Vel blood group

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Small integral membrane protein 1 (Vel blood group antigen)
Identifiers
SymbolSMIM1
Chr. 1 p36.32
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StructuresSwiss-model
DomainsInterPro

The Vel blood group is a human

antibodies when exposed to Vel-positive blood, which can cause transfusion reactions on subsequent exposures.[2]

Genetics

Autosomal recessive inheritance

The Vel blood group is associated with the SMIM1 gene, which is located in the 1p36 region of

single nucleotide polymorphisms in the noncoding regions of SMIM1 affect the strength of Vel antigen expression.[5]

Epidemiology

The Vel-negative blood type is rare. The highest prevalence of Vel-negative blood has been reported in Sweden, where approximately 1 in 1200 individuals exhibit this phenotype.[5] Only about 1 in 3000 English people[8] and 1 in 4000 Southern Europeans are Vel-negative, and much lower rates have been reported in people of African and Asian heritage.[5]

Clinical significance

Patients with anti-Vel antibodies require rare Vel-negative donor blood, or may self-donate before elective surgery that calls for a blood transfusion.

When exposed to Vel-positive blood through

autologous blood donation or to contact rare blood banks.[12]

Cases of anti-Vel causing

IgM immunoglobulin, which does not cross the placenta into the fetal circulation.[9]: 981  In addition, the expression of Vel is very weak on fetal red blood cells – particularly in children who are heterozygous for Vel.[8]

Autoimmune hemolytic anemia (a condition in which patients produce antibodies against antigens on their own red blood cells, leading to hemolysis)[9]: 956  involving auto-anti-Vel has been reported.[8]

Laboratory testing

An individual's Vel blood type can be determined by

polyclonal antibodies isolated from the blood of patients with anti-Vel. However, this method is problematic because these antibodies are variable in quality and sometimes produce false negative results in patients with weak Vel expression; moreover, the reagent cannot be mass-produced.[5][13] In 2016, a recombinant monoclonal antibody against Vel was introduced[14] and it has since been used to screen for Vel-negative blood donors in France.[5] Genotyping of SMIM1 using polymerase chain reaction is another method that has been used to identify Vel-negative donors.[15]

Anti-Vel is a mixture of

cold antibody in compatibility testing if inappropriate techniques are used; this misidentification is dangerous, because such antibodies are usually clinically insignificant.[5][12][17]

History

The Vel blood group was first described in 1952 by Sussman and Miller,

crossmatched against blood samples from 10,000 donors, and only five of them were found to be compatible, indicating that an antibody against a high-frequency antigen was present.[5] This antigen was named Vel after the first patient.[1] The authors also observed variable expression of the antigen: the patient's serum reacted less strongly with the blood of her children, who were presumably heterozygous for Vel, than with blood from unrelated donors.[5]

In 1955, a further case was described [19] in which the blood of a woman who had suffered a transfusion reaction was incompatible with more than 1,000 donors, but not with the blood of the first Vel-negative patient.[5] This patient's antibody was the first example of an anti-Vel that could hemolyze red blood cells in vitro.[20] Six other individuals from three generations of this woman's family were found to be Vel-negative, but they did not exhibit an anti-Vel antibody, demonstrating that anti-Vel is not naturally occurring.[2] By 1962, 19 cases of anti-Vel and approximately 50 cases of Vel-negative patients had been described.[20]

Although the Vel blood group has been widely studied due to its significance in transfusion medicine, its genetic and molecular basis remained unclear for several decades.[12][14] In 2013, two research groups simultaneously identified the SMIM1 gene and its protein product as the determinants of the Vel blood group.[12][3][4] The Vel blood group was officially recognized by the International Society of Blood Transfusion in 2016.[7]

References