Human genome-wide association studies have indicated that a common single nucleotide sequence variant influences the size and number of red blood cells. A team led by Harvey Lodish of the Whitehead Institute, and Eric Lander of the Broad Institute, both in Cambridge, Massachusetts, found that this variant in the non-coding sequence reduces the expression of the nearby gene CCND3, which is involved in controlling the cell cycle.

Reducing the expression of the gene in human and mouse red-blood-cell precursors caused the cells to go through fewer divisions, resulting in fewer, but bigger, red blood cells.

Genes Dev. http://dx.doi.org/10.1101/gad.197020.112 (2012)