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What is Sickle Cell

 
 

الزيارات : 78

التاريخ : 13-07-2006

 
 

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What is Sickle Cell

 

Most of our physical characteristics are inherited, through the genes we take from our parents, for example, the shape of our nose, colour of our skin and eyes we also inherit our haemoglobin (Hb) type from our parents, through the genes.

 

Haemoglobin (Hb) is the substance in the blood which gives it its red colour, it carries oxygen (air) around the body, therefore it is vital for maintaining life.  Without red blood cells the body cannot function

 

World wide the usual and most common adult haemoglobin type is known by the letter A.  Where a person has inherited haemoglobin A from both parent they will have the usual haemoglobin combination AA (Hb AA). In this instance the red blood cells are round, able to carry air (oxygen) well and they flow easily around the body (see diagram1).

 

A small proportion of people inherit unusual haemoglobins, for example, sickle haemoglobin.  There are approximately 400 unusual haemoglobins known in humans.

 

Some people inherit one usual adult haemoglobin from one parent and one sickle haemoglobin form the other and are said to have sickle cell trait (HbAs) these individuals have healthy red blood cells, they are not ill, they are well and do not have any symptoms.  It cannot change into any other type of haemoglobin later in life.

 

Sickle cell trait is very useful in those parts of the world.

 

Sickle cell trait is found in people whose ancestors originate from:

Asia, Africa, Mediterranean Island, Middle and Far East, and South America.  Because of migration it is also found in Caribbeans Black British, Black Americans and others whose ancestors came originally from parts of the world where sickle haemoglobin is common.

 

 

Those who have sickle cell trait, They are perfectly healthy and do not have a disease or illness.

 

In fact many athletic people have sickle cell trait and it dose not affect their physical performance in any way.

 

The red blood cells of people with sickle cell trait (HbAs) remain round and carry oxygen (air) normally.  Because there are no symptoms associated with sickle cell trait these individuals will not know that they carry this unusual haemogolobin, unless they have had a special blood test, or they have a child with someone who also has an unusual haemoglobin and their child is born with a sickle cell syndrome.

 

For a couple who BOTH have sickle cell trait (HbAs), EACH time they are expecting a child there is a 1 in 4 chance, that their child could inherit sickle cell anaemia (Ab SS), which is one of the sickle cell syndromes.

 

WHAT ARE SICKLE CELL SYNDROMES?

 

Sickle cell syndromes, sometimes abbreviated as (SCS), are commonly called sickle cell ‘diseases'.  For the purpose of this leaflet the term ‘syndromes' will be used.  Sickle cell syndromes (SCS) are genetically inherited conditions which affect the red blood cells haemoglobin.

 

If a person inherits two sickle haemoglobins, one from each parent, they will have condition called sickle cell anaemia (HbSS).  Where the sickle haemoglobin is inherited with another unusual haemoglobin, for example, haemoglobin C, the individual will have sickle haemoglobin C syndromes (Hb Sc).  If sickle is inherited with beta thalassaemia the individual will have sickle beta thalassaemia syndrome (Hb SBThal).

 

These are just three types of the condition known collectively as sickle cell syndromes.  Sickle cell anemia (Hb SS) is the most common and often the most severe of the three.

 

In these conditions the red blood cells lose their ability to carry oxygen properly, the cells become hard, brittle, fragile, break easily and only live half as long as healthy red blood cells clog together and block the narrow blood vessels, this gives rise to a severe pain known as ‘sickle cell crisis'.

 

People with sickle cell syndromes may experience tiredness, feel lethargic, lose their appetite; they are prone to getting infections and will often become breathless during strenuous exercise.

 

During a crisis a person may need to be admitted to hospital for treatment of infection or for relief of pain.  Although, these episodes are not constant they are unpredictable in onset and severity.

 

How is a sickle cell syndrome treated?

 

There is no simple cure for sickle cell syndromes; doctors treat the symptoms, if and when they occur.  Individuals with this condition can do a lot to prevent symptoms by, learning as much as they can about the condition and taking steps to stay healthy.

 

For example, avoiding damp cold conditions, taking prescribed medicines, eating a healthy balance diet, avoiding smoking, and by seeking prompt medical care when required.  Because the anaemia is not caused by lack of iron, it is important that iron tablets or iron tonics are Not taken, unless it is prescribed by a doctor.

 

So what is the difference between sickle cell trait and a sickle cell syndrome?

 

Sickle cell trait (Hb As) is not a disease or an illness.  Because these individuals have one usual haemoglobin A, their red blood cells remain round and healthy.  They just carry the unusual sickle haemoglobin gene.

 

Sickle cell syndrome on the other hand can be a serious condition, even though it can affect individuals differently.  While some people remain fairly well, others may experience many episodes of pain and discomfort which require hospitalization.

 

How do you get a sickle cell syndrome?

 

A person can only get sickle cell trait, or a sickle cell syndrome, from their parents.  These conditions cannot be transmitted like an infection, they can only be inherited through the genes.

 

Here is how it works.  Each parent is born with two haemoglobin genes.  Each time a couple are expecting a child, the child will take one haemoglobin gene from each parent, to be able to make their own two haemoglobin genes.

 

In each pregnancy there are always four possible combinations the child can take, these are known as chances.

 

Here are a few examples:

 

Example 1

 

If both parent have the usual, most common combination of haemoglobin (Hb AA)

 

This couple's children have a 100% chance of inheriting the usual combination of haemoglobins.  None of their children will inherit any unusual haemoglobin

 

Example 2

 

If one parent has the usual combination of haemoglobin (Hb AA) and the other parent has one usual and one unusual sickle haemoglobin combined, thus having sickle cell trait (Hb AS).

 

This couple's children have a 50% chance of inheriting the usual combination of haemoglobin (Hb AA) or a 50% chance of inheriting sickle cell trait (Hb As), like one of the parents.  This couples children cannot inherit a sickle cell syndrome.

 

Example 3

 

If both parents have one usual haemoglobin and one unusual sickle haemoglobin combined, this means both of them have sickle cell trait (Hb As) this couple's children have a 25% chance of inheriting the usual combination of haemoglobin (Hb AA), a 50% chance of inheriting sickle cell trait (Hb As), like the parents, or a 25% chance of inheriting sickle cell anaemia (Hb SS).

 

These are only a few examples.  It is possible to inherit one sickle haemoglobin from one parent and another unusual haemoglobin type from the other parent, if that parent also carry an unusual haemoglobin.  Therefore there is still a risk that their child can inherit a sickle cell syndrome.

 

Because there are so many unusual haemoglobins it is not possible to give every type of combination in this short leaflet.

 

But remember it all depends on which heamoglobin your children take from you and your partner.  It is like a family tree.

 

Why should I get tested?

 

If you wish to find out about your haemoglobin type you can get tested.  But it is important, especially when you are planning to have children, or if you need to have an operation where anesthetic is required.

 

Talk to your GP, health visitor, school nurse, family planning nurse, social worker or any health care professional..

 

It is a simple blood test, which takes only a few minutes and you get the result in a few days.  Your GP can take blood for testing or arrange for it to be done at your local hospital.

 

Once you know the exact type of haemoglobin you and your partner have then you, your, GP, nurse or specialist counsellor can work out exactly which haemoglobin type your children could inherit from both of you.

 

What if we both have sickle cell trait and we want to have baby?

 

Since you and your partner have sickle cell Trait you have the following options:

 

Wait until the baby is born to find out what haemoglobin gene the baby has inherited from both of you.

 

Have the baby tested in the womb in early pregnancy.

 

 

Testing the baby in the womb is called PRE-NATAL diagnosis and can be done as early as ten weeks of pregnancy, in most cases.  The test is done in a hospital.  The result is usually available within 2-14  days.  This depends on the type of test you are offered.

 

You can discuss the various options with your GP, Midwife, hospital doctor or specialist .  They will be able to give you more information, advice and support to help you and your partner reach a decision.

 

 

Reference:

 Brochure from: London Sickle Cell/Thalassaemia Center, UK

 
     
 

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