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St. Attri Public School

"Genes And Genetic Disorders"

Submitted To: Submitted By:-

Mr. Paramjeet Sonker Bharti Sharma

M.Sc. Biotechnoloy !lass:-#th

$oll %o.&

1



!erti'icate

This is to certify that the project entitled, “Genes And

Genetic Disorders" submitted by "Bharati Sharma" Roll

No. "&"in partial fulfillment of the requirements of for the

award of "(th !lass" at the "St. Attri Public School" is an

authentic work carried out by her under my supervision and

uidance.

To the best of my knowlede, the matter embodied in the

project has not been submitted to any other !chool.

ate#

$r. %aramjeet !onkar

2



Ackno)ledement& wish to e'press my sincere ratitude to people who have

directly or indirectly contributed. (n this report & have been

proportions to be blessed with $r. %aramjeet !onkar as my

mentor. & feel that he was the appropriate choice and & shall

remain oblied to him life lon .& have learnt to be well

manaed, punctual, )ssidicous and at the same time , not to

ive up to ticklish times. & have absolutely no words to

e'press my feelins for this lab.& wish to e'press my sincere

appreciation to $r. %aramjeet !onkar for his valuable

uidance, supervision and understandin throuhout the project work he made this study possible by helpin and

encouraement me in all stae of my project work he made

this story possible by helpin and encouraement me in all

stae of my project work. & wish to e'tent my thanks to for

helpin me in the project. $y special thanks are due to $r.

%aramjeet !onkar

3



*ntroduction

&t is the differences that matter. *ou share about +- of your enes

with your do but it is the remainin doy/ enes 0 those whichmake dos have puppies not babies or kittens 0 that we see as

important. 1ertainly it is the differences between people that interest

us when it comes to health and disease. 2hy do some live a lon and

healthy life, whilst others develop life3threatenin, chronic diseases in

mid3life or indeed are born with a disorder4

) popular response nowadays is to assume most of the difference lies

in our N)/ 0 in the 5.6- that we don/t have in common with

everyone else. This is understandable iven the e'citementsurroundin the 7uman 8enome %roject and the ubiquitous use of the

N) double heli' icon in all thins biomedical. 9ut N) alone is not

destiny.

7uman development from conception to adulthood is an inseparable

partnership,

moulded within our cells, of Nature :the N) we inherit; and Nurture

:the prevailin nutritional, social and physical environment;. (ur

N) specifies the structure of proteins 0 the primary chemical

buildin blocks of life 0 but it is the cell/s circumstances that

ultimately determine when, where and how much of these proteins are

produced. The response may be a transient adjustment, but sometimes

our cells chane for life, makin different orans as the embryo

develops or when a child/s life trajectory adjusts to the world in which

the child finds itself.

The study of these endurin chanes, where life meets the enome, is

epienetic.

<pienetic discoveries will impact upon our understandin of child

development, mentalhealth, and how public health and well3bein can

be maintained in a chanin world.

8enetics and epienetic o hand3in3hand, so this introductory booklet

covers both. $uch of human enetic variation is a consequence,

throuh natural selection, of life challenin encounters durin our

evolutionary history. $uch can be learned when this evolved system

fails to cope and manifests as disease.

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+hat Are Genes,

) ene is the basic physical and functional unit of heredity. 8enes,which are made up of N), act as instructions to make molecules

called proteins. &n humans, enes vary in si=e from a few hundred

N) bases to more than > million bases. The 7uman 8enome %roject

has estimated that humans have between >5,555 and >,555 enes.

<very person has two copies of each ene, one inherited from each

parent. $ost enes are the same in all people, but a small number of

enes :less than 6 percent of the total; are slihtly different between people. )lleles are forms of the same ene with small differences in

their sequence of N) bases. These small differences contribute to

each person/s unique physical features.

5



D%A

N) contains four chemicals :adenine, thymine, cytosine, and

uanine ? called ), T, 1, and 8 for short; that are strun in patterns

on e'tremely thin, coiled strands in the cell. 7ow thin4 1ells are tiny

? invisible to the naked eye ? and each cell in your body contains

about @ feet of N) thread, for a total of about A billion miles of

N) inside youB

!o where do enes come in4 8enes are made of N), and different

patterns of ), T, 8, and 1 code for the instructions for makin thins

your body needs to function :like the en=ymes to diest food or the

piment that ives your eyes their color;. )s your cells duplicate, they pass this enetic information to the new cells.

N) is wrapped toether to form structures called chromosomes.

$ost cells in the human body have >A pairs of chromosomes, makin

a total of C@. &ndividual sperm and e cells, however, have just >A

unpaired chromosomes. *ou received half of your chromosomes from

your motherDs e and the other half from your fatherDs sperm cell. )

male child receives an E chromosome from his mother and a *chromosome from his fatherF females et an E chromosome from

each parent.

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eredity

7eredity is the passin of enes from one eneration to the ne't. *ou

inherit your parentsD enes. 7eredity helps to make you the person

you are today# short or tall, with black hair or blond, with brown eyes

or blue.

your enes can determine whether youDll be a straiht3) student or a

reat athlete 7eredity plays an important role, but your environment

:includin thins like the foods you eat and the people you interact

with; also influences your abilities and interests.

) person can have chanes :or mutations; in a ene that can causemany issues for them. !ometimes chanes cause little differences, like

hair color. (ther chanes in enes can cause health problems.

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Mutation

$utations in a ene usually end up causin that particular ene copy

to not do its job the way it normally should. !ince we have two copies

of every ene, typically thereDs still a "normal" workin copy of the

ene. &n these cases, usually nothin out of the ordinary happens since

the body can still do the jobs it needs to do. This is an e'ample of an

autosomalrecessie trait.

Researchers have identified more than C,555 diseases that are caused by mutations. 9ut havin a enetic mutation that may cause a disease

or condition doesnDt always mean that a person will actually develop

that disease or condition.

(n averae, people probably carry from to 65 enes with mutations

in each of their cells. %roblems happen when the particular ene is

dominant or when a mutation is present in both copies of a recessive

ene pair. %roblems can also happen when several variant enes

interact with each other ? or with the environment ? to increasesusceptibility to diseases.

Genetic Disease and Disorders

) enetic disorder is a enetic problem caused by one or more

abnormalities in the enes, especially a condition that is present from

birth :conenital;. $ost enetic disorders are quite rare and affect one

person in every several thousands or millions.

8enetic disorders may or may not be heritable, i.e., passed down from

the parentsD enes. &n non3heritable enetic disorders, defects may be

caused by new mutations or chanes to the N). &n such cases, the

defect will only be heritable if it occurs in the erm line. The same

disease, such as some forms of cancer, may be caused by an inherited

enetic condition in some people, by new mutations in other people,

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and mainly by environmental causes in still other people. 2hether,

when and to what e'tent a person with the enetic defect or

abnormality will actually suffer from the disease is almost always

affected by the environmental factors and events in the personDsdevelopment.

Single-gene

) sinle-ene disorder is the result of a sinle mutated ene. (ver

C555 human diseases are caused by sinle3ene defects. !inle3ene

disorders can be passed on to subsequent enerations in several ways.

8enomic imprintin and uniparental disomy, however, may affectinheritance patterns. The divisions between recessive and dominant

types are not "hard and fast", althouh the divisions between

autosomal and E3linked types are :since the latter types are

distinuished purely based on the chromosomal location of the ene;.

Gor e'ample, achondroplasia is typically considered a dominant

disorder, but children with two enes for achondroplasia have a severe

skeletal disorder of which achondroplasics could be viewed as

carriers. !ickle3cell anemia is also considered a recessive condition, but hetero=yous carriers have increased resistance to malaria in early

childhood, which could be described as a related dominant condition.

2hen a couple where one partner or both are sufferers or carriers of a

sinle3ene disorder wish to have a child, they can do so throuh in

vitro fertili=ation, which means they can then have a preimplantation

enetic dianosis to check whether the embryo has the enetic

disorder.

&f a person has a chane in a dominant ene that is associated with a

particular condition, he or she will usually have features of that

condition. )nd, each of the personDs children will have a 6 in > :5-;

chance of inheritin the ene and developin the same features.

iseases and conditions caused by a dominant ene include

achondroplasia :pronounced# ay3kon3druh3%H)*3=huh, a form of

dwarfism;,$arfan !yndrome :a connective tissue disorder;, and

7untinton disease :a deenerative disease of the nervous system;.

9



%eople who have a chane in just one copy of a recessive ene are

called "carriers." They donDt usually have the disease because they

have a normal ene copy of that pair that can do the job. 2hen two

carriers have a child toether, however, the child has a 6 in C :>-;

chance of ettin a ene with a mutation from both parents, which

would result in the child havin the disease. 1ystic Gibrosis :a lun

disease;, !ickle 1ell )nemia:a blood disorder;, and Tay3!achs disease

:which causes nervous system problems; are caused by recessive

mutations from both parents comin toether in a child.

2ith recessive ene mutations on the E chromosome, usually only

uys can develop the disease because they have only one E

chromosome. 8irls have two E chromosomes ? since they have a back3up copy of another E chromosome, they donDt always show

features of E3linked conditions. These include the bleedin disorder

hemophilia:pronounced# hee3muh3G&H3ee3uh; and color blindness.

!ometimes when an e and sperm unite, the new cell ets too many

or too few chromosomes, which can cause issues for the child. Gor

e'ample, most children born with own syndrome have an e'tra

chromosome number >6.

Autosomal recessie

Two copies of the ene must be mutated for a person to be affected by

an autosomal recessive disorder. )n affected person usually has

unaffected parents who each carry a sinle copy of the mutated ene

:and are referred to as carriers;. Two unaffected people who each

carry one copy of the mutated ene have a >- risk with each

prenancy of havin a child affected by the disorder. <'amples of this

type of disorder are )lbinism, $edium3chain acyl31o)

dehydroenase deficiency, cystic fibrosis, sickle3cell disease, Tay3

!achs disease, Niemann3%ick disease, spinal muscular atrophy, and

Roberts syndrome. 1ertain other phenotypes, such as wet versus dry

earwa', are also determined in an autosomal recessive fashion.

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/-linked dominant

E3linked dominant disorders are caused by mutations in enes on the

E chromosome. (nly a few disorders have this inheritance pattern,

with a prime e'ample bein E3linked hypophosphatemic rickets.$ales and females are both affected in these disorders, with males

typically bein more severely affected than females. !ome E3linked

dominant conditions, such as Rett syndrome, incontinentia pimenti

type >, and )icardi syndrome, are usually fatal in males either in

utero or shortly after birth, and are therefore predominantly seen in

females. <'ceptions to this findin are e'tremely rare cases in which

boys with Ilinefelter syndrome :C+,EE*; also inherit an E3linkeddominant condition and e'hibit symptoms more similar to those of a

female in terms of disease severity. The chance of passin on an E3

linked dominant disorder differs between men and women. The sons

of a man with an E3linked dominant disorder will all be unaffected

:since they receive their fatherDs * chromosome;, and his dauhters

will all inherit the condition. ) woman with an E3linked dominant

disorder has a 5- chance of havin an affected fetus with each prenancy, althouh it should be noted that in cases such as

incontinentia pimenti, only female offsprin are enerally viable. &n

addition, althouh these conditions do not alter fertility per se,

individuals with Rett syndrome or )icardi syndrome rarely reproduce.

/-linked recessie

E3linked recessive conditions are also caused by mutations in eneson the E chromosome. $ales are more frequently affected than

females, and the chance of passin on the disorder differs between

men and women. The sons of a man with an E3linked recessive

disorder will not be affected, and his dauhters will carry one copy of

the mutated ene. ) woman who is a carrier of an E3linked recessive

disorder :ER Er ; has a 5- chance of havin sons who are affected

and a 5- chance of havin dauhters who carry one copy of themutated ene and are therefore carriers. E3linked recessive conditions

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include the serious diseases hemophilia ), uchenne muscular

dystrophy, and Hesch3Nyhan syndrome, as well as common and less

serious conditions such as male pattern baldness and red3reen color

blindness. E3linked recessive conditions can sometimes manifest infemales due to skewed E3inactivation or monosomy E :Turner

syndrome;.

0-linked

*3linked disorders, also called holandric disorders, are caused by

mutations on the * chromosome. These conditions display may only

be transmitted from the heteroametic se' :e.. male humans; tooffsprin of the same se'. $ore simply, this means that *3linked

disorders in humans can only be passed from men to their sonsF

females can never be affected because they do not possess *

allosomes.

*3linked disorders are e'ceedinly rare but the most well3known

e'amples typically cause infertility. Reproduction in such conditions

is only possible throuh the circumvention of infertility by medical

intervention.

Mitochondrial

This type of inheritance, also known as maternal inheritance, applies

to enes in mitochondrial N). 9ecause only e cells contribute

mitochondria to the developin embryo, only mothers can pass on

mitochondrial conditions to their children. )n e'ample of this type of

disorder is HeberDs hereditary optic neuropathy.

Some o' the Sinle Gene Disorders are as 'ollo)s

1ystic fibrosis is a enetic disorder that affects the respiratory and

diestive systems.

%eople with cystic fibrosis inherit a defective ene on chromosome +called CFTR :cystic fibrosis transmembrane conductance reulator;.

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The protein produced by this ene normally helps salt :sodium

chloride; move in and out of cells. &f the protein doesnDt work

correctly, that movement is blocked and an abnormally thick sticky

mucus is produced on the outside of the cell. The cells most seriously

affected by this are the lun cells. This mucus clos the airways in the

luns, and increases the risk of infection by bacteria.

The thick mucus also blocks ducts in the pancreas, so diestive

en=ymes canDt et into the intestines. 2ithout these en=ymes, the

intestines cannot properly diest food. %eople who have the disorder

often do not et the nutrition they need to row normally.

Ginally, cystic fibrosis affects the sweat lands. Too much salt is lostthrouh sweat, which can disrupt the delicate balance of minerals in

the body.

Sym1toms And Dianosis

!ymptoms of cystic fibrosis can include couhin or whee=in,

respiratory illnesses :such as pneumonia or bronchitis;, low weiht,

salty3tastin skin, and reasy stools. 9ecause the luns are cloed

and repeatedly infected, lun cells donDt last as lon as they should.

13



Therefore, cystic fibrosis patients who donDt receive treatment have

shortened lifespans.

%eople with cystic fibrosis have between > and times the normal

amount of salt in their sweat. Thus, doctors can use a sweat test to

measure the amount of salt :sodium chloride; in a personDs sweat.

!weat is collected from the personDs arm or le and taken to a

laboratory to be analy=ed.

&n newborns, doctors can measure the amount of a protein called

trypsinoen in the blood. The level of this protein is hiher than

normal in people with cystic fibrosis.

Ginally, enetic tests can identify a faulty 1GTR ene usin a sample

of the patientDs blood.

1ystic 'ibrosis treatement

)lthouh there is no cure for cystic fibrosis, new treatments are

helpin people with the disease live loner than before. $ost

treatments work by clearin mucus from the luns and preventin

lun infections. 1ommon treatments include#

• 1hest physical therapy, in which the patient is repeatedly clapped on the

back to free up mucus in the chest

• &nhaled antibiotics to kill the bacteria that cause lun infections

•

9ronchodilators :also used by people with asthma; that help keep theairways open

• %ancreatic en=yme replacement therapy to allow proper food diestion

8ene therapy :a treatment currently in clinical trials;, in which the

healthy CFTR ene is inserted into the lun cells of a patient to correct

the defective ene

2.Galactosemia

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8alactosemia is a rare disorder that affects the bodyDs ability to break

down a food suar called alactose :found in milk and other dairy

products;.

The body breaks down lactose into alactose and lucose and uses

these suars for enery. $ost people with alactosemia are missin an

en=yme :called 8)HT; that helps further break down alactose.

efects in alactose metabolism cause to'ic chemicals to build up in

cells of the body.

Dianosis And Treatment

efects in alactose metabolism can cause several severe symptoms,

includin kidney failure, an enlared liver, cataracts :cloudin of the

eye lens;, poor rowth, and intellectual disability.

%eople can inherit a milder form of the disorder when a different

ene, also involved in alactose metabolism, is mutated. These

patients often suffer from cataracts, but not the other symptomsassociated with classical alactosemia.

&n most states, babies are tested for alactosemia at birth. Jsin a tiny

blood sample taken from the babyDs heel, the test checks for low levels

of the 8)HT en=yme. This allows for prompt treatment, which can

substantially prevent the serious symptoms of this disorder.

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Gor those families with a history of the disorder, a doctor can

determine durin a womanDs prenancy whether her baby has

alactosemia :6; by takin a sample of fluid from around the fetus

:amniocentesis;, or :>; by takin a sample of fetal cells from the placenta :chorionic villus samplin or 1K!;.

Galactosemia treatment

The only way to treat alactosemia is throuh dietary restrictions.

%eople with the disorder must stay away from foods and drinks

containin alactose, includin milk, cheese, and leumes :dried

beans;.

Multi1le-Gene

8enetic disorders may also be comple', multifactorial, or polyenic,

meanin they are likely associated with the effects of multiple enesin combination with lifestyles and environmental factors.

$ultifactorial disorders include heart disease and diabetes. )lthouh

comple' disorders often cluster in families, they do not have a clear3

cut pattern of inheritance. This makes it difficult to determine a

person/s risk of inheritin or passin on these disorders. 1omple'

disorders are also difficult to study and treat, because the specific

factors that cause most of these disorders have not yet been identified.!tudies which aim to identify the cause of comple' disorders can use

several methodoloical approaches to determine enotype3phenotype

associations. (ne method, the enotype3first approach, starts by

identifyin enetic variants within patients and then determinin the

associated clinical manifestations. This is opposed to the more

traditional phenotype3first approach, and may identify causal factors

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that have previously been obscured by clinical heteroeneity,

penetrance, and e'pressivity.

(n a pediree, polyenic diseases do tend to "run in families", but the

inheritance does not fit simple patterns as with $endelian diseases.

9ut this does not mean that the enes cannot eventually be located

and studied. There is also a stron environmental component to many

of them :e.., blood pressure;.

&n some cases, people who are concerned that they miht carry certain

variant enes can have enetic testin so they can learn their

childrenDs chances of inheritin a disease. %reanant 2omen can alsohave tests done to see if the fetus they are carryin miht have certain

enetic illnesses. 8enetic testin usually involves takin a sample of

someoneDs blood, skin, or amniotic fluid and checkin it for enetic

chanes.

Al3heimer4s Disease

What is Alzheimer's disease?

)l=heimerDs is a disease that causes dementia, or loss of brain

function. &t affects the parts of the brain that are important for

memory, thouht, and lanuae.

The brain of a person with )l=heimerDs contains abnormal clumps of

cellular debris and protein :plaques; and collapsed microtubules

:support structures inside the cell;. $icrotubule collapse is caused by

a malfunctionin protein called tau, which normally stabali=es the

microtubules. &n )l=heimerDs patients, tau proteins instead cluster

toether to form disablin plaques and tanles. These plaques and

tanles damae the healthy cells around them, leadin to cell death.

The brain also produces smaller amounts of neurotransmitters

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:acetylcholine, serotonin, and norepinephrine;, chemicals that allow

nerve cells to talk to one another.

The most common form of the disease, which strikes after ae @, is

linked to the apolipoprotein < :apo<; ene on chromosome 6L.

!cientists donDt know how apo<C increases the risk of developin

)l=heimerDs. They do know that everyone has apo<, which comes in

three forms.

(ne of the forms :apo<C; increases a personDs risk of developin)l=heimerDs. The other two forms seem to protect aainst the disease.

2hile people who inherit the apo<C form of the ene are at increased

risk for the disease, they will not necessarily develop it.

$utations in enes found on chromosomes 6, 6C, and >6 are linked to

rarer forms of the disease, which strike earlier in life.

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Dianosis

ue to the wide rane of enetic disorders that are presently known,

dianosis of a enetic disorder is widely varied and dependent of the

disorder. $ost enetic disorders are dianosed at birth or durin early

childhood, however some, such as 7untintonDs disease, can escape

detection until the patient is well into adulthood.

The basic aspects of a enetic disorder rests on the inheritance of

enetic material. 2ith an in depth family history, it is possible to

anticipate possible disorders in children which direct medical

professionals to specific tests dependin on the disorder and allow

parents the chance to prepare for potential lifestyle chanes, anticipate

the possibility of stillbirth, or contemplate termination. %renatal

dianosis can detect the presence of characteristic abnormalities infetal development throuh ultrasound, or detect the presence of

characteristic substances via invasive procedures which involve

insertin probes or needles into the uterus such as in amniocentesis.

19



y1othyroidism

The thyroid is the larest endocrine land in the body. &t sits just

below the laryn' :voice bo'; and wraps around the trachea:windpipe;. The thyroid land produces thyroid hormone, which helps

the body row and develop. &t also plays an important role in the

bodyDs metabolism :the processes in the body that use enery, such as

eatin, breathin, and reulatin heat;.

7ypothyroidism :or underactive thyroid; is a common condition in

which the thyroid land makes too little thyroid hormone. )bout 6 in,555 babies is born with conenital hypothyroidism, in which the

thyroid fails to row normally and cannot produce enouh hormone.

There is no known cause for most cases of conenital

hypothyroidism. 9ut about 65 to >5 percent of the time, the condition

is caused by an inherited defect that alters the production of thyroid

hormone.

The most common inherited form of hypothyroidism is a defect of the

T%( :thyroid pero'idase; ene on chromosome >. This ene plays an

important role in thyroid hormone production.

20



H! d "e"le get h#"th#ridism?

7ypothyroidism may be caused by :6; an autoimmune disease that

attacks the thyroid land, :>; surery or radiation to treat thyroid

cancer and other conditions, or :A; rare and random enetic events inwhich a mutation is acquired durin early embryonic development.

S#m"tms $ h#"th#ridism

&n babies with the inherited form of hypothyroidism, the condition

affects rowth and conitive development. &t may cause intellectual

disability, delayed puberty, stunted rowth, and ata'ia :uncoordinated

muscle movements;.

&n adults, hypothyroidism slows the bodyDs metabolism, makin the patient feel mentally and physically sluish. !ymptoms may include

weakness, fatiue, muscle aches, mood swins, hair loss, memory

loss, or slow speech. ) personDs symptoms will depend upon how little

thyroid hormone they make, and for how lon they have had the

disorder.

21



2hen the body has too little thyroid hormone, the pituitary land

works overtime, makin e'tra thyroid3stimulatin hormone :T!7;.

7avin too much T!7 may enlare the thyroid, formin a oiter.

%iagnse

9abies are normally screened for hypothyroidism >C hours after birth.

) tiny sample of blood taken from the babyDs heel is tested for low

thyroid hormone levels or hih thyroid3stimulatin hormone :T!7;

levels.

H#"th#ridism treatement

7ypothyroidism is treated with hormone replacement therapy# people

with hypothyroidism must take a synthetic form of thyroid hormone

every day to reduce their symptoms. 2hen treatment is started riht

away, babies develop normally.

Treatment 5' Genetic Disorders

!ometimes scientists alter enes on purpose. Gor many years,

researchers have altered the enes in plants to produce other plants

with special characteristics, such as an increased resistance to disease

22



and pests or the ability to row in difficult environments. 2e call this

enetic enineerin.

The treatment of enetic disorders is an onoin battle with over 6M55

ene therapy clinical trials havin been completed, are onoin, or

have been approved worldwide. espite this, most treatment options

revolve around treatin the symptoms of the disorders in an attempt to

improve patient quality of life.

8ene therapy refers to a form of treatment where a healthy ene is

introduced to a patient. This should alleviate the defect caused by a

faulty ene or slow the proression of disease. ) major obstacle has

been the delivery of enes to the appropriate cell, tissue, and oran

affected by the disorder. 7ow does one introduce a ene into the

potentially trillions of cells which carry the defective copy4 This

question has been the roadblock between understandin the enetic

disorder and correctin the enetic disorder.

9ut there are problems with ene therapy. !cientists still donDt quiteknow what every ene in the human body does. 7ue scientific

efforts like The 7uman 8enome %roject and related projects have

completed a map of the entire human enome :all of the enetic

material on a livin thinDs chromosomes;, but it will take many more

years to find out what each ene does and how they interact with one

another. Gor most diseases, scientists donDt know if and how enes

play a role. %lus, there are major difficulties insertin the normalenes into the proper cells without causin problems for the rest of

the body.

There are also concerns that people miht try chanin enes for

ethically troublin reasons, such as to make smarter or more athletic

children. No one knows what the lon3term effects of that kind of

chane would be.

23



!till, for many people who have enetic diseases, ene therapy holds

the hope that they ? or their children ? will be able to live better,

healthier lives.

!onclusion

The last >5 years have seen reat technical advances in the analysis of

N) and the completion of the 7uman 8enome %roject in >55A.

These advances led to the discovery of which faulty enes cause

which of the many simply3inherited :$endelian; eneti diseases. This

knowlede has iven rise to reater understandin of the molecular

basis of many $endelian diseases, and why they have the inheritance pattern they do. !ome diseases are caused by a sinle faulty ene, but

do not follow a $endelian pattern of inheritance. Research into one of

these diseases, Graile E syndrome, revealed that a N) fault can

enlare over three enerations :a dynamic mutation; until a nearby

ene is silenced :switched off;. )nother disease, )nelman syndrome,

confirmed that some human enes are normally subject to enomic

imprintin, a phenomenon in which a ene is silenced dependin on

whether it was inherited from father or from mother. The molecular silencin process :N) methylation; involved in enomic imprintin

is a

classic e'ample of epienetic reulation, in which there is an endurin

chane in ene activity but without any chane in N) sequence.

<pienetic reulation underpins normal development from the

fertilised e to an embryo with its many different cell types and

orans, and may also be involved in response to early life

e'periences. Jnderstandin the role of numerous enetic variations

and epienetic reulation in common, multifactorial disorders 0 such

24



as diabetes, heart disease and cancer 0 is the focus of much current

research, and is provin to be a hue challene.

)dult health depends on a comple' interaction between inheritance,

nutrition and the physical andsocial environment throuhout prenatal

development and childhood.

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