Identification of maternal ^Gγ(^Aγδβ)⁰ thalassemia through retrospective reanalysis of prenatal cfDNA sequencing data

Non-invasive prenatal screening (NIPS) is widely used to detect chromosomal abnormalities such as trisomies 21, 13, and 18 and is also effective in screening for copy number variations (CNVs). However, the routine application of NIPS to detect smaller CNVs within the HBB gene, specifically ^Gγ(^Aγδβ)⁰ thalassemia, has yet to be well documented. This study aims to evaluate the efficacy of cfDNA-based maternal carrier screening in routine screening for ^Gγ(^Aγδβ)⁰ thalassemia.

We performed a retrospective analysis of 107,300 pregnant women who underwent NIPS at Longgang Maternal and Child Healthcare Hospital in Shenzhen from December 2017 to May 2022. Using an improved algorithm, we reanalyzed NIPS data to identify maternal ^Gγ(^Aγδβ)⁰ thalassemia. Positive cases were confirmed by multiplex ligation-dependent probe amplification (MLPA) using peripheral blood leukocytes.

Among the 107,300 NIPS analyses, 38 maternal deletion CNVs within the HBB gene were identified using the improved algorithm, with a prevalence of 0.035% (38/107,300). MLPA confirmed that all detected deletions were consistent with ^Gγ(^Aγδβ)⁰ thalassemia. The positive predictive value (PPV) for detecting ^Gγ(^Aγδβ)⁰ thalassemia by cfDNA-based maternal carrier screening was 100%. Among the 38 ^Gγ(^Aγδβ)⁰ cases, 9 were also associated with α-thalassemia deletions, including 4 cases with -^SEA/αα, 4 with -α^3.7/αα, and 1 with -α^4.2/αα. No cases of homozygosity or compound HBB gene variants were observed.

^Gγ(^Aγδβ)⁰ thalassemia is not uncommon in China, and repurposed NIPS methodology for maternal genomic analysis in detecting HBB gene deletions is a reliable method for identifying maternal carriers of this disease.