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?
r (dce) — the person is D-negative, C-negative, and E-negative
R1 (DCe) — the same haplotype that dominates European ancestry
R0 (Dce) — D-positive, C-negative, E-negative, with c and e in cis
R2 (DcE) — D-positive with E, the haplotype that defines Rh-null
Why can anti-G be mistaken for anti-C plus anti-D on a routine panel?
G is serine 103, present on C+ cells and on most D+ cells, so the serum reacts with both C+ D− and C− D+ panel cells
G is proline 226, the E/e residue, so every E+ cell looks D-positive
G is made only when RHD is deleted, so G-positive cells are always D-negative
G is a Lewis-adsorbed glycolipid, so every secretor panel cell types C+ and D+
A patient types D− C− c− E− e−. The red cells are stomatocytes and survival is shortened. Which statement is correct?
This is ordinary rr; stomatocytes are expected whenever RHD is deleted
This is Bombay (hh); missing H always silences Rh antigens
This is K0; Kell-null cells lose Rh proteins because both systems sit on chromosome 1
This is Rh-null from either an RHAG regulator mutation or an RH-locus amorph, and immunized patients may make anti-Rh29
Sections you finish are checked off in the contents.