OTC and ornithine carbamoyltransferase deficiency: The well-known OTCD model animals, sparse-fur (spf/1) mice (ID156, Balb/c background spontaneous mutation mice) show 1/6 the level of OTC activity (wild-type mice: 317.8 ± 51.5 nmol/min/mg, OTCD mice: 53.7 ± 33.5 nmol/min/mg, [mean ± SD, n = 3], unpublished data) and survive for approximately two months (median, 47 days; range: 20–52) [5,10].