Distribution of Hemoglobinopathies and Thalassemias in Qatari Nationals Seen at Hamad Hospital in Qatar

Fawzi Z.O., Al Hilali A., Fakhroo N., Al Bin Ali A. and Al Mansour S.
Department of Laboratory Medicine and Pathology
Hamad Medical Corporation, Doha, Qatar

Abstract:

Several reports indicate that haemoglobinopathies and thalassemias are the most common genetic abnormalities in the population of the Arabian- Peninsula. However the exact frequencies of these abnormalities among the Qatari population has not yet been determined. We surveyed the results of all hemoglobin-electrophoresis performed in Hematology laboratory at Hamad Hospital over a period of 78 months (Jan.1994- June.2000) together with the results of all other relevant tests to highlight the distribution of these disorders among the Qatari patients seen at Hamad Hospital.

The size of the group analyzed was 3275 of whom 1702 were Qatari and 1573 were non-Qatari residents of different nationalities. The survey of Qatari results revealed that 30.43% of all Qatari patients tested carry ß-thalassemia (minor, intermedia or major), 12.28% carry µ-thalassemia (minor or intermedia) while 0.53% were labeled as having Hereditary Persistence of Fetal Hemoglobin (HPFH). ß-thalassemia is the most common type of thalassemic disorders seen in the Qatari patients, accounting for 71.25% of all thalassemias encountered in this group.

Out of Qatari patients tested 16.33% were found to carry a structurally abnormal hemoglobin variant of one type or another. Sickle cell hemoglobin is the most common structural hemoglobin variant detected where it is found in 14.63% of those tested and constituting about 83.97% of all structural hemoglobin variants detected. Hb.D was found in 1.41% of those tested and constituted 12.42% of all structural hemoglobin variants detected in this group. Other structurally abnormal hemoglobin variants such as Hb. E and Hb.C were less common. As expected, almost all possible combinations between different types of structural hemoglobin variants and different types of thalassemias could be identified.

Considering the fact that the hematology laboratory at Hamad Hospital is the only laboratory in the State of Qatar that performs hemoglobin- electrophoresis we hope that this study will reflect for the first time a reasonable idea about the prevalence of thalassemia and other types of hemoglobinopathies among the indigenous Qatari population and help to provide a comprehensive baseline information for any proper future epidemiological studies to establish the exact frequencies of these genetic disorders among Qatari nationals and for any future molecular-based studies for elucidation of the molecular basis of these disorders in this population.
Key Words: Hemoglobinopathies and Thalassemia ,
Qatari Population.

Introduction:

Hemoglobinopathies and thalassemias are two distinct groups of inherited disorders of hemoglobin synthesis arising from mutations and/or deletions of one or more of the globin genes resulting in production of structurally abnormal hemoglobin variants in the former and reduced rate of synthesis of structurally normal globin chains in the latter. Although the carrier states of both conditions may be clinically silent, the homozygote or the doubly heterozygote states may manifest clinically as anemia of varying degree of severity.

The frequency of these disorders varies considerably with geographic locations and racial groups. Thalassemias and sickle cell hemoglobin in particular are endemic in geographic areas where malaria is endemic or had been endemic in the past and these are included in the thalassemia belt that spread from Spain through the Mediterranean Basin, Africa, the Middle East, India, Tropical Asia and the Pasific.The positive evolutionary selection for these genetic mutations is thought to be related to the resistance against malaria infection provided by the heterozygous state of those disorders specially of sickle cell hemoglobin.

At the molecular level these disorders are extremely heterogeneous and this is best exemplified by the fact that more than 180 mutations have so far been described world wide for Beta- thalassemia alone. Genetic studies of DNA linked to ßs-gene suggests that this gene had probably arisen from three different mutations in tropical Africa (1). A different pattern of polymorphism associated with the ßs-gene in Saudi- Arabia and India suggests that the Asian gene may have arisen from an independent mutation (1).

Many single gene disorders had been reported in the population of the Arabian Peninsula including different types of structural hemoglobinopathies, thalassemias, enzymopathies such as Glucose-6- Phosphate- Dehydrogenase (G6PD) deficiency, phenyleketoneuria, cystic fibrosis, hemophilia, fragile X- syndrome, spinal muscular atrophies and many others (2). However according to the reports of the Third and Fourth Annual Meetings of the WHO Working Group for the Community Control of Hereditary Anaemias 1985; (HMG/WG/85.8, WHO Geneva, Switzerland), hemoglobinopathies and thalassemias are the most frequently encountered single gene disorders among the Arab population with a frequency of up to 9.9/1000 births in Saudi Arabia (2). Several mutant alleles responsible for the production of these disorders have been identified in the populations of the Arabian Peninsula with varying frequencies and this is most probably related to continuous human migration and admixture.

The high incidence of consanguity among the populations of the Arabian Peninsula plays a very important role in maintaining the recessive pattern of inheritance and increases the risk of homozygous or doubly heterozygous clinically affected offsprings creating great psychological and financial stresses on the families and great burdens on the financial resources of many countries in the region.

Many reports on the frequencies of these disorders in the different countries in the Arab world have been published. Also extensive researches have been conducted and more are under way in an attempt to draw genetic mapping of these disorders in the different communities in the region. However very little data is currently available about the prevalence of these disorders among the Arab population in the State of Qatar.

Despite the fact that this is a hospital based study including only those cases referred to the laboratory for investigation we hope that this study will for the first time provide an insight about the frequency of these disorders among the nationals of the State of Qatar. This is because Hamad Hospital laboratory is the only laboratory that performs hemoglobin-electrophoresis in the country and the patients investigated include all those seen primarily in the hospital and those being referred from all other state or private health centers and laboratories in addition to the good number of patients included in the study, 3275 including 1702 Qatari nationals, compared with the overall population of around 550,000 including indigenous Qatari nationals of around 200,000.

Materials & Methods:

Results of all hemoglobin electrophoresis and related tests such as full blood counts, sickling test, screening for Hb. H inclusion bodies and quantitation of Hb - A2 and Hb - F performed by hematology laboratory at Hamad Hospital over a period of 78 month (January 1994- June 2000) were analyzed to look at the pattern of distribution of thalassemias and the different types of hemoglobinopathies amongst Qatari nationals and non-Qatari residents in the state. The results of 3275 patients including 1702 Qatari nationals (797 males and 905 females) and 1573 non-Qatari patients of different nationalities (839 males and 734 females) were analyzed.

The majority of patients were investigated for thalassemia or hemoglobinopathies according to the request of their physicians as part of their evaluation for an unexplained hypochromic microcytic anaemia with normal iron balance or for microcytosis in the absence of significant anaemia. Some patients were investigated as part of a family study when a member was found to have an evidence of thalassemia or a structural hemoglobin variant. In some other instances the investigations were initiated by the laboratory when the peripheral blood counts and red cell indices or the morphology of the red cells were suggestive of one of these disorders.

Patients with features suggestive of iron deficiency anaemia or in whom the iron status was not evaluated were deferred from hemoglobin electrophoresis until their iron status had been evaluated and their iron deficiency had been corrected.

The data analyzed include results of full blood counts, sickling test, screening for Hb. H inclusion bodies, hemoglobin electrophoresis and Hb- A2 and Hb- F quantitation. Full blood counts were performed using Coulter hematology analyzers for the first five and half years evaluated and Cell-Dyne- 4000 analyzers were used during the last twelve months. Sickling test was performed in all samples using the slide method and sodium- metabisulphite as a reducing agent. Hemoglobin electrophoresis on cellulose acetate strips at alkaline pH together with quantitation of Hb-A2 using micro-column chromatography and Hb-F quantitation by alkaline denaturation were performed on all samples. When hemoglobin electrophoresis on cellulose acetate revealed a band in Hb-S region or a thick band in Hb-A2 region then hemoglobin-electrophoresis was repeated on citrate agar at an acid pH in order to separate Hb-S from other abnormal hemoglobins with similar electrophoretic mobility on cellulose acetate, such as Hb-G and Hb-D and to separate Hb-C from other hemoglobin variants that migrate to the same region, such as Hb-E and Hb-O Arab.

Results:

he results of all 3275 patients tested were analyzed and the summary of results is shown in Table 1.
In 16% of the patients hemoglobin electrophoresis showed a normal pattern while in 8.2% the results were considered to be inconclusive. The latter group included patients in whom iron deficiency anaemia could not be definitely excluded and

Table 1: Summary of all results 

 patients in whom the results of hemoglobin electrophoresis were considered to be affected by recent blood transfusion.

Out of all patients tested 32.98% were considered to have ß-thalassemia minor, 0.61% to have ß-thalassemia intermedia and 1.37% were found to have ß-thalassemia major. About 7.36% were labeled as µ-thalassemia trait and 0.89% as µ-thalassemia intermedia (Hb-H / Hb-Barts disease). About 0.52% of patients were empirically labeled as Hereditary Persistence of Fetal Hemoglobin (HPFH) based on the observation of high Hb-F level in presence of microcytosis in the absence of anemia.

Of all patients tested a total of 11.36% were carrying the sickle hemoglobin. About 5.8% were found to have sickle cell trait (A/S) while a total of 3.29% were found to have sickle cell disease (S/S, S/ß⁰, S/C) with 2.05% being homozygous for Hb-S (S/S). Of those 1.44% had sickle cell anemia with a high Hb.F level while the remaining 0.61% had normal Hb.F levels. Out of all patients about 1.19% were considered to be doubly heterozygous for Hb -S and ß0- thalassemia (S/ ß⁰- thal) and 2.17% were considered to have sickle cell trait plus µ- thalassemia based on the observation of microcytosis and Hb- S levels of about 30% or less. In many cases the distinction between sickle cell anemia (S/S) and S/ß⁰ thalassemia was made empirically, based mainly on the observation of marked microcytosis in addition to the features of sickle cell disease in the latter group while in some cases the diagnosis was based on a family study. Hemoglobin -D trait was found in 1.22% of patients and Hb- D disease (D/D, D/ ß⁰- thal.) in 0.46%. Other structural hemoglobin variants such as Hb-C and Hb- E were rarely observed as shown in Table 1.

In 18.47% of the patients hemoglobin electrophoresis showed a normal pattern but in the presence of microcytosis with normal or very slightly reduced hemoglobin level the possibility of µ-thalassemia trait or ß- thalassemia trait with normal Hb-A2 level could not be completely excluded.

Table (1) also shows a summary of the results of Qatari patients when analyzed separately. Of all Qatari patients investigated 16.86% showed a completely normal hemoglobin electrophoresis pattern and in 8.58% the result of hemoglobin electrophoresis was considered inconclusive for the same reasons as mentioned above. In 19.74% of patients the results of hemoglobin electrophoresis showed a normal pattern, however in the presence of microcytosis with normal or slightly reduced hemoglobin level it was not possible to rule out completely the possibility of µ-thalassemia or normal Hb- A2 ß-thalassemia.

ß-thalassemia trait was detected in 28.02%, ß-thalassemia intermedia in 0.11% and ß-thalassemia major in 0.76%. About 8.05% of patients were labeled as µ- thalassemia trait and 0.99% were labeled as µ-thalassemia intermedia (Hb-H/Hb-Bart’s).

Of all Qatari patients tested 14.63% were carrying the sickle hemoglobin. Sickle cell trait (A/S) was found in 7.46%, S/µ- thalassemia in 3.23% and sickle cell disease (S/S, S/ß⁰) was diagnosed in 3.94% of patients with 2.40% considered to be homozygous for the sickle cell hemoglobin (S/S). Of this group, 1.70% had sickle cell anemia with high Hb- F levels while the remaining 0.70% had sickle cell anemia with normal Hb- F.

The distinction between homozygous Hb- S (S/S) and S/ ß⁰ double heterozygous state was empirically made as described above.

A small group of patients were found to have Hb-D with 1.12% having Hb- D-trait & 0.3% having Hb-D disease (D/D, D/ ß⁰). Both Hb-C and Hb- E were rarely encountered, seen only in 0.05% & 0.23% respectively (Table 1).

About 0.53% of Qatari patients tested were empirically labeled as Hereditary Persistence of Fetal Hemoglobin (HPFH) based on criteria outlined above.

As expected all examples of combinations between thalassemias and structural hemoglobin variants were observed.

Hb-S / ß thalassemia was seen in 1.53% and Hb-S /µ– thalassemia in 3.23% of patients tested and few patients with Hb- D/ ß-thalassemia were also encountered.

Results of non- Qatari patients are also summarized in Table (1).Of those eleven patients, one required azathioprine and four required methotrexate to control the symptoms.

Discussion:

Analysis of the available data showed that both thalassemias and sickle cell hemoglobin are common between both Qatari and non-Qatari patients included in this study. Table (1) summarizes the results of both Qatari and non-Qatari residents. It can be seen that 30.43% of Qatari nationals and 42.34% of non-Qatari studied were found to have ß-thalassemia (Trait, intermedia or major) while µ- thalassemia (trait and intermedia) was seen in 12.28% of Qatari nationals and 8.38% of non-Qatari residents.

ß-thalassemia is more common than µ-thalassemia in both groups accounting for 71.25% of all thalassemias seen in Qatari and 83.56% of all thalassemias seen in non-Qatari, while µ-thalassemia accounted for 28.75% and 16.54% of all thalassemias in Qatari nationals and non-Qatari residents respectively (Table 1).

Among the hemoglobinopathies, sickle cell hemoglobin is the most common abnormal hemoglobin variant in both groups, seen in 14.63% of Qatari and 7.82% of non-Qatari, constituting about 89.57% of all structural hemoglobinopathies detected in the former group (Fig 1) and 73.65% of all structural hemoglobinopathies detected in the latter. Hb.D though far less common ranks second to Hb.S where it is seen in 1.41% of all Qatari tested and 1.96% in non-Qatari, constituting 8.63% of all structural hemoglobin variants seen in the former group and 18.56% in the latter. Hb.E and Hb.C are less common in both groups; Hb.E however is more frequently seen in non-Qatari than in Qataris (Table 1).



Figure 1: Distribution of Hemoglobinopathies in Qataris

In 19.7% of Qatari and 17.1% of non-Qatari tested, hemoglobin electrophoresis showed a normal pattern but the possibility of µ- thalassemia trait or ß- thalassemia trait with normal Hb-A2 could not be completely excluded since this group of patients showed microcytosis in the absence of iron deficiency anemia as documented by the absence of anemia and normal iron profiles. This group of patients although empirically labeled as possible µ-thalassemia needs further clarification at a molecular level to verify this assumption and to rule out the possibility of normal Hb-A₂ ß- thalassemia trait.

The pattern of distribution of both thalassemias and hemoglobinopathies among Qatari nationals as suggested by this study seems to be quite similar to that of the different Arabian Gulf populations and other Arab populations in the middle east. Several studies have shown that thalassemias and structural hemoglobinopathies are the most frequent single gene disorders among the various populations of the Arabian Peninsula ⁽³⁾. It was reported that among these populations the most frequently encountered structural hemoglobinopathy is the sickle cell hemoglobin with a reported frequency of up to 17% in some parts of Saudi Arabia ⁽³⁾ (Table 2). In Bahrain the frequency of sickle cell hemoglobin among neonates is reported to be 11%-18% ⁽⁴⁾. In Egypt sickle cell hemoglobin is very rare along the River Nile but different frequencies have been reported in the Western desert near the Libyan borders ranging from 0.38% in the coastal areas to 22.17% in Siwa Oasis ^(5,3) (Table 2). Among the Libyan Arabs in the south of the country the prevalence of sickle cell trait and sickle cell anemia is 4.4% and 1.2% respectively while the prevalence of sickle cell anemia in the eastern part of the country is only 0.005%^(6,3). Available data show a frequency for sickle cell hemoglobin of 6.0% in Tunisia, 5.3%-6.0% in Oman, 2.4% in U.A.E., 5.25% in Iraq, 1.52%-10% in Sudan, 0.83%-3.5% in Algeria, 0.34% in Lebanon and a frequency of less than one percent in Syria ⁽³⁾ (Table 2).

Both ß-thalassemia and µ-thalassemia are prevalent in the majority of the Arab populations screened with varying frequencies. In the eastern part of Libya the frequency of ß-thalassemia is reported as 11.2% compared with a frequency of 3.2% in the southern parts of the country ^(6,3). In Saudi Arabia the reported frequency of ß-thalassemia ranges from 1% in some areas to 5% in others ^(7,3). Among the Jordanians the prevalence reported is 3.3% ⁽⁸⁾ while in Yemenis and Emiratis frequencies of less than one percent have been reported ⁽⁸⁾.

Alpha-thalassemia of both deletional and non-deletional types has been reported to be very frequent among the Arab population. As reported 24.2% of Bahraini neonates were shown to have a µ- thalassemia trait ⁽⁴⁾. In Saudi Arabia the frequency of µ-thalassemia ranges from 12%-60% in different parts of the country with the highest frequency in the eastern province ^(6,7) while an incidence of 45% has been reported for the Omanis ^(2,6).

In 70% of Qatari with sickle cell anemia (S/S) the level of Hb- F is considerably elevated. It will be interesting to elucidate at a molecular level whether this is actually a result of an interaction with coexisting thalassemia or whether it is related to particular types of ß^s-gene mutations which are prevalent in this population.

There remains a group of patients comprising 18.47 % of the whole group tested and 19.74 of Qatari with significantly low MCV in the absence of anemia or iron deficiency and a completely normal hemoglobin electrophoresis pattern. In those patients it was impossible to rule out the possibility of µ-thalassemia or ß-thalassemia with a normal Hb.A2. Careful study at a molecular level is also needed to elucidate the underlying genetic abnormality in this group of patients and their families.


Conclusion:

As in other populations of the Arabian Peninsula hemoglobinopathies and thalassemias are very common among Qatari nationals. ß-thalassemia is more common than µ-thalassemia and sickle cell hemoglobin appears to be the most common structural hemoglobin variant. Since both thalassemias and sickle cell hemoglobin are common in this population it was not surprising to see all types of combinations between these disorders and it would be interesting to look at the effects of theses various combinations on the clinical expression of these disorders. In particular it would be interesting to look at the effect of co- inheritance of µ-thalassemia and HPFH on the clinical expression of sickle cell disease.

About 70% of Qatari patients with sickle cell disease have high levels of Hb- F and it would be of interest to find whether this is related to coinheritance of ß-thalassemia, HPFH or whether that is related to the type of the ß^s - gene mutation which is prevalent in this population.

Molecular analysis is needed to draw a genetic mapping of the different mutations underlying these disorders in the Qatari



     Figure 2: Distribution of Thalassemias in Qataris

Table 2: Reported Prevalence of Sickle Cell Hemoglobin In Some of The Arab Populations

 population and it would be of particular interest to elucidate the underlying genetic defects, if there are any, in that group of patients with significantly low MCV, normal hemoglobin level and normal hemoglobin electrophoresis pattern and the underlying genetic mutations in those patients with high level of Hb- F which were empirically labeled as having hereditary persistence of fetal hemoglobin (HPFH).

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