Extensive clinical, serologic and molecular studies lead to the first reported Rh_mod phenotype in Argentina

A highly reduced expression of Rh antigens in the erythrocyte membrane is the main feature of Rh_mod , an extremely rare phenotype. Mutations within RHAG gene, which encodes RhAG glycoprotein and modulates Rh antigen expression and Rh complex formation, are the molecular events responsible for the Rh_mod phenotype. Here we report a clinical, serologic, and molecular study of an Argentinean proband with Rh-deficiency syndrome.

Rh antigens, RhAG and CD47 glycoproteins were studied by serologic methods in the proband, her parents and sister. Osmotic fragility and viscoelastic parameters were also examined. RHD zygosity was analyzed by RFLP-PCR. RHD, RHCE, and RHAG genes were studied by Sanger sequencing.

No Rh antigens were detected in the proband by standard techniques. However, adsorption-elution and anti-RhAG tests showed that the proposita was Rh_mod . Reduced expression of CD47, enhanced osmotic fragility, and surface viscosity alterations giving rise to spherocytes were observed in the patient. Sequencing analysis showed that a c.920C>T mutation in RHAG Exon 6 was present in a homozygous state in the proband and in a heterozygous state in the rest of the family. This novel missense mutation caused the p.Ser307Phe amino acid substitution in Transmembrane Segment 10 of the RhAG glycoprotein.

This comprehensive study determined the causes of the proband's anemia allowing the diagnosis of Rh-deficiency syndrome.