Mthfr-null mice are viable and born in the expected Mendelian ratio but exhibit reduced survival and a range of phenotypes, including slower growth, liver steatosis, altered brain histology, and behavioral abnormalities (Chen et al., 2001, Schwahn et al., 2003, Jadavji et al., 2015, Lawrance et al., 2011). Here, MTHFR is linked to fatty liver disease.