Simone Jung | bioRxiv Science

bioRxiv2016

A missense mutation in TUBD1 is associated with high juvenile mortality in Braunvieh and Fleckvieh cattle

BackgroundHaplotypes with reduced or missing homozygosity may harbor deleterious alleles that compromise juvenile survival. A scan for homozygous haplotype deficiency revealed a short segment on bovine chromosome 19 (Braunvieh haplotype 2, BH2) that was associated with high juvenile mortality in Braunvieh cattle. However, the molecular genetic underpinnings and the pathophysiology of BH2 remain to be elucidated.\n\nResultsThe frequency of BH2 was 6.5 % in 8,446 Braunvieh animals from the national bovine genome databases. Both perinatal and juvenile mortality of BH2 homozygous calves were higher than the average in Braunvieh cattle resulting in a depletion of BH2 homozygous adult animals (P=9.3x10-12). The analysis of whole-genome sequence data from 54 Braunvieh animals uncovered a missense mutation in TUBD1 (rs383232842, p.H210R) that was compatible with recessive inheritance of BH2. The availability of sequence data of 236 animals from diverse bovine populations revealed that the missense mutation also segregated at a low frequency (1.7 %) in the Fleckvieh breed. A validation study in 37,314 Fleckvieh animals confirmed high juvenile mortality of homozygous calves (P=2.2x10-15). Our findings show that the putative disease allele is located on an ancestral haplotype that segregates in Braunvieh and Fleckvieh cattle. To unravel the pathophysiology of BH2, six homozygous animals were examined at the animal clinic. Clinical and pathological findings revealed that homozygous calves suffered from chronic airway disease possibly resulting from defective cilia in the respiratory tract.\n\nConclusionsA missense mutation in TUBD1 is associated with high perinatal and juvenile mortality in Braunvieh and Fleckvieh cattle. The mutation is located on a common haplotype likely originating from an ancient ancestor of Braunvieh and Fleckvieh cattle. Our findings demonstrate for the first time that deleterious alleles may segregate across closed cattle breeds without recent admixture. Homozygous calves suffer from chronic airway disease resulting in poor growth performance and high juvenile mortality. The respiratory manifestations resemble key features of diseases resulting from impaired function of airway cilia.

Genomics↗

bioRxiv2016

A frameshift mutation in GON4L is associated with proportionate dwarfism in Fleckvieh cattle

BackgroundLow birth weight and postnatal growth restriction are the most evident symptoms of dwarfism. Accompanying skeletal aberrations may compromise the general condition and locomotion of affected individuals. Several paternal half sibs with low birth weight and size were born in 2013 in the Fleckvieh cattle population.\n\nResultsAffected calves were strikingly underweight at birth despite a normal gestation length and had craniofacial abnormalities such as elongated narrow heads and brachygnathia inferior. Despite a normal general condition, their growth remained restricted during rearing. We genotyped 27 affected and 10,454 unaffected animals at 44,672 SNPs and performed association testing followed by homozygosity mapping to map the growth failure to a 1.85 Mb segment on bovine chromosome 3. Analysis of whole-genome re-sequencing data from one affected and 289 unaffected animals revealed a 1bp deletion (g.15079217delC, rs723240647) in the coding region of the GON4L gene that segregated with the dwarfism-associated haplotype. We show that the deletion introduces intron retention and premature termination of translation, putatively resulting in a severely truncated protein that lacks domains that are likely essential to normal protein function. The widespread use of an unnoticed carrier bull for artificial insemination has resulted in a tenfold increase in the frequency of the deleterious allele in the female population.\n\nConclusionsA frameshift mutation in GON4L is associated with autosomal recessive proportionate dwarfism in Fleckvieh cattle. The mutation has segregated in the population for more than fifty years without being recognized as a genetic disorder. However, the widespread use of an unnoticed carrier bull for artificial insemination caused a sudden accumulation of homozygous calves with dwarfism. Our findings provide the basis for genome-based mating strategies to avoid the inadvertent mating of carrier animals and thereby prevent the birth of homozygous calves with impaired growth.

Genomics↗