Discordant prenatal and postnatal RhD typing caused by a novel RHD frameshift variant (c.540del; p.Leu181CysfsTer48) in Swedish individuals.

Abstract

Background and objectives: Non-invasive prenatal testing (NIPT) for fetal RHD genotyping is widely used to guide anti-D prophylaxis, but discrepancies between predicted fetal RhD status and postnatal serological typing can occur due to variant RHD alleles. This study aimed to confirm and characterize a suspected novel exon 4 deletion in RHD using multiple molecular methods and to assess inheritance.

Materials and methods: NIPT predicted an RhD-positive fetus in an RhD-negative pregnant woman, whereas postnatal serology showed an RhD-negative phenotype. Molecular analysis of RHD was performed using the RBC-Ready Gene CDE kit (Inno-Train, Kronberg, Germany), targeted next-generation sequencing (NGS) and Sanger sequencing in the family and in an unrelated RhD-negative woman.

Results: Targeted NGS identified a single-nucleotide deletion in the RHD gene (c.540del), predicted to result in a frameshift and premature termination (p.Leu181CysfsTer48). Sanger sequencing confirmed the variant in the newborn and demonstrated paternal inheritance, with the father heterozygous for the deletion. The same variant was also identified in an unrelated RhD-negative woman of Swedish origin; notably, the newborn's father was also of Swedish origin.

Conclusion: This case illustrates a limitation of current NIPT approaches, which detect RHD sequences but not gene functionality. Molecular follow-up is crucial in cases of discordant RhD typing.