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

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.

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.

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.

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.