I decided, someone knows more than I do, so if you are so inclined and understand this information, would you please share it in english terms we can understand and I will put the "translation" up on the blog for everyones education. Thanks, maybe this was a good thing to do or maybe it wasn't. I guess we will find out soon enough.
Excerpt: RH negs - Another Example Of Polygenic Inheritance - C, D, or E
http://waynesword.palomar.edu/aniblood.htm
by Waynes Word,
| Rh Factor: Another interesting example of polygenic inheritance is the Rh factor. Unlike the A-B-O blood types where all the alleles occur on one pair of loci on chromosome pair #9, the Rh factor involves three different pairs of alleles located on three different loci on chromosome pair #1. In the following diagram, 3 pairs of Rh alleles (C & c, D & d, E & e) occur at 3 different loci on homologous chromosome pair #1. Possible genotypes will have one C or c, one D or d, and one E or e from each chromosome. For example: CDE/cde; CdE/cDe; cde/cde; CDe/CdE; etc. |
 In order to determine how many different genotypes are possible, you must first determine how many different gametes are possible for each parent, then match all the gametes in a genetic checkerboard (See the following Table 3). Although the three pairs of genes are linked to one homologous pair of chromosomes, there are a total of eight different possible gametes for each parent: CDE, CDe, CdE, Cde, cDE, cDe, cdE, and cde. This number of gametes is based on all the total possible ways these genes can be inherited on each chromosome of homologous pair #1. [It is not based on the random assortment of these genes during meiosis in the parents because all three genes are closely linked together on the same chromosome; therefore, all three genes tend to appear together in the same two gametes: CDE and cde.] The possible different genotypes are shown in the following Table 3: |
Gametes
|
CDE
|
CDe
|
CdE
|
Cde
|
cDE
|
cDe
|
cdE
|
cde
|
CDE
|
CDE/
CDE |
CDE/
CDe |
CDE/
CdE |
CDE/
Cde |
CDE/
cDE |
CDE/
cDe |
CDE/
cdE |
CDE/
cde |
CDe
|
CDe/
CDE |
CDe/
CDe |
CDe/
CdE |
CDe/
Cde |
CDe/
cDE |
CDe/
cDe |
CDe/
cdE |
CDe/
cde |
CdE
|
CdE/
CDE |
CdE/
CDe |
CdE/
CdE |
CdE/
Cde |
CdE/
cDE |
CdE/
cDe |
CdE/
cdE |
CdE/
cde |
Cde
|
Cde/
CDE |
Cde/
CDe |
Cde/
CdE |
Cde/
Cde |
Cde/
cDE |
Cde/
cDe |
Cde/
cdE |
Cde/
cde |
cDE
|
cDE/
CDE |
cDE/
CDe |
cDE/
CdE |
cDE/
Cde |
cDE/
cDE |
cDE/
cDe |
cDE/
cdE |
cDE/
cde |
cDe
|
cDe/
CDE |
cDe/
CDe |
cDe/
CdE |
cDe/
Cde |
cDe/
cDE |
cDe/
cDe |
cDe/
cdE |
cDe/
cde |
cdE
|
cdE/
CDE |
cdE/
CDe |
cdE/
CdE |
cdE/
Cde |
cdE/
cDE |
cdE/
cDe |
cdE/
cdE |
cdE/
cde |
cde
|
cde/
CDE |
cde/
CDe |
cde/
CdE |
cde/
Cde |
cde/
cDE |
cde/
cDe |
cde/
cdE |
cde/
cde |
| Polygenic inheritance in the Rh blood factor. Every genotypic combination with DD or Dd is classified as Rh Positive (red). This is about 85% of the U.S. population because the D gene is more common than the C and E genes. Every genotypic combination with dd is classified as Rh Negative (blue). Since the ratio of C and E genes is much less than D genes, approximately 15% of the U.S. population are Rh negative (dd). | Consolidating the duplicates, a total of 10 genotypes are homozygous recessive for the d allele (dd); however, nine of these genotypes are actually positive for the C and E factors: Cde/cde (0.46%), Cde/Cde (0.0036%), cdE/cde (0.38%), cdE/cdE (0.0025%), Cde/cdE (0.006%), CdE/cde (0.008%), CdE/Cde (0.0001%), CdE/cdE (0.0001%), and CdE/CdE (0.00001%). | Therefore, only about 0.86% of the U.S. population are positive for C and E. Expressed as a decimal, this is 0.0086 or 8.6 out of 1000. This is why Rh incompatibility involving the C and E genes is rare in the U.S. population. |
Antigen
|
Immune Antibodies (In Blood Plasma)
|
||
(RBC Membrane)
|
anti-C
|
anti--D
|
anti-E
|
C (RhC)
|
------
|
------
|
------
|
D (RhD)
|
------
|
RhoGAM & Biology TypingSerum
|
------
|
E (RhE)
|
------
|
------
|
------
|
Rh antibodies primarily utilized in immunoglobulin serums.
|
| More than 98% of all cases of hemolytic disease of the newborn (maternal-fetal blood incompatibility) are caused by the D antigen, also referred to as RhD and Rh Positive (+). This is why RhoGam and standard blood typing kits for general biology labs only contain anti-RhD (anti-D) antibodies. Anti-C and anti-E antibodies against the C and E antigens can be associated with maternal-fetal blood incompatibility, but this is uncommon and only occurs in a small percentage of non-RhD cases. Apparently immune globulins (such as RhoGam) are not available to prevent these rare cases. According to Dr. Kenneth J. Moise, Jr., Director of the Division of Maternal-Fetal Medicine at University of North Carolina Medical School at Chapel Hill, more than 43 other RBC antigens have been implicated in the non RhD cases. Especially problematic are the Kell (K1), c, Duffy (Fya) and Kidd (Jka and Jkb) antigens. | A recent study from a tertiary referral
center in New York found 550 cases of antibodies associated with
hemolytic disease of the newborn in 37,506 blood samples taken from
women of reproductive age (1.1% incidence). Anti-D occurred in 25% of
the samples, anti-Kell in 28%, anti-c in 7%, anti-Duffy in 7%, anti-Kidd
in 2%, anti-E in 18%, anti-C in 6%, anti-MNS in 6%, and anti-Lutheran
in 2%. The following link contains a summary of Rh maternal-fetal blood
incompatibility from the UNC Department of Obstetrics and Gynecology:
|
perinatology.com
http://www.perinatology.com/Archive/Isoimmunization.htm
The numerous antigens on the surface of red blood cells have been placed into groups. Many people are familiar with the Rhesus (Rh) group as it is the most clinically relevant. However the non-Rh groups such as Kell, MNS, and Kidd have assumed increasing importance as the incidence of Rh-D sensitization has decreased. Nonetheless sensitization to Rh antigens (non-D ) is still responsible for the largest proportion of hemolytic disease in the newborn (HMD)[1].
According to the Fisher and Race theory of inheritance [2] :
- The Rh alleles (D,Cc, Ee) are inherited as a complex of three loci .One set from each parent.
- A person is Rh-positive if they possess the D allele and Rh negative if it is absent.
- The hypothetical "d" allele has not been identified.
Source: The Rhesus Site There are more than forty antigens in the Rh system including weak D (formerly called Du variant). Mothers typed as weak D appear to be Rh negative on blood screening.
- The majority of mothers with weak D are Rh (D) positive. However, the presence of the C allele causes the D antigen to be weakly expressed [3].
- Mothers or infants typed as weak D are usually treated as Rh positive.
- The true genetic Du variant is an incomplete form of D antigen and may rarely become D immunized.
- The rare occurrence of a D immunized true genetic Du mother may be sufficient reason to treat a weak D mother with RhIg when the nature of the Du variant is in doubt[4].
Incidence of the Rh Negative Blood Group in Various Populations[5]
| Chinese and Japanese | |
| North American Indian and Inuit | |
| Indo-Eurasian | |
| African American | |
| Caucasian | |
| Basque |
Pathogenesis
Blood production in the fetus begins at about 3 weeks' and Rh antigen has been identifed in the red cell membrane bas early as 38 days after conception. [6]- The initial response to D antigen is slow sometimes taking as long as 6 months to develop.
- Re-exposure to the antigen produces a rapid immunological response usually measured in days.
- The sensitized mother produces IgG anti-D (antibody) that crosses the placenta and coats D-positive fetal red cells which are then destroyed in the fetal spleen.
- Mild to moderate hemolysis (red cell destruction) manifests as increased indirect bilirubin (red cell pigment).
- Severe hemolysis leads to red blood cell production by the spleen and liver.
- Subsequently, hepatic circulatory obstruction (portal hypertension) with placental edema interferes with placental perfusion and ascites develops.[5]
- Hepatomegaly, increased placental thickness, and polyhydramnios often precede the development of hydrops (fetal heart failure).[5]
- As liver damage progresses decreased albumin production results in the development of anasarca, and effusions.
- Overall, 16% of Rh-negative women will become sensitized after their first pregnancy if not given Rhogam.
- ABO incompatibility reduces this risk to 4-5%.[5]
The reduced risk of Rh sensitization with ABO incompatibility may result from the rapid clearance of incompatible red cells thus reducing the overall exposure to D antigen.
Screening
Initial blood type and screening for antibodies is part of routine prenatal care. The evaluation of a positive antibody screen should include identification of the antibody and its titer. Identification of antibody [1,5,7 ]- There are several classes of antibodies. The two of interest are IgM and IgG. If the antibody can be identifed as an IgM then it does not cross the placenta and there is no risk of hemolysis to the fetus.
- "Naturally occurring" IgM antibodies may result from antigenic stimulus such as bacteria, which have antigens on their surfaces chemically similar to blood group antigens. Anti-M antibodies are usually IgM , but IgG Anti-M does occur and is capable of causing hemolytic disease.
- Anti-K, anti-D, anti-E, anti-Fya , anti-Jka, and antibodies directed against Rh antigens comprise the majority of antibodies resposible for hemolytic disease of the newborn .
- The following antibodies ARE NOT associated with Hemolytic disease of the newborn (HMD):
- Lewis:Lea, Leb
- Lutheran:Lua , Lub
- I
- Duffy: Fyb
- P
- Jkb
| Vw, Mur, Hil, Hut, Batty, Becker, Berrens, Evans, Gonzales, Hunt, Jobbins, Rm, Ven, Wrightb ,Ytb, , Ge, Jra, Coa-b,Xga |
- The following antibodies ARE associated with HMD:
| Dia, Dib ,PP1Pk, Far, Good, Lan,LW, Mta, U ,Wr a, Zd |
Titer
- A titer of > 1:4 is considered sensitized.
- The method used should be stated as the titer will vary according to the method.
- An albumin titer of 1:16 is equal to an indirect antiglobulin test (IAT) titer of 1:32 to 1:128.
Management[1,5,7 ]
Rh-D Negative Unsensitized PatientsFor prevention of sensitization:
- Rh-immune globulin(RhIgG)* 300 mcg (300 mcg covers 15 ml fetal cells) is given at 28 weeks' .
- Postpartum if the antibody screen is negative a second dose of RhIgG is given if the infant is Rh-positive or Du-positive.
*Rh-immune globulin is an antibody that will help to remove any Rh positive cells in the mother's blood. Rh-immune globulin must be given before the mother begins to produce her own antibody to the Rh factor.
In general the priniciples used in the management of the Rh-D negative sensitized patient and the management of the patient with atypical blood antibodies do not differ.
Previously Affected Pregnancy
If the father is Rh negative (or negative for the atypical antigen) then no further testing is necessary. IAT titers of < 1:32 or less are managed noninvasively with repeat antibody titers every 2-4 weeks. IAT > 64 amniocentesis q 2 to 3 weeks. IAT titers of > 1:32 with pregnancies at greater than 27 week are usually monitored with serial amniocentesis If the father is heterozygous (Dd) or his blood is unavailable then PUBS or amniocentesis may be used to determine the fetal Rh (or atypical antigen) status if the IAT titer is > 1:32 or albumin titer > 1:16. Fetal DNA testing is available for:
- RhD, RhE, Rhc, RhC, and Kell.
( Send 5.0 ml of fluid in a unbreakable sterile plastic conical -bottom centrifuge tube. DO NOT FREEZE)- For RhE, Rhe, RhC, Rhc, Kell ,and Cellano (k) the parents' DNA should be tested concurrently (Send 5.0 ml of blood in a lavender-topped tube on each parent. DO NOT FREEZE)
- If the fetus is antigen negative then no further testing is necessary.
- If the fetus is antigen positive then the pregnancy is followed with serial titers and ultrasound as long as titers remain below the "critical" value.
For patients with a previously affected pregnancy, the timing of the initial procedure is determined by past clinical history. It is usually performed at least 4-8 weeks earlier than the prior gestational age at which significant morbidity occurred.
Surveillance Serial Amniocentesis
Fetuses affected by hemolytic disease secrete abnormally high levels of bilirubin into
the amniotic fluid. The amount of bilirubin can be quantitated by
spectrophotometrically measuring absorbance at the 450-nm wavelength in a
specimen of amniotic fluid that has been shielded from light.
Alternatively, percutaneous umbilical blood sampling (PUBS) may be used
to determine all blood parameters directly.
If amniocentesis is used to monitor the fetus, the results (delta 450) are plotted on a "Liley" curve.
If amniocentesis is used to monitor the fetus, the results (delta 450) are plotted on a "Liley" curve.
The Liley Curve
The Liley curve is divided into three zones.
Patients with results in zone I or low zone II can
be allowed to proceed to term, at which point labor should be induced.
In most cases, patients in the middle of zone II can progress to 36-38
weeks of gestation. Depending on gestational age, patients in zone III
should either be delivered or should receive intrauterine fetal
transfusion.
Although serial determinations of Delta optical density at 450 nm and
PUBs are the most common methods for the evaluation of fetal status,
Doppler ultrasonography of the middle cerebral artery has also been used
to identify fetuses at risk for moderate to severe hemolytic disease.
Expected Peak Velocity of Systolic Blood Flow through MCA (calculator) [9, 10]
Tranfusion Protocol (calculator)
Lastly, in women with extremely high titers ( > 256), at less
than 28 weeks, where the fetus does not demonstrate hydrops, and there
is a documented history of fetal death due to hydrops intravenous immune
serum globulin (IVIG) might be offered.
The dose is 400 mg/kg per day for 5 days, with repeat infusions every 15
to 21 days.
Specific contraindications to intravenous immunoglobulin
use include a previous episode of intravenous immunoglobulin-induced
anaphylaxis (rare) and selective
IgA deficiency. [12, 13]
REFERENCES
1. American College of Obstetricians and Gynecologists. Management of Isoimmunization in Pregnancy ACOG Technical Bulletin 227. Washington, DC: ACOG, 1996
2. Race RR. The Rh genotype and Fisher's theory. Blood (Special Issue No 2) 1948;3:27
3. Masouredis SP:Realtionship between Rho(D) genotype and quantitiy of I131 anti-Rho(D) bound to red cells. J Clin Invest 39:1450,1960
4. Lacey PA et al. Fatal hemolytic disease of the newborn due to anti-D in anRH positive Du variant mother. Transfusion 1983;23:91
5. John M Bowman. Maternal Alloimmunization and Fetal Hemolytic Disease. In: Reece EA et al (eds), Medicine of the Fetus and Mother.Philadelphia ,J.B Lippincott, 1992.
6.Bergstrom H et al. :Demonstration of Rh antigens in a 38-day-old fetus. Am J Obstet Gynecol 99:130,1967.
7.Michael L. Socol. Management of Blood Group Isoimmunization. In: Gleicher N et al (eds), Principles and Practice of Medical Therapy in Pregnancy.New York , Appleton & Lange, 1998.
8. Copel JA, Scioscia A, Grannum PA, Romero R, Reece EA, Hobbins JC. Related Articles Percutaneous umbilical blood sampling in the management of Kell isoimmunization. Obstet Gynecol. 1986 Feb;67(2):288-90.
9. Collaborative Group for Doppler Assessment of the Blood Velocity in Anemic Fetuses. N Engl J Med. 2000 Jan 6;342(1):9-14.
10. Mari G, Adrignolo A, Abuhamad AZ, et al. Diagnosis of fetal anemia with Doppler ultrasound in the pregnancy complicated by maternal blood group immunization. Ultrasound Obstet Gynecol 1995;5:400-5.
11. Liley AW. Liquor amnii analysis in management of pregnancy complicated by rhesus immunization. Am J Obstet Gynecol 1961;82:1359
12. Margulies M, Voto LS, Mathet E, Margulies M. High-dose intravenous IgG for the treatment of severe rhesus alloimmunization. Vox
Sang 1991;61:181-9.
13. Porter TF, et al Intravenous immune globulin in the management of severe Rh D hemolytic disease.Obstet Gynecol Surv. 1997;52:193-7.
Resources:
- The Rhesus Site
-
Rh
Disease
(Kenneth J. Moise,MD) -
Rh isoimmunization
2002 Contemporary OB/GYN - OMIM Entry
The article is reproduced in accordance with Section 107 of title 17 of the Copyright Law of the United States relating to fair-use and is for the purposes of criticism, comment, news reporting, teaching, scholarship, and research.
2 comments:
RH- for E or C? How would you know? I have heard of C+ Heamolytic disease though.
RH- E C? I have heard of C+? haemolytic disease though.
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