Detection of the homozygous recessive genotype for deficiency of uridine monophosphate synthase by DNA typing among bovine embryos produced in vitro.

A PCR-based DNA test for the genetic defect resulting in the deficiency of uridine monophosphate synthase (DUMPS) was developed for embryonic cells to identify the homozygous recessive genotype. This genotype is usually lethal at about day 40 of gestation. Oocytes from a cow, heterozygous for DUMPS, were fertilized in vitro with spermatozoa from a DUMPS-carrier bull and cultured in vitro until the morula or blastocyst stage. Embryos were matured in vitro, fertilized and cultured according to a method established in our laboratory. Heminested PCR was performed and the genotype of twelve embryos were unambiguously determined by the Aval digestion of the PCR products. Among these embryos two individuals homozygous for the defective DUMPS allele (R405-->STOP) were detected. From the remaining ten embryos, four were homozygous and six were heterozygous for the normal allele. The observed distribution is close to the expected ratio of 1:2:1. These results further support the monogenic recessive inheritance of the defect.