A novel 4.9 Kb deletion at beta-globin gene is identified by the third-generation sequencing: Case report from Baoan, China

Thalassemia is a common inherited haemoglobin disorder worldwide, several methods have been utilized in the step-wise screening. Even though hundreds of mutations in globin genes have been reported, novel mutations are continuously emerging as the development of DNA sequencing.The case is a 27-year-old female with abnormal values of routine hematological indices, who was admitted for genetic screening of thalassemia. Genomic DNA was extracted and used for genetic assays cover 26 mutations in HBA and HBB genes: gap-PCR and agarose gel electrophoresis were performed to detect deletions, while PCR-reverse dot blot was used to detect point mutations. The next- and third- generation sequencing were used to identify the known and potential novel genotypes of thalassemia, and multiplex ligation-dependent probe amplification (MLPA) was used for genotype validation.Hematological results indicate microcytic hypochromic anemia, high HbA2 (7.2%) and high HbF (6.2%). None of the known genotypes of thalassemia were matched for this case, but a novel 4.9 Kb deletion at HBB gene (hg38, Chr11: 5226187-5231089) was discovered by the third-generation sequencing, the novel deletion was also validated by MLPA (8 probes, 11p15.4: 203314-207652).This study suggests the third-generation sequencing has promising potentiality to discover novel genotypes (especially deletions) of thalassemia.