A case report recently published in Transfusion and Apheresis Science describes a patient diagnosed with a rare variant of the RhD antigen. Such variants can impact blood transfusion compatibility, a critical consideration in preventing adverse outcomes in diseases such as hemolytic disease of the fetus and newborn (HDFN).
“This report marks the first case in China of anti-D alloimmunizationAlloimmunization When a person’s immune system develops antibodies against foreign antigens from the same species—such as when an Rh-negative mother’s body forms antibodies against her baby’s Rh-positive red blood cells. in patients with the D variant,” the authors wrote.
There are three major versions of the RhD antigen. Patients with the normal D type have the full-length version of the RhD antigen and are considered Rh-positiveRh-Positive A blood type trait that means your red blood cells have the Rh(D) antigen.. Those with the DEL type have a deletion in the RhD gene and are considered Rh-negativeRh-Negative A blood type trait that means your red blood cells lack the Rh(D) antigen..
The D variant, which was the focus of this study, refers to altered expressed of the RhD antigen. This variant is further subdivided into weak D, in which there are a reduced number of D antigensAntibody A protein made by the immune system that recognizes and attacks foreign substances, such as bacteria, or in HDFN, fetal red blood cells carrying incompatible antigens. on red blood cells, and partial D, in which the structure of the antigen is altered. While some patients with the D variant are considered Rh-positive, others are not, highlighting the need to accurately classify RhD blood type in patients requiring blood transfusions.
Read more about HDFN testing and diagnosis
The case report described a 63-year old woman presenting with acoustic neuroma, a benign tumor found in the ear. Pre-operative bloodwork revealed the presence of anti-D alloantibodies, and subsequent serological testing showed that the patient had a variant D antigen.
The authors then evaluated the patient’s RHD gene through a polymerase chain reaction assay, discovering that exons 5-9 were not present. Genetic sequencing showed that while exons 1, 2, 3, 4 and 10 were normal, exons 5-9 appeared to be replaced with sequences from the RCHE gene. Thus, the individual was classified as having the RHD-CE(5-9)-D genotype, which corresponds with the rare DBT2 phenotype.
“Both serological and molecular detection of the D variant are essential to ensure the safety of blood transfusions,” the study concluded.
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