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06/07/2020 By AskAwayHealth

Haemoglobin C Disease : Which is worse – SC or SS genotype?

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Haemoglobin C disease - african lady in blue deim coat and jacket with cornrows reading a book in a park.

Haemoglobin C disease: Which is worse – SC or SS genotype? There are several varieties of abnormal haemoglobin disease so this is a fair question. People with either condition should be treated as individuals but in this article, we highlight what makes them different even though they share the abnormal S gene.



Let’s look at another type of inherited abnormal haemoglobin disease – Haemoglobin C and how those with the condition are affected.

And it brings us to the question – who gets worse disease: people with Hb SS or Hb SC?

First, we are most familiar with Haemoglobin S, (Hb S).

It was the first abnormal haemoglobin discovered.

It is an abnormal type of haemoglobin protein, which causes sickling of the red blood cell.


How is Haemoglobin classified?

Haemoglobin is a protein of different chains whose chemical structure is controlled by our genes. 

But there are different types of haemoglobin. 

One way to identify them is a process called electrophoresis
in which electric current is used to separate the different parts of a substance.

And by identifying different molecules in particular haemoglobin types, we came up with Hb A, Hb C, Hb D, Hb E, Hb F and so on – named alphabetically in the order of discovery; except for S (named for the sickle shape).

Even among a haemoglobin type, there could still be structural differences. 

These are designated based on the city or location where they were first detected – so we have Hb C Harlem or Hb S Memphis.


How are Haemoglobin C and Haemoglobin S different?

Hb S is different from the normal Hb type – Hb A. 

The difference is one specific protein change between the two Hb types, A and S; and this is very similar to Hb C. 

So Hb S and Hb C are also different in the particular protein that makes up the chains in their structure.


What Are the Haemoglobin C conditions?

Haemoglobin C (Hb C) is one of the most common structural haemoglobin variants in the human population.

The inheritance of the Hb C gene is also similar to that of Hb S.

This means to have the Hb C gene, you have received the gene from one or both of your parents. 

Hb C is found in various populations in Africa, southern Europe, and South and Central America. 

Population studies suggest the highest occurrence of Hb C to be in Burkina Faso, West Africa.


1. Haemoglobin AC

If you inherit only one C gene and no other abnormal genes, then you have the Hb AC and are a haemoglobin C carrier or you have the trait.

Haemoglobin C carriers appear healthy, with no significant clinical abnormalities – just like those with the sickle carrier state (AS).

Some studies have suggested the AC genotype confers a protective effect from malaria (like AS) – but this is not conclusive as other studies did not show the same result.


2. Haemoglobin CC (Haemoglobin C disease).

This happens when a person inherits two copies of the abnormal C gene from each parent. 

Unlike those with the SS genotype, people with CC do not have severe disease. 

But they do form abnormal haemoglobin which also changes their red cells.

In this case, they have only a mild degree of red cell destruction and anaemia, so the clinical scenario is less complicated than sickle cell anaemia.


3. Haemoglobin S-C disease (Hb SC)

In this form of the disease, the individual has inherited BOTH an abnormal S gene from one parent; and an abnormal C gene from the other.

It is not an unusual development – for example if the parents are AS and AC; or they are SS and AC, or they are CC and SS etc.

This can, therefore, have significant consequences and parents in this category should have genetic counselling and guidance where available.

Research has found that the symptoms or illnesses associated with Haemoglobin SC disease are similar but less severe than those of Haemoglobin SS disease.

For example, the people with Hb SC have:

  • healthy growth and development – or just slightly less than expected compared to Hb SS.
  • The abnormal red cells in Hb SC can lead to situations where the blood vessels are blocked (crises) in the bones, or abdomen etc, but this is less frequent than in Hb SS disease.
  • some complications that could happen more in SC than SS
    • One of them is damage to the eye leading to loss of vision, and
    • the other is an injury to the hip joint – specifically damage to the bone after an interruption to the blood supply.
    • This commonly happens in the final stages of pregnancy.

Conclusion

Genotype testing is essential – not just for SS but for other haemoglobin abnormalities like SC which if co-inherited with the sickle gene may also lead to significant disease.

Learn about the treatments for Sickle Cell Anaemia – that is the people who inherit 2 abnormal S gene copies – understand the purpose of each medicine to how they help to promote health in people with SCA.

More Reading


References

Editing by AskAwayHealth Team

Disclaimer

All AskAwayHealth articles are written by practising  Medical Practitioners on a wide range of health care conditions to provide evidence-based guidance and to help promote quality health care. The advice in our material is not meant to replace the management of your specific condition by a qualified health care practitioner.
To discuss your condition, please contact a health practitioner or reach us directly

Image Credits: Photo by Gift Habeshaw on Unsplash

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