this function of the ci-mpr was determined through the use of knockout mice. it was observed that ci-mpr deficient mice had an increased level of free igf-ii and enlarged organs (around a 30% increase in size ). these mice die at day 15 of gestation due to cardiac hyperplasia. death of the mice could be prevented when the igf-ii allele was also knocked out. when the ci-mpr and the igf-ii allele are knocked out normal mouse growth is observed as there is no longer a growth factor present that needs to be regulated.