Hereditary xanthinuria in a goat

A 2-year-old mixed breed goat was presented for a 1-day history of anorexia and 1 week of weight loss. Serum biochemistry disclosed severe azotemia. Abdominal ultrasound examination showed decreased renal corticomedullary distinction, poor visualization of the renal pelves, and dilated ureters. On necropsy, the kidneys were small, the pelves were dilated, and the medulla was partially effaced by variably sized yellow nephroliths. Histologically, cortical and medullary tubules were distended by yellow-brown, multilayered crystals. Stone composition was 100% xanthine. Exonic sequencing of xanthine dehydrogenase (XDH) and molybdenum cofactor sulfurase (MOCOS) identified 2 putative pathogenic variants: a heterozygous XDH p.Leu128Pro variant and a homozygous MOCOS p.Asp303Gly variant. Variant frequencies were determined in 7 herd mates, 12 goats undergoing necropsy, and 443 goats from genome databases. The XDH variant was not present in any of these 462 goats. The MOCOS variant allele frequency was 0.03 overall, with 3 homozygotes detected. Hereditary xanthinuria is a recessive disorder in other species, but the XDH variant could be causal if the case goat is a compound heterozygote harboring a second variant in a regulatory region not analyzed or if the combination of the XDH and MOCOS variants together abolish XDH activity. Alternatively, the MOCOS variant alone could be causal despite the presence of other homozygotes, because hereditary xanthinuria in humans often is asymptomatic. Ours is the first report describing the clinical presentation and pathology associated with xanthine urolithiasis in a goat. The data support hereditary xanthinuria, but functional studies are needed to conclusively determine the causal variant(s).

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.

DUMPS cattle carry a point mutation in the uridine monophosphate synthase gene

Deficiency of uridine monophosphate synthase (DUMPS) is a monogenic autosomal recessive disorder in cattle, resulting in early embryonic death of homozygous offspring. To identify the mutation responsible for DUMPS, liver RNA from identified, DUMPS heterozygous animals from the Holstein and Red Holstein breeds was reverse transcribed. Amplification of cDNA with sequence-specific primers and subsequent sequencing of the PCR products revealed a mutation (C-->T) with the loss of an AvaI site at codon 405, resulting in a premature stop codon with a truncated C-terminal catalytic subunit of the protein. A direct DNA test based on PCR was developed and subsequently tested on 102 animals. Complete concurrence of deficiency of UMPS and the presence of the described point mutation in heterozygous animals was observed, thus confirming this point mutation as the basic defect in DUMPS cattle.