moodle overviewof scd.97to2003 revised33008

AN INHERITED DISEASE THAT AFFECTS

THE RED BLOOD CELL

BY TINA E. COLEMAN, MPH

Overview of Sickle Cell Disease

What is sickle cell disease ?

Sickle Cell Disease:

It is an inherited disorder that affects the red blood cells.

You cannot catch sickle cell disease. You are born with it.

It is a life-threatening genetic disorder.

It is a life long disease that affects individuals from infancy through adulthood

People who have the disease have an abnormal or unusual form of hemoglobin in their blood

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Tina E. Coleman, MPH

Characteristics of sickle cell disease

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People with sickle cell disease can experience:

Chronic anemiaInfectionsFrequent episodes of pain (the hallmark of the disease)

StrokesDebilitating organ damageChronic (blood) transfusion therapyDeath at an early age

How common is sickle cell disease?

It is one of the most common genetic diseases in the U.S.

Approximately 50,000 – 90,000 persons in the United States have sickle cell disease.

Over 2 million persons carry the sickle gene

Sickle cell disease is more common than other genetic disorders such as:

Cystic fibrosis - affects about 30,000 persons in the US Hemophilia - affects about 18,000 persons in the US Muscular dystrophy - affects about 30,000 persons in the US

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Life Expectancy


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Life Expectancy for people who have sickle cell disease

Male – 42 years of age Female – 48 years of age

The disease can impact a person’s quality of life. Many person’s with sickle cell disease have severe organ damage in their adult years.

Who does sickle cell disease affect?

Sickle cell disease affects people of African ancestry - In America it commonly affects African Americas

In America it also affects people with ancestors from the Mediterranean sea area

Turkey Greece Italy

Saudi Arabia or Sub-Sahara Africans Spanish-speaking countries in southern and central America, and Cuba. The Caribbean India Middle East

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What are the rates for sickle cell disease by ethnic groups?

Sickle Cell Disease African Americas: 1 in 375 – 500 persons Hispanic/Latinos; 1 in 1,000 – 1,400 persons

Sickle Cell Trait African Americans: 1 in 14 persons Hispanic/Latinos: 1 in 100 persons

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Are there different types of hemoglobin?

Hemoglobin A or “normal hemoglobin” – is the usual type of hemoglobin

There are over 800 types of variant hemoglobins or hemoglobins different from hemoglobin A.

The hemoglobin variants can genetically match up with sickle hemoglobin to form what we call “sickle cell disease”.


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Are their different types of sickle cell disease ?

The term “Sickle Cell Disease” is an umbrella term for all the different types of sickle cell disease such as:

Sickle Cell Anemia (hemoglobin SS) Sickle C Disease (hemoglobin SC) Sickle E Disease (hemoglobin SE) Sickle Beta Thalassemia

The most common type of sickle cell disease is called

“Sickle Cell Anemia” or hemoglobin SS.

Sickle cell anemia is usually considered to have the most severe symptoms.


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How do you get sickle cell disease?

Sickle cell disease is an inherited condition.

In sickle cell anemia (the most common form of the disease)

Two (2) genes for sickle hemoglobin must be inherited

A person must inherit one sickle gene from each parent in order to have the sickle cell anemia or hemoglobin SS.

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How do you inherit the sickle cell gene?


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There are 46 pairs of chromosomes in the human body

Genes that carry your genetic make up (DNA) are located on the chromosomes

46 pairs of chromosomes

Genes are messengers


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Over 100,000 genes are distributed over 46 pairs of chromosomes.

This represents a gene. A gene carries messages (DNA)

So what are genes?


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Genes carry the messages that determines the characteristics that you will inherit.

For example: It is a gene that carries the message for the shape of your nose or the color of your eyes.

But it takes a pair of genes, one from your mother and one from your father, that ultimately determines the color of your eyes or the shape of your nose.

Genes determine your hemoglobin type


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What determines your hemoglobin type is also based on the genes

you inherit from your parents.

A person needs 2 genes, one from each parent, to determine what type of hemoglobin will be inherited.

Will a baby have normal hemoglobin, sickle cell trait or sickle

cell disease?

The 2 genes you inherit determine your hemoglobin type.

How are your hemoglobin genes affected?


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Your hemoglobin type is governed by your genes.

Sickle cell disease is caused by a genetic defect or mutation to the hemoglobin gene on the 11th chromosome.

What is sickle cell trait?

Sickle cell trait is not a disease.

A person who has sickle cell trait carries one gene for sickle hemoglobin (hg S) which could be passed on to his or her offspring and one gene for normal hemoglobin (hg A).

Persons with sickle cell trait can pass that gene (or genetic makeup “DNA”) on to their offspring.

Persons with sickle cell trait are the “carrier” of the gene.

Persons with sickle cell trait do not have the disease.

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Other things you need to know about sickle cell trait


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Sickle cell trait produces no symptoms or problems for most people.

Under unusual circumstances some people with sickle cell trait have had experiences with:

Blood in the urine (hematuria)

Urinary tract infections in pregnancy

Problems with their spleen in circumstances with low oxygen such as high altitudes or scuba divining or dehydration (not enough water in body).

What causes people to have medical problems ?


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The underlying problem in sickle cell disease involves the red blood cell.

The Red Blood Cell


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The normal red blood cell is round, plump and can easily change its shape and squeeze through tiny blood vessels.

Inside the red blood cell is a protein that is responsible for carrying oxygen to the tissues in your body.

It is also the protein pigment that makes the blood cell the color red.

The Red Blood Cell (cont.)


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The normal red blood cell lives for approximately 120 days.

The sickle red blood cell


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In a person with sickle cell disease, the red blood cell contains a different type of hemoglobin which is called sickle hemoglobin.

When a red blood cell with sickle hemoglobin gives up its oxygen it collapses into a half moon shape or sickle shape cell.

The sickle red blood cell goes through the process of releasing its oxygen several times and forms and reforms itself until its shape becomes totally distorted and finally taken out by the spleen.

Note the different distorted shapes of cells with sickle hemoglobin

The sickle shaped red blood cell (cont. 1)


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The substance in the red blood cell with sickle hemoglobin is very sticky and causes the red blood cells to become rigid and sticky and clump together.

This clumping together of red blood cells in the blood vessels causes crippling episodes of pain and damage to vital organs.

This sticky, hard, substance in the red blood cell is what causes most of the problems for people with sickle cell disease.

Red blood cells clumping and sticking together is called vaso-occlusion

The sickle shaped red blood cell (cont. 2)


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The normal red blood cell lives 120 days.

The sickle cell only lives approximately 10-20 days.

This decrease in red blood cells in the body is what causes anemia in sickle cell disease.

The body is constantly working to produce more new red blood cells.

What will be covered in the other units?

An introduction to patterns of inheritance and genetic probabilities

Further exploration into sickle cell disease and hemoglobin variants with a discussion on qualitative and quantitative hemoglobin variants as related to sickle cell disease.

Introduction to the pathophysiology of sickle cell disease – the how and why sickle cell disease damages the body.

Introduction to the common medical manifestations and treatments for sickle cell disease.

Introduction to laboratory testing for the diagnosis of sickle cell disease.

Introduction to newborn screening for sickle cell disease.


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moodle overviewof scd.97to2003 revised33008

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