Genetic diseases tpe final - 2016

Julia CHAPELAIN
Lou-Ann DESAUNAY Classe de 1ère S2
Kim HELLIN
RAPPORT DE TPE
SUR LES MALADIES
GÉNÉTIQUES

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Rapport de TPE – Julia Chapelain / Lou-Ann Desaunay / Kim Hellin - Année 2015 – 2016
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Contents
Introduction & Generality about genetic
I- Inside the nucleus
1. Replication
2. Transcription and epigenetic
3. Splicing
II- Inside the cytoplasm
1. Translation
2. Mutations without consequences
3. Proteins’ role
III- External actions
1. Conditionnal expression
2. Environment and lifestyle
3. Therapy
Conclusion

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INTRODUCTION
&
GENERALITY ABOUT
GENETIC

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Introduction
Genetic 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 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. Replication
Genes 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 insidethe 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” 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

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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. Thereason 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 epigenetic
The 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”.
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

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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.

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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.
3. L’épissage
L’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 mêmetoujours 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. Translation
The 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 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

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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 conséquences
Une mutation est une modification de la séquence de nucléotides, elle peut
avoir lieu de façon spontanée au cours del’interphase,lors dela 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, 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 uneleucine, et qu’il y a une inversion entre leC 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.

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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 netouche pas
un gène ou bien si la mutation est dite silencieuse.

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3. Proteins’ role
Proteins 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 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.

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EXTERNAL
ACTIONS

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1. Expression conditionnelle
Certaines 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 del’hémoglobine sur le chromosome11.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 quelorsque l’organisme est au repos.L’acide aminéevalinequi 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
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

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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’élabor er
des traitements géniques afin de greffer des gènes sains dans les cellules souches
des drépanocytaires.
2. Environment and lifestyle
The 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.
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.

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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. Therapy
The 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.
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

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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
Conclusion
By 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 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
netouchent 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.

Genetic diseases tpe final - 2016

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