Both hypopituitary Ames dwarf mice, homozygous for the hypomorphic df point mutation allele of the prophet of Pit1, paired-like homeodomain transcription factor (PROP paired-like homeobox 1) (Prop1df) gene, which are deficient in growth hormone (GH) production, and Laron syndrome-modeling growth hormone receptor/binding protein (Ghr/bp) gene-disrupted (GHR-KO) mice are shorter and lighter than their littermate controls. This evidence concerns the gene GHR and Down syndrome.