7.1 Rh Genetics and Antigens
Key Takeaways
- RHD and RHCE sit on chromosome 1p36.11 in opposite (tail-to-tail) orientation; homology drives RHD-CE-D hybrids. European D-neg is usually a deleted RHD; African D-neg is often the RHDψ 37-bp-insertion pseudogene.
- The five everyday antigens are D, C, c, E, and e. G is serine 103 on C+ or most D+ proteins, so anti-G serologically mimics anti-C+D until adsorption separates the specificities.
- Wiener R1 is Fisher-Race DCe, R0 is Dce, and r is dce. The letter d is a placeholder for a missing RHD — it is not an antigen and has no antithetical antibody.
- R1 (DCe) is the most common haplotype in people of European ancestry, R0 (Dce) is the most common in people of African ancestry, and r (dce) is the most common Rh-negative haplotype in every population.
- Compound antigens (f/ce, Ce, cE, CE) exist only when both antigens are cis. RhAG on chromosome 6 is required for Rh expression; regulator or amorph Rh-null produces stomatocytes and shortened red-cell survival.
7.1 Rh Genetics and Antigens
Quick Answer: RHD and RHCE sit on chromosome 1p36.11 in opposite (tail-to-tail) orientation. The five everyday antigens are D, C, c, E, and e. G is serine 103 and rides on C+ or most D+ cells, so anti-G looks like anti-C+D. Translate Wiener, Fisher-Race, and Rosenfield without blinking. R1 (DCe) is the most common haplotype in people of European ancestry; R0 (Dce) is the most common in people of African ancestry; r (dce) is the most common Rh-negative haplotype. Compound antigens (Ce, ce/f, cE, CE) exist only when the two antigens are cis. RhAG (chromosome 6) parks Rh proteins in the membrane. Rh-null (regulator or amorph) makes stomatocytes and shortens red-cell survival.
The June 9, 2026 BB outline parks the entire Rh system at II.B.3. ABO is terminal sugars. Rh is two homologous proteins, a partner glycoprotein, and a set of haplotypes you must speak in three dialects. If you cannot convert R1r into DCe/dce and then into which compound antigens are present, later antibody-ID items will eat you.
Two genes, opposite orientation, one haplotype
RHD and RHCE live at 1p36.11. Each gene has 10 exons and they are about 97% identical. They are transcribed in opposite orientation (tail-to-tail), with a small intervening gene (TMEM50A / SMP1) between them. That geometry plus the homology is why gene conversion and hybrid genes (RHD-CE-D, RHCE-D-CE) keep appearing in African-ancestry patients and in partial D. You inherit the pair as a haplotype. Crossing-over between RHD and RHCE is uncommon in a single generation, so D, C/c, and E/e travel together as a block.
- RHD present and intact → D antigen (RH1).
- RHD deleted — the common European D-negative mechanism, unequal recombination between flanking Rhesus boxes — → no D.
- RHDψ (RHDpsi) — a 37-bp insertion in exon 4 plus a nonsense mutation, common in African D-negative people — is an inactive RHD. Serology is D-negative. A naive RHD PCR that does not detect the psi will falsely call the person D-positive.
- RHCE encodes the C/c and E/e polymorphisms on one protein. C versus c is several linked SNPs; the teaching residue is Ser103 (C) versus Pro103 (c). E versus e is Pro226 (E) versus Ala226 (e).
Rh proteins are nonglycosylated, 12-pass membrane proteins. They do not carry the sugars ABO does. They need RhAG to reach the surface. Chapter 5 already used RHD and RHCE as the chromosome-1 example; this section is the antigen map those genes produce.
The five antigens plus G
| ISBT / Rosenfield | Common name | Gene product | Teaching residue or rule |
|---|---|---|---|
| RH1 | D | RhD | Presence or absence of a functional RHD |
| RH2 | C | RhCE | Ser103 on RhCE |
| RH3 | E | RhCE | Pro226 on RhCE |
| RH4 | c | RhCE | Pro103 on RhCE |
| RH5 | e | RhCE | Ala226 on RhCE |
| RH12 | G | RhD or RhCE | Serine 103 on a D or C protein |
G antigen is not a sixth everyday typing reagent on the rack, but it is an everyday exam trap. Serine 103 creates G whether that serine sits on RhD or on a C-bearing RhCE. Therefore:
- C+ cells are G+, including r' = dCe, which is D-negative.
- Most D+ cells are G+ even when they are C-negative, including R0 = Dce.
- rr (dce) cells are D-negative, C-negative, and G-negative.
Anti-G reacts with C+ or D+ panel cells and looks exactly like anti-C+D. It is not anti-C plus anti-D until you prove the specificities. Section 7.3 works the adsorption. The genetics point here is G = Ser103, so r' cells and R0 cells both carry G and neither carries the other person's missing major antigen. Rare D variants lack G; do not invent them on a standard panel item.
Three nomenclatures, one haplotype
BB still asks you to translate. Fisher-Race writes the antigens in DCE order and uses d to mean RHD absent — d is a placeholder, not a gene product. Wiener writes the haplotype as a single symbol. Rosenfield writes what reacted: RH:1,2,-3,-4,5.
| Wiener | Fisher-Race | Antigens | Rosenfield shorthand |
|---|---|---|---|
| R1 | DCe | D, C, e | RH:1,2,-3,-4,5 |
| R2 | DcE | D, c, E | RH:1,-2,3,4,-5 |
| R0 | Dce | D, c, e | RH:1,-2,-3,4,5 |
| Rz | DCE | D, C, E | RH:1,2,3,-4,-5 |
| r | dce | c, e | RH:-1,-2,-3,4,5 |
| r' | dCe | C, e | RH:-1,2,-3,-4,5 |
| r'' | dcE | c, E | RH:-1,-2,3,4,-5 |
| ry | dCE | C, E | RH:-1,2,3,-4,-5 |
Wiener decoding: R = D present, r = D absent. 1 or ' = C, 2 or '' = E, 0 = ce (no C, no E), z or y = CE. R1 is DCe, not “Rh-positive type 1” as a clinical blood type. A phenotype is two haplotypes. R1r is DCe/dce and types D+ C+ c+ E− e+. R1R1 is DCe/DCe and types D+ C+ c− E− e+. R0r is Dce/dce and types D+ C− c+ E− e+. Write the two haplotypes before you predict f or Ce.
Haplotype frequencies you will be handed as distractors
| Haplotype | European ancestry | African ancestry | East Asian ancestry | Exam headline |
|---|---|---|---|---|
| R1 (DCe) | ~42% | ~17% | ~70% | Most common Caucasian (and Asian) haplotype |
| R0 (Dce) | ~4% | ~44% | ~3% | Most common African American haplotype |
| r (dce) | ~37% | ~26% | ~2% | Most common Rh-negative haplotype in every group |
| R2 (DcE) | ~14% | ~11% | ~21% | Second most common D+ haplotype in Europeans after R1 |
| r' (dCe) | ~1% | ~2% | rare | The C+ D− haplotype that carries G |
| r'' (dcE) | ~1% | rare | rare | The E+ D− haplotype |
| Rz, ry | rare | rare | rare | Do not invent them as common |
Rh-negative phenotype frequency tracks r: about 15% of people of European ancestry, about 5–8% of people of African ancestry, and about 0.1–0.5% of East Asian ancestry. The most common Rh-negative haplotype is r (dce) even in populations where Rh-negative people are scarce. Do not call R0 “the African Rh-negative haplotype.” R0 is D-positive.
Phenotype consequences: the common Caucasian D+ types are R1r and R1R1. The common African American D+ types are R0r and R0R0 (D+ C− E−). If a stem says “most likely genotype in an African American D+ C− E− patient,” answer R0R0 or R0r, not R2r. Asian D-negativity is rare because r is rare; a serologic D-neg East Asian donor is the person you later worry is Del (Section 7.2).
Compound antigens are cis geometry
A compound antigen exists only when two RhCE antigens are encoded on the same haplotype.
- f (ce, RH6): c and e cis. Present on r (dce) and R0 (Dce).
- Ce (RH7): C and e cis — the R1 and r' antigen.
- cE (RH27): c and E cis — R2 and r''.
- CE (RH22): C and E cis — the rare Rz and ry.
R1R2 (DCe/DcE) types D+ C+ c+ E+ e+. That person has Ce (from R1) and cE (from R2) but is f-negative because c and e are trans, not cis. R1r (DCe/dce) is f-positive because r supplies cis-ce. Predicting f from a phenotype without haplotypes is how you fail a panel-cell selection item.
C in trans to RHD (Ceppellini) can weaken D — an r' facing R0 or R2. That is haplotype geometry from Chapter 5. Do not call Ceppellini weakening partial D.
RhAG and the Rh-null phenotypes
Rh-associated glycoprotein (RhAG), gene RHAG on chromosome 6, is the chaperone and a core protein of the Rh complex. RhD and RhCE do not traffic normally without it. RhAG is also a gas/ammonium transporter. It is its own ISBT system (RHAG, 030), not an Rh antigen you type with anti-D.
Rh-null means no D, C, c, E, or e (and no G, f, or Ce). Two genetic routes reach the same empty membrane:
- Regulator type: RHAG mutations. RHD and RHCE may be intact, but the proteins never sit in the membrane. This is the more common Rh-null.
- Amorph type: inactivating mutations at the RH locus — typically deleted RHD plus silenced RHCE. RHAG is normal. No Rh protein is made.
Both produce the same membrane penalty. The Rh complex helps organize the cytoskeleton. Rh-null red cells are stomatocytes, have increased osmotic fragility, and have shortened survival. The clinical picture is a chronic, usually compensated hemolytic anemia (Rh-deficiency syndrome). LW antigens are missing or depressed because LW needs Rh protein as a partner; S/s/U and Fy5 can look weak. Do not call Rh-null a Duffy-null, and do not call the cells spherocytes.
An immunized Rh-null patient can make anti-Rh29 (total Rh) or anti-Rh17 (Hr0, the high-prevalence antigen on every cell that has any RhCE protein). Almost every donor unit is incompatible. You need other Rh-null units or autologous blood. Rh-mod is a leaky RHAG defect with weak residual Rh antigens and a milder hemolysis.
Exam traps
- Treating d as a real antigen. d means RHD is absent.
- Calling R0 Rh-negative. R0 is Dce — D-positive.
- Saying the most common African American haplotype is r or R1. It is R0.
- Treating anti-G as proven anti-C+D without adsorption.
- Predicting f on every C+c+e+ cell. R1R2 is f-negative.
- Confusing regulator (RHAG) with amorph (RH locus).
- Calling Rh-null spherocytes. They are stomatocytes.
Which Rh haplotype is the most common in people of African ancestry, and what antigens does it encode?
Why can anti-G be mistaken for anti-C plus anti-D on a routine panel?
A patient types D− C− c− E− e−. The red cells are stomatocytes and survival is shortened. Which statement is correct?