Hypopituitarism has been reported in Snell dwarf (Pit1dw/dw) mice due to a loss-of-function mutation in the pituitary-specific factor 1 (Pit1) gene, also known as POU domain, class 1, transcription factor 1 (Pou1f1) gene, which is involved in the differentiation of a specific cell lineage of the anterior pituitary during ontogenesis. The gene discussed is POU1F1; the disease is hypopituitarism.