Protection Afforded by Sickle-Cell Trait (Hb AS): What Happens when Malarial Selection Pressures Are Alleviated?

Document Type

Article

Authors

Charles Hoff, Department of Pediatrics, School of Medicine, University of Utah, Salt Lake City, UT.
Ian Thorneycroft, Department of Obstetrics and Gynecology, College of Medicine, University of South Alabama, Mobile, AL.
Felicia Wilson, Department of Pediatrics, College of Medicine, University of South Alabama, Mobile, AL.
Monica Williams-Murphy, COM III Medical Program, College of Medicine, University of South Alabama, Mobile, AL.

Abstract

A study of reproductive outcome in Mobile, AL was conducted among a large maternal cohort with sickle-cell disease (Hb SS), sickle-cell trait (Hb AS), and no hemoglobinopathies (Hb AA). It was found that mean gravidity and live births among Hb AS women were significantly higher than among Hb AA women. These findings were surprising since it is generally held that once malarial pressure is alleviated, any reproductive advantage that might be conferred by Hb AS would disappear and fertility levels would reach levels similar to or slightly less than that of Hb AAwomen. Asearch of the literature was subsequently conducted and a large cohort study of an African- derived population was found in the United Kingdom. Results from this study also showed that parity was significantly higher among Hb AS women compared to Hb AA women. If survivorship is similar among Hb AS and Hb SS women, findings from these two studies raise doubts whether directional selection is occurring against the Hb S allele in nonmalarial environments. Balancing selection may still be occurring.

Recommended Citation

Hoff, Charles; Thorneycroft, Ian; Wilson, Felicia; and Williams-Murphy, Monica (2001) "Protection Afforded by Sickle-Cell Trait (Hb AS): What Happens when Malarial Selection Pressures Are Alleviated?," Human Biology: Vol. 73: Iss. 4, Article 8.
Available at: https://digitalcommons.wayne.edu/humbiol/vol73/iss4/8