Very rare (< 50 people in the world). These patients are completely devoid of all Rh-type antigens (49) on the wall of the red blood cells. The Rh group is one of the 36 antigenic systems of the human erythrocytes. It is the 2nd largest group after the ABO group. In the Caucasian population, 85 % of the people are Rh+.

The absence of Rh antigens on erythrocytes leads to Rhnull syndrome. 

Genetically, this peculiarity is due:

-        in 20% of cases (so-called "amorphous" form) to a RH haplotype (RH or RHCE, on 1p36.13-p34.3), silent in double dose. This  haplotype known as RH: - -, does not produce either RHD nor RHCE. The reason is not obvious in that the sequence of the transcribed RhCE, Rh50, and CD47 do not always show anomalies;

-        in 80 % of cases (the so-called "regulator" form) to an inhibitory gene blocking the expression of normal RH haplotypes that are present, and which will be transmitted to patient's children. This inhibitory gene blocks the RHAG protein (for RH-associated glycoprotein) (6p11-p21), which appears essential to the assembly or to the intracellular path of the RH

   protein.

These two types of HRnull are indistinguishable serologically. The RH29 antigen found on all erythrocytes that are not RHnull is not detected.

Clinical picture: a fragility of the erythrocytes, characterized by spherocytis and osmotic fragility leading to chronic hemolytic anemia, often well compensated but sometimes requiring a splenectomy. The clinical picture is actually close to hereditary spherocytosis,or Minkowski-Chauffard's disease (see this term). But the severity of the clinical consequences, varies greatly from one subject to another within the same family.

Anesthetic implications: 

complex transfusion problem because these patients produce antibodies after a single transfusion. It is therefore very difficult to find a compatible donor outside their family. It is necessary, through a self-transfusion protocol, to keep the blood of these people frozen in a national centre, or to use other national blood transfusion centres that may have such frozen blood in stock.

References : 

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Updated: June 2020