A novel α Globin Gene Cluster Duplication, αααα380 Heterozygous ß0-Thal Variant, Leading to a Blood Transfusion-Dependent Phenotype.

ABSTRACT

To assess the effectiveness of three-level prevention and control of thalassemia, we routinely collect samples from transfusion-dependent individuals and perform genetic analysis. Here, we report on a 10-year-old boy requiring blood transfusions with routine thalassemia gene test results of αα/αα, and ßCD41/42/ßN, but he had thalassemia-like changes in his appearance and a high need for frequent blood transfusions, suggesting a case of thalassemia major in childhood. Given these equivocal results, samples from the family members were collected for further analysis. A multiplex ligation-dependent probe amplification assay was used to detect a multicopy number variant of the α globin gene cluster in the proband. The variant was detected as a long fragment repeat of 380 Kb using CNV assay technique, which contains the entire α globin gene cluster, describing it as αααα380/αα. Analysis of family members suggested that both the brother and mother of the proband carried the variant, and both MCV and MCH values were reduced in carriers. Individuals carrying multiple copy number variants of the α globin gene cluster exist in the population. Individuals carrying such variants who are also heterozygous for the ß0 thalassemia variant result in an imbalance in the α/ß chain ratio, potentially leading to the creation of individuals with a severe anemia genotype. Most secondary prevention and control laboratories currently do not include variants with increased α gene copy number in their testing, which is one of the blind spots of prevention and control efforts. In order to provide more accurate genetic counseling to test subjects, especially in regions with high rates of thalassemia carriage, testing laboratories should pay attention to individual genotype-phenotype matches to avoid the under-detection of such variants.