RHD (gene)

RHD (gene) is a gene located on chromosome 1 in humans that encodes the Rh blood group D antigen, commonly known as the Rh factor. The presence or absence of this antigen on the surface of red blood cells determines whether a person's blood type is Rh positive (Rh+) or Rh negative (Rh-). This distinction plays a critical role in blood transfusion and pregnancy, as incompatibilities between the Rh status of a mother and her fetus can lead to Hemolytic Disease of the Newborn (HDN).

Structure and Function

The RHD gene is part of the Rh blood group system, which includes several antigens, with the D antigen being the most significant due to its immunogenicity. The gene spans approximately 75 kilobases on chromosome 1p34.1-1p36 and consists of 10 exons. The protein product of the RHD gene is a transmembrane glycoprotein that is expressed on the surface of red blood cells. It plays a role in the structural integrity of the red blood cell membrane and possibly in ion transport.

Genetic Variability and Rh Variants

Variations in the RHD gene can lead to the expression of different Rh phenotypes. The most common variation is the complete deletion of the RHD gene, resulting in the Rh negative phenotype. Other variations can lead to weak or partial D antigens, known as Rh Variants, which can complicate Rh typing and transfusion compatibility.

Clinical Significance

The clinical significance of the RHD gene lies primarily in its role in blood transfusion and pregnancy. Individuals who are Rh negative do not naturally have antibodies against the D antigen, but they can develop them if exposed to Rh positive blood through transfusion or pregnancy. This immune response can lead to hemolytic reactions in transfusions or HDN in subsequent pregnancies if the fetus is Rh positive.

In pregnancy, Rh incompatibility between an Rh negative mother and an Rh positive fetus can lead to the mother's immune system attacking the fetal red blood cells, leading to HDN. This condition can cause severe anemia, jaundice, and even fetal death. The administration of Rho(D) Immune Globulin to Rh negative mothers during and after pregnancy has significantly reduced the incidence of HDN.

Genetic Testing

Genetic testing for the RHD gene can determine an individual's Rh status and identify Rh variants. This information is valuable for ensuring compatibility in blood transfusions and managing Rh incompatibility in pregnancy.

See Also

• Blood type
• Rh blood group system
• Hemolytic Disease of the Newborn (HDN)
• Rho(D) Immune Globulin