Q: I have type A Rh positive Anti K blood type. I am trying to find more information concerning the anti-K issue. From what little information I am able to gather it is linked to 2 recessive genes, the K is passed to the fetus from the father & during a fetomaternal bleed the fetus exposes the mother to the antigen in turn causing the mother to produce an antibody. My biggest concern is what does being K positive for my daughter mean? Does it mean if she and her mate are both K positive, then their offspring would be prone to neuromuscular problems such as McLeods or muscular dystrophy? From the limited information I have been able to attain it does point to this issue. Can you please shed some light on this for me?

A:The Kell blood group is one of the major antigenic systems in human red blood cells and is important in transfusion medicine because the antibodies can cause severe reactions to transfusion of incompatible blood and haemolytic disease in newborn infants (HDN). It consists of over 20 different antigens (KEL1 to KEL24), which are coded by a gene complex present on chromosome 7. The k antigen (Cellano or K2) is far more common than K antigen (Kell or K1). Approximately 9% of the population has the K1 RBC phenotype and antibodies to K1 are developed in about 5% of persons receiving a single unit of incompatible blood. Kell antibodies are about 60% as frequent as Rh (D) antibodies, but Kell disease is only 3% as common as Rh haemolytic disease. The reason is related to frequent transfusion-alloimmunisation by Kell antigen and the low frequency of the K:1 gene among fathers. Kell haemolysis is severe in about half of cases. The K (K1) antigen is very immunogenic and causes strong reactions in case of mismatched blood transfusion and severe fetal anaemia in sensitised mothers. It is produced only after exposure to the antigen as a result of pregnancy or repeated blood transfusions and thus the anti-K antibody is seen frequently in individuals. The k antigen (K2) too is immunogenic but as it is present in most individuals, the anti-k antibody is much less common. Kell antigen expression on the RBCs is dependent on the expression of a protein called XK protein (whose gene is present on the X chromosome). As XK is complexed with Kell through a disulfide bond, XK is often considered a component of the Kell blood group system even though Kell and XK are proteins of two different genes. Kell null phenotype (K0) is the complete lack of all known Kell antigens on red cells. Kell null is found at a very low frequency in all population groups. The McLeod phenotype is the absence of XK protein and this is associated with unique red blood cell morphology (acanthocytosis), haemolytic anaemia, and late onset forms of muscular dystrophy and cardiomyopathy. Also, neurological defects are common. This phenotype is also associated with a disease called X-linked chronic granulomatous disease. The majority of cases of Kell sensitisation are secondary to incompatible red cell transfusions since blood is not routinely cross matched for the Kell antigen. In the case of the Kell antigen, 92% of males will be Kell negative; only Kell negative, unaffected offspring can therefore be expected if these individuals father a child. For this reason, Kell typing of the father is the primary step in the management of Kell disease in pregnancy. The remaining 8% of males will be Kell positive; 98% of these will be heterozygous while 2% will be homozygous. If the father is Kell-positive and the maternal anti-Kell indirect antiglobulin titre is 8 or greater, amniocentesis should be performed at 16-20 weeks' gestation. PCR assays for the determination of K1/K2 status of an individual are available and these tests provide accurate and timely information that can aid the prenatal care of women sensitised to Kell antigens where the fetus is at risk for haemolytic disease of the newborn due to anti-K.