Prevalence of Thalassemia among Newborns: A Re-visited after 20 Years of a Prevention and Control Program in Northeast Thailand
1 Centre for
Research and Development of Medical Diagnostic Laboratories, Faculty of
Associated Medical Sciences, Khon Kaen University, Khon Kaen, Thailand.
2 Regional Health Promotion Center 7, Khon Kaen, Thailand.
Received: April 27, 2018
Accepted: July 28, 2018
Mediterr J Hematol Infect Dis 2018, 10(1): e2018054 DOI 10.4084/MJHID.2018.054
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To provide accurate prevalence information of thalassemia in northeast
Thailand, authors performed thalassemia screening in newborns after 20
years implementation of a prevention and control program.
Materials and Methods
Hb analysis and DNA analysis. Hb fractions and quantifications were performed using automated capillary electrophoresis (CE) (Capillarys 2 Flex Piercing: Sebia, Lisses, France), applying the manufacturer protocol. Genomic DNA was prepared from leukocytes using the standard method. Identification of the α0-thalassemia (--SEA and --THAI) and α+-thalassemia (3.7 and 4.2 kb deletions) were routinely performed in our laboratory using gap-PCR. Hb Constant Spring and Hb Paksé were identified using multiplex allele-specific PCR.[2,7,11,12,13] Screening for α-globin gene triplication (αααanti3.7) was done using a PCR method as previously described. Common β-thalassemia genes found in Thailand were examined using allele-specific PCR assays.
|Table 1. Thalassemia genotypes found in 350 newborns.|
|Table 2. Number of allele, gene frequency and incidence of each thalassemia gene observed among 350 newborns.|
Twelve Hb patterns and corresponding genotypes of the newborns are shown in Table 3. A normal Hb FA pattern was identified in 183 cases including 145 normal babies, 33 α+-thalassemia carriers (-α/αα), four carriers of non-deletion α+-thalassemia (αTα/αα) and a baby with β-thalassemia heterozygote (αα/αα, β17/βA). Hb Bart’s was detected in most of the babies with α-thalassemia, i.e., 46 of 48 cases, and in 2 cases of homozygous Hb E. The results showed that the amount of Hb Bart’s was increased with the increasing numbers of the defective α-globin genes. Newborns with single α-globin gene defect [(α+-thalassemia; -α3.7 or -α4.2) or Hb Constant Spring and Hb Paksé] have Hb Bart’s at 0.4 ± 0.1% and 0.7 ± 0.1%, respectively. The Hb Bart’s levels found in individuals with two α-globin gene defects were 2.6 ± 1.2%, 1.6 ± 0.7% and 6.2 ± 2.1% for heterozygous α0-thalassemia (--/αα), homozygotes α+-thalassemia (-α/-α) and compound heterozygous α+-thalassemia/Hb Constant Spring (-α/αTα), respectively. Newborns with Hb H disease (--/-α) (n=2) had Hb Bart’s at 21.9% and 18.6%, respectively. These results indicated that while Hb Bart’s detected by CE could be a good marker for α-thalassemia in newborns, it is not sensitive enough since some cases of α+-thalassemia carriers had no detectable Hb Bart’s. In contrast, CE is very sensitive in identifying cases with Hb E in newborns. It could demonstrate Hb E peak in all 116 cases of Hb E carriers, and variable levels of Hb E could be measured in all newborns with βE-mutation.
|Table 3. Hemoglobin types and fractions found among 350 newborns in corresponding to genotypes. Values are presented as mean ± SD or as raw data where appropriate.|
Another approach to monitoring the performance of a prevention and control program is to look prospectively at newborns. In this study, we have addressed this in northeast Thailand after 20 years of a prevention and control program. Examination for all thalassemic genes found in Thailand was carried out on 350 cord blood specimens collected consecutively and prospectively at delivery. As shown in Table 1, we have noted as many as 22 thalassemia genotypes among 184 of 350 (52.6%) newborns. Moreover, no case with the three severe thalassemia diseases targeted in a prevention and control program was encountered. As shown in Table 2, high incidence for all forms of α-thalassemia (35.8%) and Hb E (39.1%) are detected. In contrast, the frequency of β-thalassemia is relatively much lower (0.6%). This pattern of thalassemia and hemoglobinopathies found in newborns is very similar to those documented in adult population observed in a micro-mapping survey in the region as well as in other areas of Thailand as shown in Table 2. Here is indicated effective prevention of new case with severe thalassemia but the corresponding thalassemic genes are still prevalent in the region. In fact, this is not unexpected since by theory allele frequency in the population remains constant from generation to generation.
Taking the data on Hb analysis into diagnostic consideration for the three important thalassemia carriers, we found that Hb Bart’s detected by capillary electrophoresis is a very good marker for reporting α-thalassemia in newborns. Different levels of Hb Bart’s were detected for different α-thalassemia genotypes and the higher level, the more α-globin gene defect (Table 3). However, as also observed in other studies, Hb Bart’s may be undetectable in some cases of α-thalassemia especially those with one α-globin gene defect (-α/αα or αTα/αα).[19,20] In contrast, we found that all cases with Hb E, either in heterozygote or homozygote had detectable levels of Hb E on the capillary electrophoresis system. This simple examination should permit making initial recognition of the cases before definite diagnosis by DNA analysis. A problem remains for β-thalassemia. In two cases of β0-thalassemia carriers encountered (αα/αα, β17/βA), we observed the same Hb FA pattern with that of the normal newborns i.e. Hb F (92.9 & 86.8 % v.s. 84.2 + 4.5 %) and Hb A (7.1 & 13.0 % v.s. 15.8 + 4.5 %). This confirms that diagnosis of β-thalassemia is relatively difficult in newborns unless DNA analysis is performed.[16,17,20,21]
Nonetheless, our study demonstrates the current prevalence of thalassemia and hemoglobinopathies among newborns in northeast Thailand after a prevention and control program of thalassemia has been launched for more than 20 years. Since the three important thalassemia carriers including α0-thalassemia, β-thalassemia, and Hb E are still prevalence in the population, an effective prevention and control program of thalassemia should be continuously operated in the region.
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