HBA2 Gene Conversion Disrupts Reverse Dot-Blot Hybridization Genotyping: A Prenatal Case of Non-Deletional...

This study reports a misdiagnosed case of non-deletional α-thalassemia caused by HBA2 gene conversion, whose inheritance pattern does not conform to the classical Mendelian inheritance model. Gap-polymerase chain reaction (Gap-PCR) combined with PCR-reverse dot-blot (PCR-RDB) revealed that the fetus was homozygous for HbQS, while the father was heterozygous for HbQS, and the mother was homozygous for HbCS and concurrently heterozygous for the β-globin CD41-42 mutation. Sanger sequencing confirmed that the fetus was heterozygous for the HbQS, while the mother was heterozygous for the HbCS. In addition, we identified two variants of the HBA2 gene in both the mother and fetus: IVS II-55 T > G and IVS II-119 (-G) (+CTCGGCCC). These variants suggest a gene conversion event between HBA2 and HBA1, which likely contributed to the misdiagnosis of RDB as homozygous. The multiplex ligation-dependent probe amplification (MLPA) results further substantiated the occurrence of gene conversion. Ultimately, we confirmed that the corrected α-thalassemia genotypes for the fetus and the mother are α^QSα/α^{[IVS II-55 T>G, IVS II-119 (-G) (+CTCGGCCC)]}α and α^CSα/α^{[IVS II-55 T>G, IVS II-119 (-G) (+CTCGGCCC)]}α, respectively. This study elucidated a molecular mechanism of gene conversion that complicates the diagnosis of α-globin gene clusters, providing critical evidence for clinical genetic counseling and prenatal diagnosis.