Chondrodystrophy (CDDY with IVDD Risk) and Chondrodysplasia (CDPA)

Chondrodysplasia (CDPA) and chondrodystrophy (CDDY) in dogs are associated with retrogene insertions in the fibroblast growth factor 4 (FGF4) gene, which plays a key role in skeletal development. Two known FGF4 retrogenes contribute to short-limbed phenotypes: an insertion on chromosome 18 (FGF4L1) and an insertion on chromosome 12 (FGF4L2).

This test analyses both retrogene insertions:

FGF4L1 retrogene insertion on chromosome 18
FGF4L2 retrogene insertion on chromosome 12

The FGF4L1 insertion on chromosome 18 causes CDPA, an autosomal dominant mutation that alters signalling involved in bone and cartilage formation, leading to disproportionate dwarfism characterised by shortened limbs and a relatively long body.

The FGF4L2 insertion on chromosome 12 causes CDDY, a semi-dominant trait characterised by a short-legged phenotype. Dogs with two copies of the mutation are smaller than dogs with only one copy, which are already smaller than unaffected dogs. This same mutation can also lead to degeneration of the intervertebral discs, making affected dogs more susceptible to Hansen’s type I intervertebral disc disease (IVDD).

Dogs affected by CDPA exhibit disproportionately short limbs relative to their body size, often resulting in a characteristic “long and low” body shape. The severity of limb shortening can vary and may be accompanied by mild angular limb deformities such as outward turning of the front legs. Despite these changes in conformation, the overall body length and size are typically normal. CDPA primarily affects physical appearance and is generally not associated with severe health problems on its own, although it significantly influences skeletal structure and height.
In contrast, the mutation on chromosome 12 that causes CDDY can lead to degeneration of intervertebral discs (IVDD). These intervertebral discs act as cushions between the vertebrae in the spine, providing support and flexibility to the backbone. In cases of IVDD, the degeneration and eventual herniation of the discs will lead to compression of the spinal cord or nerves. Dogs with one copy of the CDDY mutation already have an increased risk of developing IVDD.