at least reduce the seriousness of these symptoms. As far as multifunctional diseases, people can have genetic predispositions but in the same way as phenylketonuria or other genetic disorders, a specific lifestyle or another environment can prevent the symptoms to happen. For example there is the Alzheimer’s disease, however scientists are caring out extensive research to discover the kind of lifestyle that influences it.

3. TherapyThe last way to avoid and cure a genetic disorder is of course

the therapy. Today, therapy becomes very important in the medical world because, thanks to the medical progress, we have discovered new ways to treat disorders formerly incurable. We call this experimental therapy, the gene therapy because the genetic disorder is treated with genes only. This therapy has been used for a long time, in fact in 1989, there was the first successful DNA transfer in the human body and year later it was used by another scientist for a therapeutic use. At the moment we can count three different approaches to use this therapy still experimental.


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The first way is to deactivate the mutated gene. It’s called the gene silencing and it’s not an easy approach. This therapy is used to fix genes in the human DNA when there is a mutation. To avoid the serious consequences produced by a mutation, this gene silencing’s goal is to prevent the transcription thanks to a “triple-helix-forming oligonucleotide “. We know that the DNA molecule is a double helix but when a gene is mutated, we use an oligonucleotide, which is a short DNA molecule, to form a triple-helix and then block the transcription of the mutated gene. The second way is similar as the first one because it is also a gene silencing therapy. Contrary to the first way to deactivate the mutated gene, a new DNA strand is not added, it’s a ribozyme, which is an RNA molecule, and also an enzyme presents in the ribosome during the translation. This time, the translation will be prevented. After the transcription, the mutated strand has become a mutated mRNA but the ribozyme has specific role : it will get attached to the mutated mRNA and will destroy it. Since there is no more mRNA, the translation cannot happen. Moreover there is no more mutation. The last approach is to modify the individual’s immune cells to give them another role, which is, according to theNational Center for Research Resources: “(that) When returned to the patient, these modified cells will find and destroy any cells that carry the antigen.” Today the gene therapy is getting more popular and successes are frequent especially for blood disorders, hereditary diseases, hemophilia ect… Maybe someday, it will even be possible to heal any genetic disorders

ConclusionBy way of conclusion, the genetic disease’s expression can be

avoided thanks to a lot of mechanisms in the cell or in the organism level. In the nucleus, repairs systems prevent mutations, while epigenetic and splicing may avoid them to express. Likewise, in the cytoplasm, the genetic code’s repetition can avoid a change of


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amino acid. Moreover, the same behavior between two amino acids can reduce the consequences. And a healthy way of living, a good environment and sometimes a therapy can reduce or stop the disease’s expression.

En ouverture nous allons parler d’un moyen, encore en train de se développer, permettant d’éviter que les maladies génétiques graves, rares et héréditaires ne touchent un foetus lors de son développement dans l’utérus de la mère. En effet, d’après le TIME de janvier 2003, des scientifiques américains ont mis au point une techniquepour retirer le noyau de la cellule œuf de l'utérus puis l'introduire dans une autre cellule œuf humain en prenant soin de ne pas laisser l’ADN mitochondrial, car c’est cet ADN qui provoque les maladies du même nom/mitochondriale… D’après des études, nous pouvons compter qu’un enfant sur 10,000 est atteint de ce genre de maladie, qui se trouve incurable et peut engendrer des maladies neurologiques, des malformations et bien d’autres maladies. Cette nouvelle technique et une avancée primordiale pour le monde de la recherche mais également le monde de la médecine.


Science

Genetic diseases tpe final - 2016