Genetic Testing for TMEM154 Mutations Associated with Lentivirus Susceptibility in Sheep

Ovine lentiviruses cause incurable, progressive, lymphoproliferative diseases that affect millions of sheep worldwide.  Genetic variation in the ovine transmembrane protein 154 gene (TMEM154) has been recently associated with lentivirus infections in U.S. sheep.  Sheep with the two most common TMEM154 alleles encoding E35 were highly-susceptible compared to homozygous sheep with the K35 missense mutation.  Our overall aim was to estimate the distribution of highly-susceptible TMEM154 haplotypes in sheep from around the world and develop a genetic test for selecting breeding stock with reduced susceptibility to ovine lentivirus.  The frequency of TMEM154 E35 alleles among 74 breeds was 0.51 and indicated that highly-susceptible variants were present in breeds around the world.  Analysis of TMEM154 in whole genome sequence data from an international panel of 75 sheep revealed 1,387 previously unreported polymorphisms in a 62 kb region and confirmed that highly-susceptible haplotypes (designated 2 and 3) were distributed worldwide.  Four polymorphisms were novel missense mutations in either the signal peptide (A13V) or the extracellular domain (E31Q, I74F, and I102T) of TMEM154.  A matrix-assisted laser desorption/ionization—time-of-flight mass spectrometry assay was developed to detect the ten missense and two deletion mutations.  In blinded trials, the call rate for the eight most common coding polymorphisms was 99.4% for 499 sheep tested and 96.0% of the animals were assigned paired TMEM154 haplotypes (i.e., diplotypes).  The widespread distribution of highly-susceptible TMEM154 alleles suggests that genetic testing and selection may improve the health and productivity of infected flocks.