Dwarfism (Isolated Growth Hormone Deficiency) in Chihuahuas

Chihuahua dwarfism, also known as isolated growth hormone (GH) deficiency, is a rare hereditary disease affecting skeletal development and overall growth of the dog. The disease is characterized by proportionate stunted growth, retained dental development, and retained puppy hair coat.

The cause of the disease in Chihuahuas is the c.573_578del mutation in the GH1 gene, which codes for growth hormone. The mutation leads to a deficiency of growth hormone, which prevents the dog from growing and developing normally.

The mutation is inherited in an autosomal recessive manner. This means that the disease only develops in individuals who inherit the mutated gene from both their parents. Carriers of the mutated gene are clinically healthy, but they pass the mutation on to their offspring. In the case of mating two heterozygous individuals, theoretically 25% of the offspring will be so-called pure (without the mutation), 50% of the offspring will be carriers, and 25% of the offspring will inherit the mutated gene from both parents and will therefore be affected by this disease.

A genetic test can clearly reveal the genotype of the animal and is a suitable tool for breeders to prevent the unintentional breeding of affected puppies.

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References:

Iio, A., Maeda, S., Yonezawa, T., Momoi, Y., Motegi, T. : Isolated growth hormone deficiency in a Chihuahua with a GH1 mutation. J Vet Diagn Invest 32:733-736, 2020. Pubmed reference: 32646299