Mapping the Genetic Cause of Agnathia in Sheep
Abstract: Agnathia is a lethal malformation characterized by complete or partial absence of the lower jaw. Agnathia can be accompanied by microstomia (small mouth) and aglossia (absence of the tongue).
This complex malformation can be attributed to both genetic and teratogenic causes. Recently, a population of domestic sheep (Ovis aries) began reporting occurrences of lambs missing the lower jaw at birth to the National Sheep and Goat Defect Registry at Tarleton State University. The condition appears to be lethal at birth, as the lambs struggle to breathe and die within minutes. Necropsies of three affected lambs indicated that the trachea and esophagus were underdeveloped, and cause of death was determined to be asphyxiation due to the missing tongue. Pedigree analysis indicated high levels of inbreeding among the affected lambs, with one particular common ancestor on both sides of the affected families. Hair or tissue samples from three affected lambs as well as family members and other sheep within the breed were collected for DNA and pedigree. DNA was purified and twelve sheep were submitted for 600K Sheep HD SNP chip genotyping (Ag Research, Neogen). Genotypes were analyzed for homologous overlap of affected lambs using PLINK software. Based on SNP chip analysis for homozygosity in affected lambs, the causative region of agnathia in sheep was narrowed down to three possible regions: 105kb on sheep Chromosome 5 (OAR5) and two regions on OAR4 ranging 168kb and 81kb in length. Over 150 more DNA samples have been collected and genotype verification assays by qPCR melt curve analysis are currently underway to narrow these suspect regions to one causative allele. A definitive marker test will be made available to sheep producers as soon as all verifications are complete.
Kristen McDaniel*, Luke Kramer, Sierra Long, Taylor Karr, Brant Poe, James Reecy, and Jolena Waddell
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