A Genome-wide Scan of red cell indices replicates linkage on chromosome 6q23-24

Anastasia Iliadou ¹, David M Evans ^2*, Gu Zhu ³, David L Duffy ³, Ian H Frazer ⁴, Grant W Montgomery ³ and Nick G Martin ³

¹ Karolinska Institutet, Sweden
² Wellcome Trust Centre for Human Genetics, University of Oxford, United Kingdom
³ Queensland Institute of Medical Research, Australia
⁴ University of Queensland, Australia

^* To whom correspondence should be addressed. E-mail: davide{at}well.ox.ac.uk.

Accepted 24 August 2006

Abstract

Background: The red cell indices quantify the size, number and oxygen-carrying ability of erythrocytes. Whilst the genetic basis of many monogenic forms of anemia is well understood, comparatively little is known regarding the genes responsible for variation in the red cell indices among healthy individuals.

Objective: To identify quantitative trait loci responsible for normal variation in the red cell indices of 391 pairs of dizygotic twins who were measured longitudinally at ages twelve, fourteen and sixteen.

Results: We found suggestive evidence of linkage to haemoglobin concentration (LOD = 3.03) and hematocrit (LOD = 2.95) on chromosome 6q23, a region previously identified as possibly harboring a QTL for haematocrit. We also found suggestive linkage to several other regions of the genome including chromosome 4q32 for red cell count and 7q for mean cell volume. In contrast, there was little evidence of linkage to the chromosomal regions containing the genes for erythropoietin (7q22) and its receptor (19p13.2), nor to the regions containing the genes for the haemoglobin alpha (16p13.3) and beta chains (11p15.4).

Conclusion: Our findings provide additional evidence for a QTL affecting haemoglobin and haematocrit on chromosome 6q23. In contrast, polymorphisms in the genes coding for erythropoietin, its receptor and the haemoglobin alpha and beta chains do not appear to contribute substantially to variation in the red cell indices between healthy individuals.

Keywords: blood cell count, erythrocyte, genetics, linkage, twins

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