What is thalassemia? | types of thalassemia |

What is thalassemia?

Definition:
the thalassemia syndrome is a heterogeneous group of inherited anemias characterized by the defects in the synthesis of one or more globin chain subunits of the hemoglobin tetramer.

OR

Reduced rate of normal hemoglobin production due to the reduction or absence of the globin chains of hemoglobin.

Brief history of thalassemia:

The word thalassemia derived form Greek word " thalas" which mean "sea" and "emia" which means "blood".
This disease was first diagnosed in people from the Italian Greek coasts and nearby Mediterranean sea.
It was well-established fact that thalassemia is widely distributed all over the world. In 1925 two American pediatricians, Thomas Cooley and Lee first described thalassemia (beta) as a diseases characterized by the severe anemia, splenomegaly(spleen enlargement) and bone deformities.

Classification/types of thalassemia:

the thalassemia has been classified mainly into alpha and beta thalassemia but other classification for thalassemia is below

1. Classification on the basis of globin chains:

On the basis of the globin chains the thalassemia has been classified into the following types;

1. Alpha thalassemia
2. Beta thalassemia 
3. δβ (Delta, beta) thalassemia  
4. γβ (gamma, beta) thalassemia
5. Hbs thalassemia
6. HbE thalassemia
7. HbD thalassemia
   

2. Classification on the basis of severity:

On the basis of clinical severity of the diseases thalassemia has been classified into the following types;

A) Alpha thalassemia:

• Silent alpha thalassemia
• Alpha thalassemia trait/ alpha thalassemia minor
• HbH disease
• Hydrops fetalis/Hb barts

B) Beta thalassemia:

• Beta thalassemia minor
• Beta thalassemia intermedia
• Beta thalassemia major

3. Molecular based classification of thalassemia:

A) Alpha thalassemia:

• α0 (alpha not) shows the two alpha genes removal or mutated. for  example α thalassemia trait
• α+ shows one alpha gene removal or mutated. for example silent carrier 
  

B) Beta thalassemia:

• β0 (beta not) shows one complete removal of beta gene.
  
• β+ shows the diminished or reduce amount of beta genes
  

Genetic polymorphism of alpha thalassemia:

Clinical nomenclature	Genetic defect	Genotype
Silent carrier	One gene deletion	αα/- α
α‐thalassemia trait	Two gene deletion	- α /- α,  ../ αα
Hb-H disease	Three gene deletion	α-/...
Hydrops fetailis	Four gene deletion	../..

Genetic polymorphism of beta thalassemia:

Genotype	Genetic   description	Phenotype
β0/β0	Homozygous	Major
β+/β+	Homozygous	Major or intermedia
β0/ β +	Heterozygous	Major or intermedia
β0/ β	Heterozygous	Intermedia or minor
β+/ β	Heterozygous	Minor

Here the phenotype major intermedia is two times but first one is homozygous and second one is heterozygous.
Currently more than 400 beta gne mutations have been identified but among these 400 mutations only 5 of theme usually account for more than 90% of the cases of β thalassemia in the world.

in the united states two thalassemia are the most common one which is the intermedia and major, and more than million people have intermedia.
In Pakistan the most common type of thalassemia is beta thalassemia.