Embryonic mortality attributed to inherited deficiency of uridine monophosphate synthase

The deficiency of uridine-5'-monophosphate synthase is inherited as an autosomal recessive trait in Holstein-Friesian cattle. Heterozygotes are characterized by half normal activity of uridine monophosphate synthase, as measured in erythrocytes. Matings between heterozygotes for the deficiency have produced 31 pregnancies lasting at least one month, but only 23 full-term calves, including 9 homozygous normal and 14 heterozygotes. That the eight embryos were not carried to term is consistent with the probability of a homozygous-deficient genotype and are lost around 40 d of gestation. Although the homozygous deficiency of uridine monophosphate synthase is lethal embryonically in cattle, homozygotes for the analogous human condition have been born alive.