The pedigree analysis and prenatal diagnosis of Hong Kongαα Thalassemia and the sequence analysis of Hong Kongαα Allele

Background Thalassemia is one of the most common monogenic hemolytic disorders in the world. Hong Kong alpha alpha (HK alpha alpha) thalassemia was initially found among the people of southern China. Because of the complexity of genetic changes in HK alpha alpha thalassemia, we lack a precise sequence analysis of the HK alpha alpha allele. Here we aim to detect the specific genotype and trace the law of inheritance of this rare genotype. Methods We recruited an unprecedented huge pedigree containing 11 individuals carrying the HK alpha alpha thalassemia gene and 4 nongenetic-related patients suffering from HK alpha alpha from south China. Regular hematological analysis and routine genetic screening were performed on the pedigree and two-round nested PCR (polymerase chain reaction) for HK alpha alpha thalassemia were performed on each individual. The first-generation gene sequencing was performed on six individuals, including four nongenetic-related patients. Result We found that five family members were positive for the HK alpha alpha allele. Patients II-2, III-1, and II-3 with only HK alpha alpha/--(SEA) or HK alpha alpha/-alpha(4.2) presented with alpha-thalassemia minor trait. ROMAN NUMERAL ONE-1, the carrier of both HK alpha alpha/-alpha(3.7) and beta(41-42)/beta(N), showed a typical beta-thalassemia trait. Fetus with genotype HK alpha alpha/-alpha(4.2) alone was not likely to suffer from any deleterious effects after birth. The whole sequence of HK alpha alpha allele revealed that HK alpha alpha alleles in the six patients shared a high similarity, implying that all HK alpha alpha alleles are likely from the same ancestor. Moreover, pedigree and sequencing analyses demonstrated that the HK alpha alpha allele contained alpha alpha alpha(anti4.2) mutation, -alpha(3.7) mutation, and a fragment from alpha-hemoglobin gene; thus, the composition and formation of HK alpha alpha allele was revealed. Finally, the high similarity and composition of HK alpha alpha alleles implies that once HK alpha alpha formed, alpha alpha alpha(anti4.2) and -alpha(3.7) mutations tended to be a fusion gene and quite impossible to be inherited separately. Conclusion The two-round nested PCR is an effective method to detect HK alpha alpha allele. Besides, our study for the first time revealed the sequence of the HK alpha alpha allele, the evidence of the same ancestor with HK alpha alpha thalassemia and enriched the composition as well as the formation mechanism of HK alpha alpha allele, and immediately opened up novel potential diagnosis and prenatal counseling for HK alpha alpha thalassemia.