Congenital increased muscular tonus in a Holstein calf - how new molecular genetic techniques can shed light on previously undefinable rare diseases.. RM169

A two-week-old female calf was referred to the Clinic for Ruminants at the Vetsuisse Faculty, University of Bern, Switzerland, with difficulties to stand and muscle tremor since birth. As there was no knowledge of a genetic disease with similar clinical signs in cattle, we assumed a spontaneous de novo mutation and therefore we sequenced the entire genome of the affected animal.The obtained sequence reads were mapped to the current version of the cow reference sequence (UMD3.1/bosTau6) and the data was checked for deviations (variants) like SNPs, short insertions and deletions. A total number of 18 exclusive variants was found in the calf genome when compared to cattle genomes of the ongoing 1000 bull genome project. Following the assumption that the calf was carrier of a newly occurred mutation, we expected the causal mutation to be present in the calf and absent in the parents. Therefore, we screened the sire, dam and the affected offspring for the 18 remaining candidate variants by Sanger sequencing. Following which sequence variants present in the parents were excluded. Through this approach one single variant was left: A single nucleotide polymorphism (SNP) replacing a thymine by a guanine on bovine chromosome 5 at bp-position 65,787,153. It was clearly identified as a de novo mutation as it was absent in both parents, but present in the calf. Interestingly, this SNP situated in exon 13 of the myosin binding protein C, slow type (MYBPC1) gene at position 885 of the open reading frame (c.885T>G) and is predicted to lead to an amino acid exchange from leucine to arginine of the encoded MYBPC1 protein sequence at position 295 (p.Leu295Arg). More remarkably, the calf’s phenotype resembles the human distal arthrogryposis type 1 phenotype. In conclusion, we successfully identified the highly likely causative mutation for a very rare disease with only one case taking advantage of the most recent technologies.