Identification of a Hypomorphic <i>FANCG</i> Variant in Bernese Mountain Dogs.

Bernese mountain dogs (BMDs), have an overall cancer incidence of 50%, half of which is comprised of an otherwise rare tumor, histiocytic sarcoma (HS). While recent studies have identified driver mutations in the MAPK pathway, identification of key predisposing genes has been elusive. Studies have identified several loci to be associated with predisposition to HS in BMDs, including near the <i>MTAP/CDKN2A</i> region, but no causative coding variant has been identified. Here we report the presence of a coding polymorphism in the gene encoding FANCG, near the <i>MTAP/CDKN2A</i> locus. This variant is in a conserved region of the protein and appears to be specific to BMDs. Canine fibroblasts derived from dogs homozygous for this variant are hypersensitive to cisplatin. We show this canine <i>FANCG</i> variant and a previously defined hypomorphic <i>FANCG</i> allele in humans impart similar defects in DNA repair. However, our data also indicate that this variant is neither necessary nor sufficient for the development of HS. Furthermore, BMDs homozygous for this <i>FANCG</i> allele display none of the characteristic phenotypes associated with Fanconi anemia (FA) such as anemia, short stature, infertility, or an earlier age of onset for HS. This is similar to findings in FA deficient mice, which do not develop overt FA without secondary genetic mutations that exacerbate the FA deficit. In sum, our data suggest that dogs with deficits in the FA pathway are, like mice, innately resistant to the development of FA.