Table 1: Significant cases of SCDs including thalassemias by continent/region.

Continent/regionMajor disorderRemark/reference

Africa(1) SCA (HbSS)
(2) HbSC
(3) α-Thalassemia
HbC has lysine rather glutamine in 6th position as in β-globin of HbA
One in 12 Blacks worldwide carries the SCA trait. About 1 in 400 has SCA. About 75% of global SCAs are in Africa. About 150,000 SCA cases are born yearly in Nigeria. The carrier frequency ranges between 10% and 40% across equatorial Africa, decreasing to 1-2% in north Africa and <1% in South Africa [6].

Islands and countries in Mediterranean area and the Middle East(1) HbSβ 0 or β
(2) -Thalassemia
(3) -Thalassemia
(4) HbCβ 0 or β +  
(5) SCA
These islands and countries including Turkey have significant cases of SCDs and thalassemias. Saudi Arabia has a yearly rate of 3,000 newborns. Qatif City has the highest rate [7, 8].

America—USA(1) SCA
(2) -Thalassemia
(3) HbCβ 0 or β +  
(4) Other SCDs
About 72,000 persons in the US have SCA, mostly African-Americans at the rate of 1 in 500 newborns as against 1 in 1, 200 for Hispanic-American births [23, 24]. In 2004, 83,149 cases of hospitalization were attributed to SCD in the US at a cost of ~$488 million [9].

Asia(1) SCA
(2) α-thalassemia
(3) β-thalassemia
(4) HbCβ 0 or β +  
(5) HbEβ 0 or β +  
HbC has lysine rather glutamine in 26th position as in β-globin of HbA
SCA is significantly prevalent in Bangladesh, China, and other Asian countries. In India the prevalence ranges from 9.4 to 22.2%. Hemoglobin E/thalassemia is common in Cambodia, Thailand, and India. The Maldives has the highest incidence of thalassemias in the world with a carrier rate of 18%. The corresponding figures for Bangladesh, China, India, Malaysia, and Pakistan range 3–8% of the populations [7, 10].

Europe(1) β-thalassemia
(2) α-thalassemia
(3) HbCβ 0 or β +  
(4) HbEβ 0 or β +  
(5) SCA
Aside from well-known cases in Italy, Greece, Portugal and Spain, significant prevalence of SCDs and the thalassemias occur in others. In UK more than 200 babies are born annually with SCD. The highest prevalence of 1 in 2,415 is in France due to immigration from more endemic zones [10].

New SCDs/1000 in select areas:
 Nigeria: ≥19
 Ghana: 10–18.9
 S. Arabia: 5–9.9
 Europe: 0.1
Types of SCD seen:
(1) -thalassemia
(2) -thalassemia
(3) HbCβ 0 or β +  
(4) HbEβ 0 or β +  
(5) SCA
New SCDs/1,000 in selected areas [7, 12, 25, 26]:
 Mexico: 0.1–0.19
 Central America: 1–18.9
 South America: 0.1-4.0
 Southeast Asia: 0.2–18.9
 Oceania: 0.1

α-Thalassemia results froms decreased production of α-globin leading to an excess of β-globin in affected adults or an excess of γ-globin in affected newborns. The excess β-globin form unstable tetramers called Hemoglobin H (or HbH) consisting of 4 β-globin chains that exhibit abnormal oxygen dissociation curves. β-Thalassemias are either of the β 0 type (thalassemia major) or of the β + type (thalassemia intermedia). In the β 0 type-thalassemias there is no production of β-globin; hence it is the severer form of β-thalassemia. In the β + type thalassemia some β-globin is produced, making it in the milder form. In either case, however, there is a relative excess of α chains, but these do not form tetramers; instead, they bind to RBC membranes, producing membrane damage, and at high concentrations they form toxic aggregates that lead to anemia. As indicated in the table thalassemias can coexist with SCDs.