Congenital hypothyroidism in domestic shorthaired cats

Hypothyroidism is a lack of thyroid gland activity. Since thyroid hormones are crucial for bone development, the most common clinical sign in cats is disproportionate dwarfism. It is characterized by a large skull with shortened jaw and ears, a square torso and short limbs, often combined with spinal deformity and delayed tooth growth. The typical feature is a goitre, an enlarged thyroid gland. Hypothyroidism is also characterized by mental deficiency and abnormalities of the nervous system. Other less specific features include hypothermia, anorexia, obesity, constipation or lethargy.

In the short-haired domestic cat, a causal missense mutation c.1333G>A of the TPO gene, encoding the enzyme thyroid peroxidase, which is involved in the synthesis of thyroid hormones, has been identified.

The mode of inheritance of the mutation is autosomal recessive. This means that only individuals who inherit the mutated gene from both parents will develop the disease. Carriers of the mutated gene are clinically healthy but pass the mutation on to their offspring. In the case of a mating between two heterozygous individuals, theoretically 25% of the offspring will be completely healthy, 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 the disease.

The genetic test can clearly reveal the genotype of the animal and is a useful tool for breeders to prevent unintentional breeding of affected kittens.

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References:

Giger, U., Raj, K., Murrow, C.V., Traas, A., Erat, A.M., van Hoeven, M., Mazrier, H., Haskins, M.E. : Congenital hypothyroidism with goiter in cats due to a TPO mutation. J Vet Intern Med 29:448; Abstract ESVE-O-4, 2015