Mendelian trait/disorder: yes

Mode of inheritance: Autosomal

Considered a defect: yes

Key variant known: yes

Year key variant first reported: 2017

Cross-species summary: A form of disproportionate dwarfism, characterized by short limbs

Mapping: Brown et al. (2017) reported that a "genome-wide association analysis in a cohort of Nova Scotia duck tolling retrievers (NSDTRs) with and without severe SD identified a significant association on CFA12 due to a 12-Mb associated haplotype, of which 1.9 Mb was found to be shared in chondrodystrophoid breeds."

Molecular basis: Brown et al. (2017): an FGF4 retrogene insertion in chromosome CFA12 (12: g.33710178_33710179insMF040221.1; CanFam3) is "responsible for SD [skeletal dysplasia] in NSDTR [Nova Scotia Duck Tolling retrievers] . . . the insertion on CFA12 is 3,209 bp long (GenBank accession no. MF040221) and includes parental FGF4 cDNA (i.e., FGF4 exons spliced without introns) . . . . The insert also contains a majority of the predicted 5′-untranslated region (UTR), which includes the transcription start site (TSS) as only PCR primers FGF4_TSS.F1 and FGF4.R1 yielded a product in RT-PCR using cDNA from neonatal beagle IVD . . . . The insertion location is intergenic between the 3′-UTR of OGFRL1 ∼9.5 kb on the proximal side and ∼350 kb to the RIMS1 gene on the distal side." Because the retrogene is not included in NCBI's Gene database, the table below lists the normal FGF4 gene.

Clinical features: Brown et al. (2017): "Relative to the unaffected dog, the mildly SD-affected NSDTR has cranial bowing of the radius. Radiographic changes in the more severely SD-affected NSDTR include moderate cranial bowing of the radius, physeal widening, and incongruity of the elbow joint with the shape of the semilunar notch of the ulna being elongated."

Breed: Nova Scotia Duck Tolling retriever.