Hemoglobinopathies are a group of inherited autosomal recessive hemoglobin disorders, resulting in the homozygous state, in chronic severe anemias. Thalassemias and sickle cell diseases constitute the most monogenic hemoglobin disorders worldwide. Initially described in the tropical and subtropical regions, they are now common all around the world because of migration.
A global epidemiological database for hemoglobin disorders has been established and published recently by the World Health Organization (WHO). Data collected in 229 countries, clearly indicated that hemoglobinopathies constitute a significant health problem in 71% of those countries which include 89% of all births worldwide [1].
The prevalence of carriers of abnormal hemoglobin is within the range of 5-7% in the world and the number of new cases of affected infants is estimated at 300 000 per year. Among them 60 000, are born with beta-thalassemia major annually, the remaining (83%) with Sickle Cell Disease (SCD).

Hemoglobinopathies in Africa:
More than 70% of total hemoglobin disorders are localized in Africa. African population represents less than 10% of the world population but has the highest crude birth rate (39.0‰) as shown in table 1[1] and also the highest rate of affected conceptions (10.78‰) compared to the one registered in the world (2.73‰).

Among these affected conceptions, sickle cell diseases (SCD) are largely prevalent (10.68‰) by comparison to thalassemia syndromes (0.07‰). In addition, it is also in Africa where we registered the highest percentage of under-5 mortality among affected births. Table 2[1] shows some practical service indicators highlighting the needs of care and prevention for hemoglobin (Hb) disorders in African sub-regions. Although only 17.8% from the total births are born in Africa, more than 70% of the annual hemoglobin disorders are also born in Africa. Most of them concerned SCD (85%) and beta-thalassemia major (3.5%). In fact the last percentage corresponds to more than 1500 beta-thalassemia patients born annually; this constitutes a heavy burden with regards to the high cost of treatment of thalassemia and the low income in the majority of African countries.

The most concerned regions by beta-thalassemia in Africa are the western Africa and the Northern Africa with respectively 63.88% and 22.17% of the total annual affected conceptions. The major forms of alpha thalassemia are almost absent in Africa.

In North Africa:
North Africa consists of 5 countries: Mauritania, Morocco, Algeria, Tunisia and Libya (Figure 1) with a total population of 87 millions of inhabitants and a birth rate ranging between 16.8‰ and 40.9‰. The geographical position of this area at the parting of the ways between sub-Saharan African countries and the Mediterranean makes North Africa well concerned by hemoglobinopathies. The inherited hemoglobin disorders are frequently encountered in this population and present a great diversity in the phenotypic expression and genetic aspects.

Many factors may explain, at least partly, this diversity. The most significant factors include the historical context: North Africa witnessed several successive waves of invaders coming from different origins who settled in the region for more or less long periods leading to a large variety of genetic disorders .Ancient social customs, like the high consanguinity rate and endogamy, characterize those populations since centuries, and constitute an additional factor for dissemination of hemoglobinopathies in this area.

Follow-up conditions. Therapeutic approach in hemoglobin disorders, in particular beta-thalassemia, is based on blood transfusion, iron chelation and specific medical care. Patients present almost the same preoccupations related to growth, schooling, professional integration, social support and financial cares.
Because of the high cost of treatment, difficulties in follow-up affect considerably patients in North Africa due to low-income of concerned population. For these reasons, prevention of hemoglobinopathies becomes a necessity and should be a priority of basic health services to reduce its incidence in each country.

Requirements for prevention. The prevention program must take into account the epidemiological and molecular data of each concerned country to set up the adequate strategy that includes usually: Sensitization and information about the disease, Population screening and genetic counselling for carriers, and prenatal diagnosis for couples with affected children

Hemoglobinopathies in Tunisia:
We report here our experience in Tunisia, as an example of a developing country well situated in North Africa. Tunisia occupies the most northerly point of the African continent and covers about 167.000 square km, projecting northward into the Mediterranean Sea, toward Sicily only 86 miles away. It lies approximately midway between the straits of Gibraltar and the Suez Canal. This strategic position in North Africa, makes Tunisia serving a cross road between Europe and Africa and between the Eastern and Western parts of the Arab world.
Berbers were the earliest known inhabitants of the area and racially Tunisia’s population is in the majority, descendants of the union of the Berbers and a large variety of people as Greek, Roman, Vandal, Byzantines, Arab, Spanish, and Turkish who have come to Tunisia since the Phoenicians, first settled in the country 3 000 years ago. Before it got its independence in 1956, Tunisia was a French protectorate throughout 75 years.
As a result of this mixture of races and civilizations, there is no doubt that each of these peoples brought a genetic flow, and had a great influence on the genetic structure of the Tunisians, leading to a high frequency of genetic blood disorders, especially the hemoglobinopathies which represent the most common recessive inherited disorder in Mediterranean population.A recent census gave demographic data of Tunisia as follows [2]: Total population = 9932.4 (x10³); Annual natality rate = 16.8 ‰ ; Estimated births per year = 166834.32; Consanguineous marriages = 33%

Epidemiological data and distribution of main hemoglobinopathies. The presence of the hemoglobinoapathies in Tunisia has been reported as early as 1950 [3]. Since then, several surveys were established to determine the frequency of these affections in the country.
The first results we reported on that field were conducted on Tunisian school children, pregnant women and cord blood samples, noting that beta-thalassemia is the most frequently encountered hemoglobin-pathies among Tunisians4. Then through a national screening conducted in the military recruitment centers, findings indicated that the overall frequency of carriers in Tunisia is 4.48% reaching a higher prevalence in the North Western (10.42%) and in the South Western (5.78%) parts of the country. In addition, further investigations allowed to estimate carriers’ prevalence in different regions of the country (Figure 2).

Geographical distribution allowed to identify the most affected areas which are mainly the cities of Tunis, Béja, Jendouba, Le kef, Bizerte, Gafsa, Tozeur, Kasserine, Sousse as well as in the cities of Zaghouan, Nabeul, Sidi Bouzid, Seliana, Kairouan, Sfax and Kebili.
This observation is of a great interest to guide further research and prevention programs. Beta-thalassemia is the predominant hemoglobin abnormality (2.21%) closely followed by the HbS trait (1.89%) (Figure 3).

Finally, the frequency of alpha-thalassemic genes, deduced from the presence of Hb Bart’s in 2628 cord blood samples, has been estimated to 5.48% [4].
The registered patients are actually over 2400 and the number of at risk couples around 2100 families. The majority of patients (89%) are formed by beta-thalassemic patients, sickle cell patients(SS) and HbS/beta-thalassemia patients (Table 3).

The number of SS patients is unexpectedly much higher than beta-thalassemic patients that would be probably related to the greater tolerance of sickle cell anemia in this country and the natural selection of beta-thalassemia major who, more severely affected, die in early age of life.
Furthermore, according to patient origin, geographical distribution demonstrated once again the higher concentration of beta-thalassemia in the North Western as mentioned above with a newly discovered focus region at Kasserine in the central west of Tunisia where we observed the highest number of beta-thalassemic patients: 27.36% of the total number registered through the country (Table 4).We also note that the most at risk region for sickle cell is the North Western Tunisia (59.70%).

Molecular basis of beta-thalassemia. Identification of beta-thalassemia mutations is also a pre-requisite for prevention programs before undertaking the prenatal diagnosis offered to at risk couples.The spectrum of beta- thalassemia mutations in the Tunisian population (Table 5) revealed a great molecular heterogeneity with actually 28 different beta thalassemia alleles [6]; two common alleles, the codon 39 (CT) non sens mutation and the beta+ IVS1-110 (AG) mutation accounted for 70% of total beta-thalassemia mutations detected in Tunisia; this undoubtedly facilitates the choice of the adapted strategy in the practice of prenatal diagnosis.

Prevention program. Epidemiological and molecular data mentioned above are fundamental to approach prevention program. They allow in particular to identify the most at risk regions and the particular spectrum of beta-thalassemia mutations among Tunisians and also the correlations between phenotype and genotype which may have an important influence in the orientation of genetic counselling.

Prenatal diagnosis. The first setting up of prenatal diagnosis started in 1991 after a transfer of technology based on PCR methods. The System was fully functional at the beginning of 1994. Demands of Prenatal diagnosis (PND) followed a relatively good evolution indicating a progressive increase in the number of at risk couples who desire PND. (Figure 4) Between 1997 and 2006 a total of 268 PND were performed revealing 79 affected fetus (29.5%). Termination pregnancy was accepted in 96.5% of cases; refusal was only in 3 cases (3.8%): for religious reason (1 case), delayed diagnosis (2 cases). According to our experience, acceptability of PND depends on genetic information including the pertinence of genetic counselling and the comprehension by families. In addition, usually at risk couples decide more easily for abortion option when fetus is affected by beta-thalassemia major because of the severity of the disease compared to SS fetus or another SCD. This is also true when existence of an affected proband in the family.
Despite a large information and sensitization campaign on hemoglobinopathies, many pregnant women from at risk families do not present or present too late, (after the third trimester of gestation) for prenatal test, thus they lose the prenatal diagnosis benefit.

Neonatal screening. Neonatal screening started in Tunisia as a pilot study in two maternities in the city of Tunis and aimed at detecting sickle cell disease and beta0 thalassemia at early age in order to reduce the under-5 mortality rate in the affected infants. Our experience was successful (Table 6) allowing to take in charge precocely the affected babies and to identify numerous at risk couples to be counseled during their eventual next pregnancies; this pilot program has been extended recently to a high risk region in the North Western Tunisia.

Premarital screening. Premarital screening was carried out randomly on 53 couples; 18% were detected at risk suggesting the importance of this test to secure at risk couples against affected progenitor. The screening program needs to be supported by public awareness and regular education in concerned populations.

Discussion:
Hemoglobinopathies constitute a real public Health problem in the large majority of African countries and contribute, at least partly, in the increasing rate of infant mortality and morbidity. In the only North Africa Region, demographic and epidemiologic data allow to estimate the number of new cases of babies who are born with a severe form of hemoglobinoathie at as much as 419 every year in Tunisia, Algeria and Morocco and around 2000/year if we include Mauritania and Libya where carrier rates of abnormal hemoglobin are much higher (Table 7)[5,7,8,9,10,11].

We can easily imagine the heavy burden of this large number of patients on health care resources, knowing that the direct cost of the management for one patient is estimated to about 7000DT/year (5000 US $).
In reality the whole problem still lies in the difficulties in the diagnosis of abnormal hemoglobin traits and in the very limited economic resources that do not permit to take in charge correctly the numerous patients already identified. Several affected children die before reaching the 10^th year of life. Still this figure is probably understated because of the existence of local concentration of the disease and of the high degree of consanguinity, reaching a rate of 70% in some rural areas. In addition, heterozygote detection should be conducted carefully in these countries where iron deficiency is a major problem for the diagnosis of heterozygous beta-thalassemia since it may mask an elevation of HbA₂ level. Our experience in Tunisia demonstrates that premarital screening is the best option and should be mandatory in any prevention program for hemoglobinopathies. Thus most at risk couples are identified early for prenatal diagnosis in the first pregnancy and would regularly produce healthy offspring. Unfortunately many at risk couples yet discover  their risk only after the birth of their first affected child. In Tunisia, neonatal screening was decided to reach the maximum of concerned families; its efficiency is more evident in population of at risk regions. Success will depend on a good coordination and a good cooperation between parents and medical staff.
Moreover, in the most African countries, data on epidemiology of hemoglobinopathies are scarce, and insufficiently precise to undertake a solid program of control and prevention for these genetic diseases. The few preventive actions conducted in this context remain uncompleted and need to be developed efficiently by opting to the best adapted way, economical and cost-effective.
To improve the situation, public education about thalassemia and sickle cell diseases is of a great importance and should be carried out through periodic meetings addressed to health professionals including doctors and nurses working in the community, and family members. Also, all means of mass media are helpful as well as the sensitization through patient parents’associations that facilitates the contact with families and the diffusion of information through didactic supports (brochures, booklets ect).