Deletion, null and mod Phenotypes in the Rh System

Rare phenotypes have been identified that do not react when tested with anti-C, anti-E, anti-c, or anti-e. These individuals lack the genetic material or the functionality of it has been changed or silenced. This is referred to as a deletion phenotype. Many examples of deletion phenotypes have an unusually strong D antigen expression, frequently referred to as exalted D or elevated D. The deletion phenotype is indicated by the use of a dash (-) as in the examples that follow: DC- (DC dash) or Dc- (Dc dash), in which there is deletion of the E gene, or D-- (D dash dash), in which there is deletion of both C and E genes. The antibody potentially made by D--/D-- individuals is called anti-Rh17 or anti-H_o .

A variation within the deletion D-- is recognized and referred to as D .. (D dot dot). The D antigen in D.. is stronger than that in DC- or Dc- samples, but weaker than that of D-- samples. A low prevalence antigen called Evans (Rh:37) accompanies the Rh structure of D.. cells.

Another rare individual may lack all Rh antigen expression and is said to be Rh_null . Their phenotype is written ---/---. These individuals are said to have Rh_null syndrome and demonstrate a mild compensated hemolytic anemia, reticulocytosis, stomatocytosis, slightly to moderately low hemoglobin/hematocrit, increased hemoglobin F, decreased serum haptoglobin, and may have an elevated bilirubin level. The clinical condition of these patients is highly variable. When they require transfusion, Rh_null blood must be given.

Weakened expression of all Rh antigens has also been reported as a rare occurrence and those individuals are said to have the Rh_mod phenotype. When describing this phenotype in written format, parentheses are used as in (D), (C), and (e) to indicate the weakened expression of the given antigen.