title: Etiology of differences in hematocrit between males and females: sequence-based polymorphisms in erythropoietin and its receptor.
abstract: BACKGROUND
  Males have a higher hematocrit (Hct) than females. The cause of this gender-based difference is unclear. We sought to determine whether polymorphisms of the erythropoietin (EPO) gene or of its receptor (EPOR) explain this situation.
  
  
  METHODS
  We designed primers for the EPO and EPOR genes. Previously undescribed polymorphisms were found based on band migration on polyacrylamide gel, and when then sequenced. The distribution of these polymorphisms was studied in a population of 819 non-iron-deficient, healthy blood donors. To test the gender differences, analysis was done based on groups defined by Hct levels. The chi-square statistic was used to compare the frequency differences between groups, with P < .05 considered statistically significant.
  
  
  RESULTS
  We found previously reported polymorphisms in both the EPO and EPOR genes. Sequence analysis showed that the EPO polymorphism was due to a difference in the repeat copy number of the tetranucleotide cytosine adenine cytosine thymine (CACT) at position 2153. A previously undescribed 12th allele was found for the EPOR polymorphic site. Statistical analysis showed that the EPOR alleles, EPORA1 and EPORA10, were present at a significantly higher frequency in females than in males (P = .027 and P = .041, respectively), and EPOR5 was found less frequently in females than in males (P = .048). The allelic frequency of the EPO polymorphism was not significantly different by gender or Hct groups.
  
  
  CONCLUSIONS
  These results suggest that the variation of Hct level by gender may have a genetic basis. The sequence-based polymorphism for EPOR may be partly responsible for this gender-based variation in Hct level. These findings offer new clues to understanding Hct variation in the general population and to elucidating mechanisms of controlling Hct levels.
authors.affiliation: Department of Obstetrics and Gynecology, University of Iowa College of Medicine, 200 Hawkins Dr, Iowa City, IA 52242-1080, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Zeng
authors.forename: J
authors.initials: J
authors.lastname: Yankowitz
authors.forename: J A
authors.initials: JA
authors.lastname: Widness
authors.forename: R G
authors.initials: RG
authors.lastname: Strauss
mesh_terms: D000328:Adult; D000483:Alleles; D001782:Blood Donors; D016009:Chi-Square Distribution; D004591:Electrophoresis, Polyacrylamide Gel; D004921:Erythropoietin / Q000235:genetics*; D005260:Female; D005787:Gene Frequency; D008040:Genetic Linkage; D006400:Hematocrit; D006801:Humans; D008297:Male; D016133:Polymerase Chain Reaction; D018807:Polymorphism, Single-Stranded Conformational; D017467:Receptors, Erythropoietin / Q000235:genetics*
chemical_list: D017467:Receptors, Erythropoietin; D004921:Erythropoietin