Rhesus factor (RhD) DNA test in men
What is rhesus factor (RhD)?
Rhesus factor depends on the presence or absence of a protein—Rhesus D antigen (RhD)—on the surface of erythrocytes (red blood cells). If rhesus D antigen is present on the surface of erythrocytes, the person is rhesus positive: RhD+, but if there is no rhesus D antigen, the person is rhesus negative: RhD-.
What determines if a person is rhesus positive or negative?
The human rhesus factor is determined by the gene RHD, the product of which is a protein: the RhD antigen. Humans have two sets of chromosomes: one inherited from their mother and one from their father, meaning that each of our cells has two copies of the RHD gene, the so-called alleles. If both copies function and produce the RhD antigen, the human is rhesus positive-homozygous, whereas if only one copy is active: rhesus positive-heterozygous. In rhesus-negative people, both RHD alleles of the gene are non-functional, and the RhD antigen is not produced or is inactive.
What is rhesus factor incompatibility?
Rhesus factor incompatibility occurs when a rhesus-negative person, who does not have the rhesus D antigen, receives erythrocytes of rhesus-positive blood with the rhesus D antigen. As a result, the rhesus D antigen is recognized as a foreign body, and antibodies are formed against it.
Rhesus factor incompatibility can lead to complications both after a blood transfusion and during pregnancy. During pregnancy, rhesus incompatibility may occur when the woman is rhesus-negative, but the biological father of the unborn child is rhesus-positive: there is a possibility that the foetus may be rhesus-positive, resulting in antibodies to the foetal antigen RhD in the pregnant woman’s blood.
During the first pregnancy, antibodies are rare and the baby is usually healthy. The risk of complications increases with each subsequent pregnancy. Rhesus antibodies interfere with foetal development, may lead to premature birth or neonatal haemolytic disease.
What is the probability that the foetus could be rhesus positive if the DNA status of the father’s rhesus factor (RhD) (homozygous or heterozygous) is known?
If the father of the unborn child is homozygous (both the RHD alleles of the gene are functional), then the foetus will definitely be rhesus positive. It also means that all children of this man will be rhesus positive — whether the child’s mother is rhesus positive or not. If in this case the pregnant woman is rhesus negative, she will need additional treatment.
If the father of the unborn child is heterozygous (one of his two RHD alleles is functional), there is a 50% chance that the foetus may be rhesus positive and a 50% chance that the rhesus factor is negative. In such cases, it would be advisable for a rhesus-negative woman to check the rhesus status of the foetus (positive or negative) during each pregnancy.
In which cases rhesus-positive men should have a rhesus factor (RhD) DNA test?
If the female partner is rhesus negative and the male partner is rhesus positive. With this test, it is possible to determine whether the planned children will be 100% rhesus positive or be rhesus negative with a likelihood of 50%.
Test description.
Rhesus factor testing for men is a completely safe procedure. For the purposes of the test, a swab from the oral mucosa, the so-called “saliva sample”, or a blood sample from a peripheral vein is collected. The DNA test for rhesus factor (RhD) status in men involves the relative quantification of two fragments of the RHD gene.