THIS is apropos of a news report, ‘Thalassaemia test may become mandatory in Islamabad’ (May 28). Thalassaemia is a blood disorder inherited from parents and makes an abnormal form of haemoglobin: the protein in red blood cells that carries oxygen.
The disorder results in excessive destruction of red blood cells, leading to anemia. Haemoglobin is made of two proteins:
Alpha and Beta globins, and ensuing thalassaemia is separated into two major types: Alpha and Beta thalassaemia.
Thalassaemia occurs when there is a defect in a gene that helps control production of one of these proteins. Alpha thalassaemia occurs when a gene or genes related to the alpha globin protein are missing or changed (mutated).
Beta thalassemia occurs when similar gene’s defects affect production of beta globin protein. Alpha thalassaemia occurs most commonly in persons from Southeast Asia.
The deficit in alpha globin results in decreased assembly of the Alpha2 and beta2 haemoglobin tetramers, the accumulation of unstable beta4 tetramers, and a consequent microcytic, hypochromic, haemolytic anemia.
The molecular basis of alpha thalassaemia is most commonly a deletion of one or both of the two alpha globin genes located in adjacent positions on the short arm of chromosome.
These single and double gene deletions result, respectively, in the partial or complete loss of alpha globin synthesis from the affected chromosome.
The specific size and position of the alpha globin gene deletion differs among populations. The molecular defect predicts the total loss of expression of the affected alpha2-globin gene and suggests a basis for its unusually severe effect upon overall a-globin synthesis.
Beta thalassemia is also of public health importance in many parts of the world, including Pakistan. Screening for â-thalassaemia trait (BTT) is necessary for family counselling.
Carriers of beta- thalassaemia trait (BIT) can have varying degrees of anemia. Some of them have no symptoms and, therefore, can be detected only in a population survey or as a part of family study, if other members are symptomatic or have thalassaemia major.
http://www.jpgmonline.com/article.asp?issn=0022-3859;year=1982;volume=28;issue=1;spage=4;epage=8;aulast=Agarwal - ref6Raised Hb-A2 has been accepted as a reliable criterion for the diagnosis of BTT.
Pre-marital tests for both major types of thalassaemia are very important in a population where close marriages are not uncommon. These tests can save lots of lives which are supposed to suffer from genetical disorders after getting the birth if both their parents had genetic makeup atypical.
Conversely, there is a need to understand how to get accurate results from labs which could correctly differentiate between major and minor types of thalassaemia. Severity of thalassaemia depends upon the number of genes affected in both parents.
Inheriting defective genes from both parents leads to development of thalassaemia major.
Thalassaemia minor usually occurs if someone receives the defective gene from only one parent, and this form of disorder-carrier usually does not have symptoms. Misled diagnosis of thalassaemia, and incorrect tests and its interpretation can be damaging and could cause a hindrance for couples from getting married.
HABIB HYDER LAGHARI Canada