Dog breeds with dwarfism, a genetic mutation that impacts their health and well-being.

At first glance, a dachshund or a basset hound may simply appear to be elongated, adorable versions of other breeds. However, their short-legged, long-bodied appearance isn't just a matter of aesthetics or deliberate selection by breeders. It's the result of a specific genetic mutation that produces a type of dwarfism called achondroplasia or chondrodysplasia . Although we perceive them today as adorable-looking pets , the origin of this characteristic has functional roots and profound consequences for their health and well-being.

Dogs with dwarfism vs. small dogs

It's crucial not to confuse dwarf breeds with simply small ones. A Chihuahua or a Maltese are toy -sized dogs, but proportionate, meaning their body, legs, and skull are similarly harmonious to their larger counterparts . In contrast, dogs with dwarfism exhibit very specific physical disproportions, with shortened limbs, large skulls, and sometimes curved legs due to abnormalities in bone development.

These differences are not merely morphological issues, but have clinical implications. While small dogs do not usually have problems derived from their size , those with dwarfism may suffer musculoskeletal, respiratory and joint disorders throughout their lives.

The genetic origin of dwarfism

A study published in Science in 2009 by the team led by Heidi Parker identified the origin of dwarfism in dogs. It involves an extra copy of the FGF4 gene, abnormally inserted into the canine genome, which regulates bone growth during fetal development. In affected dogs, this "errant" version of FGF4 acts disproportionately, inhibiting proper cartilage ossification in the limbs.

The surprising thing is that this mutation, known as a retrogene, occurred only once in the evolutionary history of the domestic dog , yet is present today in at least 19 different breeds. These include the dachshund, the Cardigan and Pembroke Welsh corgi, the Pekingese, the Dandie Dinmont terrier, the basset hound, and the English bulldog, among many others. The mutation, although completely natural, became established in the canine population through artificial selection, as it was useful for functions such as hunting in burrows or herding at ground level.

There is also a hormonal dwarfism, pituitary dwarfism , which is much rarer and not sought after by breeders. This condition occurs when the body doesn't produce enough growth hormone, and the dog fails to develop normally. It occurs with some frequency in the German Shepherd and all derived breeds. Dogs affected by pituitary dwarfism are much smaller than expected, have sparse fur, infertility, and other endocrine complications. All canine organizations around the world maintain the prohibition that these dogs should not be used for breeding.

Health consequences

Selecting dogs with such extreme characteristics has a cost, and dwarfism carries a predisposition to suffer from:

Furthermore, dogs with dwarfism often have a shorter life expectancy and may require surgical interventions or physical rehabilitation throughout their lives, so it is important to maintain frequent veterinary checkups and a healthy weight to preserve their quality of life.

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