Technical Report No. 8-89
Frequency of variant erythrocytes at the glycophorin A locus in two Bloom’s syndrome patients
Kyoizumi S, Nakamura N, Takebe H, Tatsumi K, German J, Akiyama MEditor’s note: A publication based on this report was published in Mutat Res 214:215-22, 1989.
Summary
Blood type MN is determined by a glycoprotein called glycophorin A (GPA), which exists on the surface of erythrocytes, and the difference between the M and N types is derived from the presence of two different amino acids at the amino terminal portion. Using a pair of fluorescence-labeled monoclonal antibodies specific to each GPA, somatic mutations in erythrocytes of MN heterozygotes at the GPA-M and -N alleles can be quantitatively determined by a flow sorter. Our results for two Bloom’s syndrome (BS) patients showed that variants either lost expression of one allele (simple gene inactivation or loss) or expressed only one allele at twice the normal level (most probably somatic recombination), occurring at a frequency of about 1-3 per 103 erythrocytes. The flow cytometric patterns of erythrocytes from the BS patients showed a typical smear of variants bearing intermediate levels of expression of one GPA allele, indicating the real variant frequency is even greater than measured. On the other hand, the parents heterozygous for the BS gene showed variant frequencies which are within the normal range (1-8 x 10-5). These data strongly supported the hypothesis that cancer proneness of BS patients is due to their increased frequency of spontaneous mutations and somatic recombinations.
Blood type MN is determined by a glycoprotein called glycophorin A (GPA), which exists on the surface of erythrocytes, and the difference between the M and N types is derived from the presence of two different amino acids at the amino terminal portion. Using a pair of fluorescence-labeled monoclonal antibodies specific to each GPA, somatic mutations in erythrocytes of MN heterozygotes at the GPA-M and -N alleles can be quantitatively determined by a flow sorter. Our results for two Bloom’s syndrome (BS) patients showed that variants either lost expression of one allele (simple gene inactivation or loss) or expressed only one allele at twice the normal level (most probably somatic recombination), occurring at a frequency of about 1-3 per 103 erythrocytes. The flow cytometric patterns of erythrocytes from the BS patients showed a typical smear of variants bearing intermediate levels of expression of one GPA allele, indicating the real variant frequency is even greater than measured. On the other hand, the parents heterozygous for the BS gene showed variant frequencies which are within the normal range (1-8 x 10-5). These data strongly supported the hypothesis that cancer proneness of BS patients is due to their increased frequency of spontaneous mutations and somatic recombinations.