1. Determining the Frequency of the Cartwright Blood Group Antigens in the Maltese Population
Gabrielle Sant, B.Sc. (Hons) in Applied Biomedical Science, intake 2012
Abstract
Methods and Materials
The Cartwright (Yt) blood group system consists of the high incidence Ytᵃ antigen and the low incidence Ytᵇ antigen. Through this study the genetic frequency of the two antigens in the Maltese population was calculated. Although the Yt antigens have variable clinical significance, delayed haemolytic transfusion reactions have been recorded due to allo-antibodies directed towards the antigens of this blood group system. Knowledge of the antigen frequency is important to assess the risk of antibody formation and to calculate the probability of finding antigen-negative blood in a random donor population. The molecular genotype that is able to determine the presence and absence of the expressed Yt antigens in around 400 neonatal cord blood DNA samples was determined using Yt allele specific primers. The genotyping process identified at the molecular level, the polymorphism responsible for the missense mutation (p.His353Asn) that distinguishes the two antigens. The data allows for a future registry of molecular blood group antigen results and ought to serve in cases when rare blood type transfusions are requested and serve its purpose to the local community on the Maltese Islands.
405 anonymous Maltese DNA samples extracted from neonatal cord blood samples were used for this study. The DNA samples were present at the Malta Bio Bank, located at the Laboratory of Molecular Genetics, University of Malta, on Campus.
Quality checks were performed on a number of the DNA samples. Some samples were quantified by NanoDrop™ spectrophotometry followed by agarose gel electrophoresis to assess the DNA’s integrity.DNA was analysed for the Ytᵃ and Ytᵇ alleles using Allele Specific Primer Extension (ASPE) Polymerase Chain Reaction (PCR). The Human Growth Hormone (HGH) gene was used as an internal control. The PCR products were analysed by Agarose-Gel electrophoresis.
Introduction
Figure 2. PCR products as seen after a run on 1.5% agarose gel.  this figure is adapted between the work of two parallel projects involving the genotyping of the Cartwright antigen conducted by Ms. Rebecca Spiteri
Graph 1. Cartwright Blood Group Genotype Frequencies and Gender Proportions in the Study Population.
The Cartwright blood group system (ISBT: 011) is coded by a gene found on chromosome 7 position 7q22.1. This gene is known as the ACHE gene and codes for acetylcholinesterase, an enzyme which is essential for normal cholinergic neurotransmission. A single nucleotide polymorphism on the acetylcholinesterase gene results in the two different antigens Ytᵃ and Ytᵇ. These antigens are found in very different frequencies in different ethnicities and countries.
Figure 1. Cytogenetic Location of the ACHE gene: 7q22, which is on the q arm of chromosome 7 at position 22
Cases of allo-antibodies anti-Ytᵃ and anti-Ytᵇ have been reported to be produced on exposure to the antithetical antigen (either through transfusion or pregnancy). These antibodies have a varying clinical significance as there have been reported to cause haemolytic transfusion reactions of varying severity. These antibodies/antigens are not tested for in pre-transfusion serology testing but have been detected in Malta due to incompatible serology testing in the pre-transfusion stage.
Results
Discussion
The results obtained were used to determine the frequency of the Ytᵃ and Ytᵇ blood group antigens in the Maltese population. These were compared to the frequencies in other populations as described in other published studies.
The Yta (frequency: ) and Ytb (frequency: ) frequencies obtained in this study are very similar to those observed in western countries. However when comparing the results to data obtained from other studies, the Maltese Yta gene frequency was found to be slightly lower to the other calculated frequencies. This was due to the relatively high number of heterozygous samples identified throughout the study. Out of the 405 samples tested, 46 were found to be heterozygous. This caused the Yta gene frequency to lower slightly.
This study has confirmed that the Cartwright blood group genotype amongst the Maltese population follows the general molecular demographic data of other European countries, and in contrast to middle to far eastern countries.
Out of the 405 samples tested the majority of samples were found to be Yta homozygous (88.4%) as was expected. There were 46 heterozygous samples (11.4%) and a single Ytb sample (excluding the known Ytb positive samples used as controls) was found (0.2%) within the study population.
The results were found to be in Hardy Weinberg Equilibrium.
The study population was also split by gender and the Hardy Weinberg Equilibrium was done on both genders so as to see whether there were any discrepancies
Frequency in the Maltese population
Expected
Observed
Yta+
358.42
358
Ytb+
1.42 1
Yta+b+
45.16 46
Table 1. The expected and observed frequencies obtained
References
Contact
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Gabrielle Sant
University of Malta
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