Noninvasive prenatal diagnosis of β‐thalassemia by relative haplotype dosage without analyzing proband

BACKGROUND: β‐thalassemia is one of the most common monogenic diseases in the world. Southeast China is a highly infected area affected by four β‐thalassemia mutation types (HBB:c.‐78A>G, HBB:c.52A>T, HBB:c.126_129delCTTT, and HBB:c.316‐197C>T). Relative haplotype dosage (RHDO), a haplotype‐based approach, has shown promise as an application for noninvasive prenatal diagnosis (NIPD); however, additional family members (such as the proband) are required for haplotype construction. The abovementioned circumstances make RHDO‐based NIPD cost prohibitive; additionally, the genetic information of the proband is not always available. Thus, it is necessary to find a practical method to solve these problems. METHODS: Targeted sequencing was applied to sequence parental genomic DNA and cell‐free fetal DNA (cffDNA). Parental haplotypes were constructed with the SHAPEIT software based on the 1000 Genomes Project (1000G) Phase 3 v5 Southern Han Chinese (CHS) haplotype dataset. Single‐nucleotide polymorphisms (SNPs) in the target region were called and classified, and the fetal mutation inheritance status was deduced using the RHDO method. RESULTS: Construction of the parental haplotypes and detection of the inherited parental mutations were successfully achieved in five families, despite a suspected recombination event. The status of the affected fetuses is consistent with the results of traditional reverse dot blot (RDB) diagnosis. CONCLUSION: This research introduced SHAPEIT into the classical RHDO workflow and proved that it is applicable to construct parental haplotypes without information from other family members.