HLA Typing and matching

This Is Why HLA Typing Is Very Important For Organ & Tissue Transplants


Nikhil (name changed), a 10 year old boy was diagnosed with Beta Thalassemia Major – a severe form of blood disorder. As the days passed by, his health started deteriorating at a fast pace. However, according to the doctors there was a ray of hope – Neeraj, his 7 year old brother.  His umbilical cord blood was harvested and saved after his birth and that meant Nikhil’s chance of survival. Presently, cell-stem transplant is the only cure for B-Thal major.

To match the compatibility of the donor and the receiver, HLA Typing is necessary. After the typing, the compatibility was matched. After a successful transplant, Nikhil made a recovery and now shows no signs of B-Thal.

About HLA

HLA (human leukocyte antigen) is a protein or marker – found on cells in human body. Immune system uses HLA markers to know which cells belong in our body & which don’t. Its main use is in organ and tissue transplant treatments. It checks if receiver and donor are compatible.

For example, in bone marrow transplant, HLA genes and antigens of donor and the recipient should be same or match closely for a transplant to be successful. Otherwise the donor’s tissue may get attacked or rejected by the recipient’s immune system.

HLA testing and matching
Image credits- bethematch.org

What is HLA Typing?

A high-resolution typing result is defined as a set of alleles that encode  the  same  protein  sequence  for  the  region  of  the  HLA molecule called the antigen binding site and that exclude alleles that are not expressed as cell-surface proteins.

Every person (except identical twins) has different sets of HLA alleles. Transplanted organs are allografts, in which the donor organ and the recipient are genetically different. Compatibility (matching) of the HLA of the donor and the recipient increases the chance for a successful engraftment. Matching is determined by comparing alleles. Resolution is the level of detail with which an allele is determined. The MHC is a polymorphic locus encoding the HLA genes.

Antigens encoded by the HLA genes are responsible for allograft tissue and organ rejection. Identifying and matching alleles increases the chance of successful organ and tissue transplant. These antigens help the body’s immune system distinguish which cells are “self” and which are “foreign” or “non-self.” Any cells that are recognized as “non-self” can trigger an immune response, including the production of antibodies.

Different kinds of transplants necessitate different levels of matching between donor and intended recipient. This may determine which HLA tests are performed and which HLA genes are tested for.

HLA antigens and their corresponding sequence alleles are determined by serological- and DNA- based methods.

Why is it necessary?

Determination of HLA alleles by DNA typing techniques is necessary for HLA matching of donor and recipient at transplantation, medical research of HLA-related diseases and individual identification including paternity testing.

This testing also includes screening transplant recipients for the presence of antibodies that might target the donated tissue or organ as part of an immune response.

HLA mis­matches found using very sensitive tissue-typing methods — methods known as “high-resolution” typing — can have just as significant an impact on trans­plant outcomes as mis­matches found using “low-resolution” methods.

High-resolution typing is important for ensuring the best possible match between donor and recipient because a match suggested by Low Resolution HLA Typing is generally only 56% accurate.

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Genetic Testing and Beta Thalassemia


When a year old Moinam’s parents noticed his pale appearance and tiredness, they consulted a physician near their home in Siliguri. His blood test showed alarmingly low hemoglobin count. But the doctor prescribed an iron-based tonic without concluding, thinking that he was suffering from a minor form of anemia.

However, later it was discovered that he had beta-thalassemia. Until he was recommended for stem-cell transplantation, he had to continuously undergo regular medication and blood transfusion.

After the stem-cell transplantation, his blood tests started showing positive results and his parents; who are carriers of thalassemia, were relived.

Just like Moinam, around 10,000 to 12,000 babies with major thalassemia syndrome are born each year in India.

It has been estimated that there are around 30 to 40 million carriers of beta-thalassemia in the country. In spite such alarming numbers, very little is known about this disease.

Because of the complexities, thalassemia is considered as a dreadful disease. However, isn’t it surprising that bollywood superstar Amitabh Bachchan also has thalassemia minor yet perfectly leading a normal life and continues to entertain us?

About Beta-thalassemia

Beta-thalassemia is a blood disorder that causes decreased production of hemoglobin, a molecule that carries oxygen throughout the body.

People with a mutation only in one copy of gene have thalassemia minor. Thalassemia minor results in zero or very slight anemia.

Thalassemia major occurs when child acquires two mutated genes, one from each parent.  Children born with thalassemia major usually develop the symptoms of severe anemia within the first year of life.

Beta-thalassemia is most common in African American, Asian, Hispanic, Mediterranean and Middle Eastern populations than other populations.

Effects

Reduced amounts of hemoglobin cause a shortage of red blood cells, called anemia. Severe anemia can cause a person to be pale, short of breath, easily tired, and have poor growth. Frequent infections and blood clots are also associated with anemia. The severe type of beta-thalassemia, called Cooley’s anemia, or beta-thalassemia major, causes life-threatening anemia, failure to thrive, poor growth, jaundice, and enlarged organs including the liver, spleen, and heart.

How it is inherited?

Beta-thalassemia is an autosomal recessive disorder, which means that a couple might have a child with beta-thalassemia only if both reproductive partners are carriers. When both reproductive partners are carriers of beta-thalassemia, there is a 25% chance of each child having the disease.

Beta Thalassemia inheritance

 

Genetic testing helps.

There are two tests available for testing if you’re either a carrier or a beta-thalassemia major:

  1. Complete Beta thalassemia (HBB) gene analysis:

This test analyzes the HBB gene for all the mutations that may cause Beta-Thalassemia, by Sanger sequencing.

2. Genetics Screening for Beta Thalassemia                    (5 common mutations):

 This test analyzes the 5 most common mutations in the HBB gene that may cause Beta-Thalassemia, by Sanger sequencing. These common mutations are the most common ones found in 90% of Indian population. Both of the above tests require a sample of 4 ml whole blood.

The results–

If you are a carrier of beta-thalassemia, the next step is to have your partner tested to check if she/he is a carrier too.
If your partner is tested and is not a carrier then the chance of the two of you having a child with beta-thalassemia is low. Speak with your doctor or genetic counselor for recommended next steps.
If your partner is tested and you both are carriers of beta-thalassemia, then there is a 25% chance that each child will have beta-thalassemia. This chance is the same regardless of your ethnic background or your family history.

Since beta-thalassemia is an inherited disease, your close family members are at increased risk of being carriers as well. It will be better for them if they get tested too.

What are the treatments?

 Treatment for beta-thalassemia includes regular blood transfusions. In some cases, a stem cell transplant can cure the disease. This is necessary to provide a temporary supply of healthy red blood cells with normal hemoglobin that the patient’s body needs. Nowadays, drugs designed to remove excess iron (iron chelators) have significantly changed the prognosis of thalassemia.

Apart from proper medication and keeping check on iron content in diet (as the iron overload may cause complications with major organs), a typical day in a life of child with beta-thalassemia is pretty normal.

Thus, medical advances continue and promise to improve the life expectancy and quality of life further for those living with thalassemia.

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