**2. Classification of β-thalassemias**

#### **1. β-Thalassemia**

	- **•** HbC/β-thalassemia
	- **•** HbE/β-thalassemia
	- **•** HbS/β-thalassemia
	- **•** β-Thalassemia-trichothiodystrophy
	- **•** X-linked thrombocytopenia with thalassemia

#### **2.1. Epidemiology of β-thalassemias**

The frequency of β-thalassemia varies widely, depending on the ethnic population. The disease is reported most commonly in Mediterranean, African, and Southeast Asian populations. The highest carrier frequency is reported in Cyprus (14%), Sardinia (10.3%), and Southeast Asia [1].

Population migration and intermarriage between different ethnicities have introduced thalassemia in almost every country of the world, including Northern Europe, where thalassemia was previously absent [2].

About 1.5% of the global population (80–90 million) are β-thalassemia carriers, with about 60,000 symptomatic individuals born annually. Incidence of symptomatic individuals is estimated at 1 in 100,000 worldwide and 1 in 10,000 in Europe [2].

It is the most common chronic hemolytic anemia in Egypt (85.1%), and its carrier rate has been estimated at 9–10.2% from an examination of 1000 normal random subjects from different geographic areas of the country [3].

#### **2.2. Etiology of β-thalassemia**

β-globin gene maps in the short arm of chromosome 11, in a region that contains also the delta globin gene, the embryonic epsilon gene, the fetal gamma genes, and a pseudogene (ψB1) [1].

114 Epidemiology of Communicable and Non-Communicable Diseases - Attributes of Lifestyle and Nature on Humankind

Unlike the deletions that constitute most of the α-thalassemia syndromes, β-thalassemias are caused by hundreds of mutations that affect all aspects of β-globin production: transcription,

The frequency of β-thalassemia varies widely, depending on the ethnic population. The disease is reported most commonly in Mediterranean, African, and Southeast Asian populations. The highest carrier frequency is reported in Cyprus (14%), Sardinia (10.3%), and Southeast Asia [1].

Population migration and intermarriage between different ethnicities have introduced thalassemia in almost every country of the world, including Northern Europe, where thalas-

About 1.5% of the global population (80–90 million) are β-thalassemia carriers, with about 60,000 symptomatic individuals born annually. Incidence of symptomatic individuals is

translation, and the stability of the β-globin product [2].

**2. Classification of β-thalassemias**

**1. β-Thalassemia**

**•** Thalassemia major

**•** Thalassemia minor

**•** HbC/β-thalassemia

**•** HbE/β-thalassemia

**•** HbS/β-thalassemia

**•** Thalassemia intermediate

**2. β-Thalassemia with associated Hb anomalies**

**4. Autosomal dominant forms of β-thalassemia**

**•** β-Thalassemia-trichothiodystrophy

**2.1. Epidemiology of β-thalassemias**

semia was previously absent [2].

**3. Hereditary persistence of fetal Hb and β-thalassemia**

**5. β-Thalassemia associated with other manifestations**

**•** X-linked thrombocytopenia with thalassemia

estimated at 1 in 100,000 worldwide and 1 in 10,000 in Europe [2].

β-Thalassemia is inherited as an autosomal recessive disorder. There are hundreds of mutations within the β-globin gene, but approximately 20 different alleles comprise 80% of the mutations found worldwide. Within each geographic population, there are unique mutations. The large majority of mutations are point mutations. Deletions of β-globin gene are uncommon. Mutations in β-globin gene cause a reduced or absent production of the β-globin chains [4]. **Table 1** displays the list of common mutations according to severity and ethnic distribution.


**Table 1.** Common mutations of β-thalassemia according to severity and ethnicity.
