Frequencies of HKααand anti-HKααAlleles in Chinese Carriers of Silent Deletionalα-Thalassemia

The HKαα (HongKongαα) allele is an unusual rearrangement of the α-globin gene cluster containing both the −α3.7 (rightward) and αααanti 4.2 crossover deletion/duplication. The anti-HKαα (anti-HongKongαα) allele is the reciprocal product containing both the −α4.2 (leftward) and αααanti 3.7 unequal crossover deletion/duplication. In clinical practice of thalassemia screening, gap-polymerase chain reaction (gap-PCR) approaches are used to detect the common −α3.7 and −α4.2 deletions of α-thalassemia (α-thal). Because the HKαα and anti-HKαα alleles also contain the single α-globin gene deletion, individuals with these alleles would be misdiagnosed as −α3.7 or −α4.2 carriers. This would likely produce misleading or incorrect information in genetic counseling. In this study, we investigated the HKαα and anti-HKαα alleles in Chinese carriers of silent deletional α-thal, and reported their frequencies to be 2.27 and 0.35% in −α3.7 and −α4.2 carriers, respectively. Given the rarity of the HKαα and anti-HKαα alleles, a routine screening for these two rearrangements are unlikely to be necessary on most occasions.