Screening α-Thalassemia In Children Aged Below 7 Years Old In Guangxi Province

ObjectiveTo investigate the incidence and genotypes ofα-thalassemia (α-thal) in children aged below 7 years old in Guangxi Province.MethodsTotal of 2044 children aged below 7 years old were studied, who were selected by multi-stage cluster sampling from the 9 kindergardens in Nanning, Liuzhou and Baise areas. Venous blood was anticoagulated by ACD and analyzed by routine blood test, hemoglobin (Hb) electrophoresis and the high performance liquid chromatography. Theα-globin genes were detected by polymerase chain reaction (PCR) in 267 children with both Mean Corpuscular Volume (MCV)≤70 fl and hemoglobin A2 (HbA2) <3.5% or with the presence of Hb H bands or Hb CS bands in Hb analysis.Results1. Of 267 cases with screening-positive forα-thal among 2044 children aged below 7 years old, 172 cases were diagnosed to beα-thal by PCR. The detection rate ofα-thal was 64.42% in children with screening-positive.2. Among 172α-thal cases, 8 cases were Hb H disease, double heterozygotes of the Southeast Asian type of deletionα-thal-1 (--SEA) combined with 3.7 deletionα-thal-2 (-α^3.7), 4.2 deletionα-thal-2 (-α^4.2), or the Hb Constant Spring (Hb CS,α^CSα), including 3 cases with --SEA/-α^3.7, 2 cases with --SEA/-α^4.2 and 3 cases with --SEA/α^CSα. 118 cases wereα-thal trait, including 114 heterozygotes of the Southeast Asian type of deletionα-thal-1, 2 heterozygotes of the Thailand type of deletionα-thal-1, 1 homozygote of the 3.7 deletionα-thal-2, 1 double heterozygotes of the 3.7 deletion and 4.2 deletionα-thal-2. 46 wereα-thal silent carrier state, including 22 heterozygotes of the 3.7 deletionα-thal-2, 12 heterozygotes of the 4.2 deletionα-thal-2, 11 heterozygotes of the Hb CS, and 1 heterozygote of the Hb Quong Sze (Hb QS,α^QSα).3. The distributions ofα-thal genotypes were as follows: --SEA/αα66.28%, -α3.7/αα12.80%, -α^4.2/αα6.98%,α^CSα/αα6.40%, --SEA/-α3.7 1.74%, --SEA/α^CSα1.74%, --SEA/-α^4.2 1.16%, --Thai/αα1.16%, -α3.7/-α3.7 0.58%, -α3.7/-α^4.2 0.58%, andα^QSα/αα0.58%, respectively.4. The detection rates ofα-thal among 267 children with screening-positive were 57.29% and 69.12% in Han and Zhuang children, 64.97% and 63.64% in boys and girls, 72.92%, 59.43% and 65.49% in Nanning, Liuzhou and Baise, respectively. There were not statistical difference between ethnic groups, gender groups, and city groups as mentioned above, with the statistical probability 0.064, 0.823, 0.257 by chi square test, respectively.5. The distributions of the common genotypes (including --SEA/αα, -α3.7/αα, -α^4.2/ααandα^CSα/αα) and the uncommon genotypes ( including --SEA/-α3.7, --SEA/α^CSα, --SEA/-α^4.2, --Thai/αα, -α3.7/-α3.7, -α3.7/-α^4.2 andα^QSα/αα) ofα-thal in Nanning, Liuzhou and Baise were 91.43%, 100%, 86.49%, and, 8.57%, 0%, 13.51%, respectively. The uncommon genotypes in Baise accounted for the greatest distribution, and the differences between the genotype distributions of the three cities were statistically significant (P=0.003) by Fisher's exact propability test. After the distributions in each of the three cities were compared each other, the differences between Nanning and Baise were statistically significant while the differences between Nanning and Liuzhou, and between Naning and Baise were not.Conclusions1. Of 267 cases with screening-positive forα-thal among 2044 children aged below 7 years old, 172 cases were diagnosed to beα-thal by PCR. The detection rate ofα-thal was 64.42% in children with screening-positive.2. The common genotypes in our study in Guangxi were --SEA/αα, -α^3.7/αα, -α^4.2/ααandα^CSα/ααetc, while the uncommon genotypes were --SEA/-α^3.7, --SEA/α^CSα, --SEA/-α^4.2, --Thai/αα, -α^3.7/-α^3.7, -α^3.7/-α^4.2,α^QSα/ααetc.3. The uncommon genotypes in Baise accounted for greater distribution than in Liuzhou, suggesting that the genotypes ofα-thal in Baise were more complex.4. In China the Thailand type of deletionα-thal-1 (--Thai/αα) ?was first reported to be detected in children.5. It was reasonable for the screening ofα-thal in children aged below 7 years old depending on both MCV≤70 fl and HbA₂<3.5%,besides hemoglobin electrophoresis test.