hgd -pillai aswathy viswanath

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TOPIC: HUMAN GENETIC DISORDERS By, Pillai Aswathy viswanath PG 1 Botany St. Thomas college kozhencherry

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Page 1: HGD -Pillai aswathy viswanath

TOPIC: HUMAN GENETIC DISORDERS

By,Pillai Aswathy viswanathPG 1 BotanySt. Thomas college kozhencherry

Page 2: HGD -Pillai aswathy viswanath

Introduction Gene is the unit for genetic information. Human being has about 30,000 genes Every gene has a different function, controlling all kinds of biological

activities including embryological development,

fetal growth, metabolism, personality,

cognition

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They are located on DNA strands which make up the chromosomes.

Chromosomes are the genetic material

within a cell nucleus.

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Genetic disorder A genetic disease or disorder is the

result of changes, or mutations, in an individual’s DNA

A mutation is a change in the letters (DNA sequence) that make up a gene.

Most people have the concept that a genetic disease must be one that is transmitted from one generation to

the next.

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Actually this is not totally correct. In medicine, a genetic disease refers to

one that is caused by abnormalities of the genetic material at the stage of germ

cell or early embryo. So genetic disorder is an illness caused

by one or more abnormalities in the genome, especially a condition that is present from birth (congenital).

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Each cell in the human body contains 23 pairs of chromosomes

The normal human chromosome complement consists of 46 chromosomes comprising 22

morphologically different pairs of autosomes and one pair of sex chromosomes.

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Each chromosome is made up of many genes

These genes make all the proteins in the body, which promote development and growth, and carry out all body functions.

When one or more of these genes or chromosomes are missing or mutated, or if extra chromosomes are present, the proteins may not get made, may be made incorrectly, or too many may be made. 

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Any of these situations can cause abnormal development and growth and can result in a genetic disorders.

Sometimes these abnormal genes or chromosomes are passed down from a parent, and sometimes they occur spontaneously without reason.

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Genetic disorder can be divided into three categories:

Single gene

disorders

. Chromoso

mal disorders

Complex disorder

s

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Single-gene disorders, where a mutation affects one gene.

Chromosomal disorders, where chromosomes (or parts of chromosomes) are missing or changed.

Complex disorders, where there are mutations in two or more genes. Often your lifestyle and environment also play a role.

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Examples of Genetic Disorders

Down Syndrome Edward Syndrome Patau Syndrome Klinefelter Syndrome Turner Syndrome Sickle Cell Disease

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Haemophilia Color Blindness Cystic Fibrosis Huntington’s disease Chronic myelogenous

leukemia Lesch-Nyhan syndrome

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Down Syndrome It is an autosomal

abnormality due to one extra chromosome in the 21st pair of autosome.

Hence this syndrome is called trisomy-21

Patients will have 47 chromosomes instead of 46 chromosomes.

They resemble to Mongolian

Also known as mongolism

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Down’s Syndromeor Trisomy 21

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Symptoms of Down Syndrome

Upward slant to eyes. Small ears that fold over at the top. Small, flattened nose. Small mouth, making tongue appear

large. Short neck. Small hands with short fingers. Low muscle tone.

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Looseness of joints. Small skin folds at the

inner corners of the eyes.

Excessive space between first and second toe.

In addition, down syndrome always involves some degree of mental retardation, from mild to severe.

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Edward Syndrome Edwards syndrome is a chromosomal

abnormality characterized by the presence of an extra copy of genetic material on the 18th chromosome, either in whole (trisomy 18) or in part 

It is named after John Hilton Edwards, who first described the syndrome in 1960.

 It is the second most common autosomal trisomy, after Down syndrome, that carries to term.

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Symptoms

Mental and physical retardation

Skull and facial abnormalities

Defects in all organ systems

Poor muscle toneAverage life

expectancy: 2-4 month

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Patau Syndrome Patau's syndrome is the

result of trisomy 13, meaning each cell in the body has three copies of chromosome 13 instead of the usual two.

Most cases of Patau syndrome are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm).

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Symptoms Individuals with trisomy

13 often have heart defects, brain or spinal cord abnormalities, very small or poorly developed eyes (microphthalmia), extra fingers or toes, an opening in the lip (a cleft lip) with or without an opening in the roof of the mouth (a cleft palate), and weak muscle tone (hypotonia).

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Due to the presence of several life-threatening medical problems, many infants with trisomy 13 die within their first days or weeks of life.

Only five percent to 10 percent of children with this condition live past their first year.

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Klinefelter Syndrome

This is the most common sex chromosomal abnormality

It was first identified in 1942 by klinefelter

Patients will have 47 chromosomes instead of 46 chromosomes.

That is 44 autosomes and 2X chromosomes along with a Y chromosomes

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Page 26: HGD -Pillai aswathy viswanath

Symptoms of Klinefleter’s syndrome

Phenotypically the patients are male but with rudimentary sex organs

They shows some feminine characters Development of breast tissue normally

seen in females. Little body hair is present, and such

person are typically tall, have small testes.

Infertility results from absent sperm. Evidence of mental retardation may or

may not be present.

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Turner Syndrome

It is a sex chromosomal abnormality in women.

first described in 1938 by Henry H Turner

The patients have only 45 chromosomes

Karyotype analysis shows that such females have 44 autosomes but they have only one X chromosomes

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Symptoms of Turner’s syndrome Turner syndrome is associated with

underdeveloped ovaries, short stature, webbed, and is only in women.

Bull neck, and broad chest. Individuals are sterile, and lack expected secondary sexual characteristics.

Absence of menstrual cycle Such women are prone to heart

diseases, hypothyroidism, diabetes and visual and auditory problems.

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Sickle cell anemia Sickle cell disease or sickle cell anemia is

a blood disorder Sickle cell anemia is one type of anemia. Anemia is a condition in which a person’s

blood has a lower than normal number of red blood cells, or the red blood cells don’t have enough hemoglobin.

Hemoglobin is an iron-rich protein that gives blood its red color and carries oxygen from the lungs to the rest of the body.

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A serious condition in which red blood cells can become sickle-shaped

Normal red blood cells are smooth and round. They move easily through blood vessels to carry oxygen to all parts of the body.

Sickle-shaped cells don’t move easily through blood. They’re stiff and sticky and tend to form clumps and get stuck in blood vessels.

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The clumps of sickle cell block blood flow in the blood vessels

Blocked blood vessel can cause pain, serious infection, and organ damage.

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Normal red blood cells live about 120 days in the bloodstream and then die.

In sickle cell anemia, the abnormal sickle cells usually die after only about 10 to 20 days.

The bone marrow can't make new red blood cells fast enough to replace the dying ones.

Sickle cell anemia is an inherited, lifelong disease. People who have the disease are born with it.

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If one parent has sickle cell anaemia (HbSS) and the other is completely unaffected (HbAA) then all the children will have sickle cell trait.

None will have sickle cell anemia.

The parent who has sickle cell anemia (HbSS) can only pass the sickle hemoglobin gene to each of their children.

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If both parents have sickle cell trait (HbAS) there is a one in four (25%) chance that any given child could be born with sickle cell anemia.

There is also a one in four chance that any given child could be completely unaffected.

There is a one in two (50%) chance that any given child will get the sickle cell trait.

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Haemophilia Haemophilia is commonly called bleeder’s diseases This is a recessive X-linked genetic disorder Lethal recessive genes located on the X

chromosomes bodies of individuals lose the ability to coagulate

blood or blood clotting. As the mutation is caused in X chromosome and the

condition is recessive, the females are carriers and males suffer from the symptoms of haemophilia.

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The most common type of hemophilia is called hemophilia A. This means the person does not have enough clotting factor VIII (factor eight).

A less common type is hemophilia B. This person does not have enough clotting factor IX (factor nine).

The result is the same for people with hemophilia A and B: they both bleed for a longer time than normal.

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Color Blindness Color blindness means

that you have trouble seeing red, green, or blue or a mix of these colors.

Color blindness is also called a color vision problem.

This disease consists of the inability to differentiate between reds and greens.

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Most color vision problems are

inherited (genetic) and are present at birth.

Colorblindness is caused by the X-linked gene.

Males are usually affected because they only need one X, where females need both.

Color blindness is caused by a defect in the retina or in other nerve portions of the eye

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People usually have three types of cone cells in the eye.

Each type senses either red, green, or blue light.

You see color when your cone cells sense different amounts of these three basic colors.

The highest concentration of cone cells are found in the macula, which is the central part of the retina 

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Inherited color blindness happens when you don't have one of these types of cone cells or they don't work right.

You may not see one of these three basic colors, or you may see a different shade of that color or a different color.

Weak green cone

Weak red cone

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symptoms of color vision problems

You may be able to see some colors but not others. For instance, you may not be able to tell the difference between some reds and greens but can see blue and yellow easily.

You may see many colors, so you may not know that you see color differently from others.

You may only be able to see a few shades of color, while most people can see thousands of colors.

In rare cases, some people see only black, white, and gray.

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Cystic Fibrosis Cystic fibrosis is an autosomal-recessive

genetic disorder It is caused by mutations in the CFTR (cystic fibrosis transmembrane regulator)

gene. The defective gene, CFTR, was identified in

1989 and mapped to the long arm of chromosome 7

The CFTR gene normally creates a protein that moves salt and water out of a cell.

If the CFTR gene is defective, it results in a build-up of thick, sticky mucus in the body's tubes and passageways.

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CF primarily affects the lungs and digestive system and makes a child more vulnerable to repeated lung infections. 

These thick secretions also obstruct the pancreas, preventing digestive enzymes from reaching the intestines to help break down and absorb food.

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symptoms of cystic fibrosis Abnormalities in the glands that

produce sweat and mucus, and may cause a loss of salt.This can cause imbalance of blood minerals, abnormal heart rhythms, and, possibly, shock.

Thick mucus in the lungs and intestines can cause malnutrition, poor growth, frequent respiratory infections, breathing difficulties, and/or lung disease.

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Sinusitis clubbing of fingers and toes - a

condition marked by the ends of the fingers and toes become enlarged; more prevalent in the fingers.

hemoptysis - coughing blood. cor pulmonale - enlargement of

right side of heart. abdominal pain gas in the intestines liver disease diabetes pancreatitis

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Huntington’s disease Huntington disease is a progressive

brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability

The disease is also known as Huntington's chorea. Chorea means "dance-like movements" and refers

to the uncontrolled motions often associated with the disease.

Having a parent with Huntington's is the risk factor.

A child of an affected parent has a 50% chance of inheriting the disease

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Mutations in the HTT gene cause Huntington disease.

The HTT gene provides instructions for making a protein called huntingtin.

Although the function of this protein is unknown, it appears to play an important role in nerve cells (neurons) in the brain.

The HTT mutation that causes Huntington disease involves a DNA segment known as a CAG trinucleotide repeat

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An increase in the size of the CAG segment leads to the production of an abnormally long version of the huntingtin protein.

The elongated protein is cut into smaller, toxic fragments that bind together and accumulate in neurons, disrupting the normal functions of these cells.

The dysfunction and eventual death of neurons in certain areas of the brain underlie the signs and symptoms of Huntington disease.

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Chronic myelogenous leukemia

Chronic myelogenous (or myeloid) leukemia (CML), also known as chronic granulocytic leukemia (CGL).

Chronic myeloid leukaemia (CML) is a type cancer that affects the blood and bone marrow.

In CML the bone marrow produces too many white cells, called granulocytes.

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More than 90% of cases are due to a gene abnormality caused when two chromosomes swap sections with each other.

There are 23 chromosomes in humans, and in patients with chronic myelogenous leukemia chromosomes 9 and 22 within blood cells exchange bits of genetic material to form a Philadelphia chromosome

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The new gene on this chromosome makes a protein called tyrosine kinase that allows white blood cells to grow out of control;

moreover, these abnormal white blood cells tend not to become old and die.

The bone marrow, where red blood cells, white blood cells, and platelets are made, becomes filled with white blood cells crowding out the normal cells and damaging the bone marrow itself.

This can impair the ability of the bone marrow to manufacture normal amounts of blood cells.

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Genetic Mutations Can occur as exposures to radiation,

chemicals, etc Known from 1981 or before that

Benzene (a byproduct of the use of laser printers and copy machines) caused the mutation leading to CML in humans

Not enough has been done to protect employees who work in the presence of Benzene

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symptoms Bone and joint pain may occur as the bone

marrow pressure increases due to an excess build-up of white blood cells.

Fatigue may be due to anemia because not enough red blood cells are being produced and bleeding can occur if not enough platelets are being manufactured.

In some patients with chronic myelogenous leukemia their bone marrow makes too many platelets and they can develop abnormal blood clotting, which can cause strokes.

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In chronic myelogenous leukemia there are too many white blood cells, but these white blood cells tend not to function properly and their ability to fight infection is compromised, which leads to an increased risk of infection.

The increased numbers of white blood cells spill out of the bone marrow and start circulating in the blood stream and eventually become trapped in the spleen, causing it to enlarge.

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Lesch-Nyhan syndrome It is an X-linked recessive disorder

which causes deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT).

Lack of HPRT leads to accumulation of uric acid in body, which leads to gout and kidney problems, poor muscle control and mental retardation of moderate degree.

A striking feature of this disorder is a child biting his lips and fingers.

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This self mutilating behavior appears in second year of a child's life.

Other than these features, an individual suffering from this disorder shows facial grimacing.

This disorder is alternatively also known as Nyhan's syndrome, Juvenile gout and Kelley-Seegmiller syndrome.

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Reference John B Jenkins (1990).Human Genetics Harper and Row,Publishers,New York http://www.buzzle.com/articles/genetic-

disorders-in-humans.html www.google.com, wikipedia.org http://www.diseaseinfosearch.org/ www.webmd.com/eye-health/tc/color-

blindness-topic-overview www.britannica.com/EBchecked/topic/

228874/human-genetic-disease

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By,Pillai Aswathy Viswanath