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Are you a thalassemia carrier? You could be. Find out why should you care?
Who is a carrier?
thalassemia carrier is someone that has a thalassemia mutation in one of the two genes involved in normal red blood cell production1. For a person to be thalassemic, s/he must have a defect on both genes. This thalassemia carrier state (of having a defect on only one of two genes) is also called thalassemia minor or thalassemia trait2 and causes no direct health problem. However when two carriers can have a child with severe thalassemia.
 
Prevalence of carriers? Are they that so many?
It is estimated that about 1.5% of the global population are carriers of beta-thalassemia, that’s about 106,455,000 people.2
 
Do carriers have the disease?
Carriers of the thalassemia trait do not have a disease. They have no physical or mental symptoms and do not require a special diet or medical treatment. The condition cannot become a serious disease over time, indeed, most will be unaware that they are carriers unless specifically tested. 2345
 
However, some carriers may experience mild anemia, which may be inaccurately diagnosed as iron deficiency anemia. Laboratory tests can easily differentiate between the two. 35
 
Carriers and pregnancy
Like any other woman, the carrier woman can normally conceive. However, she may need more iron supplements than usual during her pregnancy. 45
 
Can carriers donate blood?
Yes it is possible for carrier to donate blood if their hemoglobin (iron) level meets the international criteria for donation. 5
 
Can carriers donate stem cells / bone marrow?
Yes it is ok for carriers to donate stem cells, such as those in bone marrow, for his/her diseased sibling.
 
So, what is the problem?
The problem is that carriers could have thalassemia major children. In other words, when two carriers have a child, there is a 25% chance with each pregnancy, with a one to four, that the coming child will have thalassemia major. 6
 
Probabilities of having a thalassemia child
 
-When one parent is a carrier and the other is free, there will be no risk of having a child with B- thalassemia major. However, there will be probability to give birth to a carrier child by 50%.5 
 
-When both parents are carriers, for every pregnancy there is one in four (25%) chance that the child will have thalassemia major, one in two (50%) chance that the child will carry the thalassemia trait, and one in four (25%) chance that the child will be completely unaffected. 24
 
What should I do if I am a carrier?
I should be enrolled in thalassemia prevention programs.  Prevention programs will help me to avoid having a diseased baby with thalassemia major. 2
 
I have to tell my spouse to seek medical advice and get tested for thalassemia carrier status. I also have to notify my brothers and sisters that they could be carriers as well.5
 
Laboratory diagnosis of a carrier
 
-Blood picture
Carriers may show a degree of decreased hemoglobin levels (anemia) with reduced red blood cell size. 34
 
- Analysis of Hemoglobin (Hb) types and amounts:
-This is done by special tests, namely, Hb electrophoresis or HPLC.
-An elevated concentrations of a normal hemoglobin called HbA2 could be detected.12
 
-Detecting the thalassemia gene by PCR:
In which we are searching for the previously known thalassemia gene in the DNA of the carrier. 23
 
ß globin gene sequence analysis
It is a very efficient test (99% success). It is used when PCR didn't give us the desired result or in case of not knowing the gene of mutation that caused thalassemia.23
 
Prevention
Prevention of beta-thalassemia is based on carrier identification, genetic counseling and prenatal diagnosis.2
 
-Carrier screening and detection
Carrier detection has been previously described.
 
-Genetic counseling
It provides information for individuals and at risk couples (i.e. both carriers) regarding the mode of inheritance, the genetic risk of having affected children and the natural history of the disease including available treatments.2
 
-Prenatal diagnosis
Prenatal diagnosis for pregnancies at increased risk is possible by analysis of DNA extracted from fetal cells obtained by:
 
1- Amniocentesis: It usually performed at approximately 15th to 18th week of pregnancy by amniocenteses, which consists of taking a sample of the fluid surrounding the fetus which contains fetal cells.
 
2- Chorionic villi sampling: It is at 11 weeks of pregnancy, in this case a sample of placents is taken.2
 
-Preimplantation genetic diagnosis (PGD)
PGD also may be an option as well. 2 In PGD; thalassemia genetic testing is performed on embryos before being introduced in the mother’s womb.7
 
Detecting and educating carriers is the first step in achieving our goal of a thalassemia-free world.
 
Article by Dr Mohamed El Missiry, Cure2Children medical team
 
References:
 
1-Weatherall DG and Clegg JBThe thalassemia syndromes. 4th ed. Oxford, UK: Blackwell;2001.http://onlinelibrary.wiley.com/doi/10.1002/9780470015902.a0002274.pub2/full
2- Galanello R and Origa RBeta-thalassemia, Orphanet J Rare Dis, 2010; 5: 11. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2893117/?tool=pubmed
3- Cao A   and  Galanello R,  Beta thalassemia, 2000. http://www.ncbi.nlm.nih.gov/books/NBK1426/
4- Eleftheriou AAbout Thalassemia. Thalassemia International Publications (4). 2007.http://www.thalassaemia.org.cy/pdf/about_thalassaemia_EN_low.pdf
5- Eleftheriou A and Angastiniotis MAbout β- thalssemia. Thalassemia International Publications (11). 2007.http://www.thalassaemia.org.cy/pdf/b_thalassaemia_english.pdf
6- Cousens NEGaff CLMetcalfe SA, and Delatycki MBCarrier screening for Beta-thalassaemia: a review of international practiceEur J Hum Genet. 2010 October; 18(10): 1077–1083. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2987452/?tool=pubmed
7- Munné S and Wells DPreimplantation genetic diagnosis., Curr Opin Obstet Gynecol. 2002 Jun;14(3):239-44. Review.http://www.ncbi.nlm.nih.gov/pubmed/12032378

 

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