LAUSR

Alpha-thalassemia is characterized by a microcytic hypochromic anemia, and the majority of a-thalassemia (80– 90%) is caused by deletion(s) of a-genes in chromosome 16p13.3 [1, 2]. Approximately 50 deletions from the aglobin cluster have been reported (http://globin.bx. psu.edu/cgi-bin/hbvar/counter), and the deletions varied from 2.4 kb to the whole a-globin gene cluster. In southern China, common types of deletional a-globin mutations include the South East Asian deletion (SEA), the rightward deletion (a), and the leftward deletion (a), with the SEA type at the highest frequency of 4.1–8.7% [3]. Although carriers of a-thalassemia are asymptomatic, couples who are both carriers have a 25% chance of conceiving a homozygous fetus each pregnancy, which may clinically manifests as hemoglobin Bart’s hydrops fetalis. Most of the hemoglobin Bart’s hydrops fetalis die in uterus or shortly after birth, often accompanied by congenital abnormalities [4]. Besides, it increases the risk of maternal complications, including preeclampsia, placental dystocia, and mirror syndrome [5]. Therefore, those with thalassemia traits clinically but no mutations detected in routine molecular screening should receive further molecular testing, and prenatal diagnosis are essential if both of the couple carry the same type of thalassemia genes. At present, the most common detection method for deletional thalassemia with known break points is gappolymerase chain reaction (Gap-PCR) [6]. Multiplex Ligation Dependent Probe Amplification (MLPA) was developed to screen for unknown copy-number variations (CNVs) [7], but the distance between MLPA probes generally ranges between 3 and 10 kb that requires the use of long-range PCR and primer walking to sequence the break point completely, which might be rather time consuming and labor-intensive. The custom comparative genomic hybridization (CGH) technology has significant advantages in resolution, reproducibility, and precision in mapping imbalances and is considered as a promising method in characterizing CNVs, including deletions in HBA and HBB loci [8, 9]. Here, we describe a case with a novel 44.6-kb deletion causing a-thalassemia in two members of a Chinese family. The probands, 23-year-old female and 21-year-old male, were siblings, with apparent a-thalassemia traits, demonstrated with decreased mean corpuscular volume (MCV), mean corpuscular Hb (MCH), and HbA2. The hematological parameters were presented as follow: elder sister Hb 122 g/L, MCV 68.9 fL (NR 82–100 fL), MCH 20.6 pg (NR 26–32 pg), HbA2 1.8% (NR 2.75–3.5%); younger brother Hb 147 g/L, MCV 70.4 fL (NR 82– 100 fL), MCH 21.5 pg (NR 26–32 pg), HbA2 2.3% (NR 2.75–3.5%). Common a-thalassemia deletion mutations (–/,-a/and -a/) and nondeletion mutations (aa/, aa/, aa/) were scanned and revealed negative. Iron deficiency was excluded. Both of their parents were of Yunnan ancestry, and in a nonconsanguineous marriage. The results were highly suggestive that the probands may carry a less common defected allele, and they would like to receive further diagnosis. So the probands and their family members were referred to Guangdong Thalassemia Diagnostic Center for further investigation. After pretest counseling, peripheral blood samples were obtained from the probands and their family members for further analyses. Sample collection procedures were approved by Guangdong Women and Children Hospital Institutional Review Board and Ethics Committee of Guangzhou Medical College, China. Written informed consents were obtained from the probands and their family members. Genomic DNA was isolated from peripheral blood by standard procedures using an automation system Lab-Aid 820 (Zeesan Biotech, Xiamen, China). Common a-thalassemia deletion mutations (–/,-a/and -a/) and nondeletion mutations (aa/, aa/, aa/) were scanned and revealed negative using protocols described previously [10]. The specific Gap-PCR detecting less common HBA deletional mutations revealed negative, including –/,–/,–/, –/,–/. DNA sequencing was applied to detect mutations in a-globin genes as previously described, and it suggested there were no mutations on the a-globin