Testing of dogs: Dwarfism

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Dwarfism in dogs

Pituitary dwarfism, also called nanism, is a metabolic disorder that affects German shepherds, Saarloos Wolfdogs and Czechoslovakian Wolfdogs. The disease is characterised by degeneration of hypophysis/pituitary resulting in deficiency of pituitary hormones, in particular in reduced level of growth hormone, thyrotropin, prolactin and gonadotropins and on contrary the secretion of adrenocorticotropic hormone remains normal.

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Genetics of Dwarfism

The dwarfism is caused by mutation of LHX3-gene on CFA9 chromosome coding for transcription factor that precludes effective expansion of a pituitary stem cell after the differentiation of the corticotrope cells.  The sequencing of LHX3-gene revealed the deletion c.622-37-31del of one of six 7bp repeats in intron 5 of LHX3-gene that causes reduction of the intron size to 68 bp.  In one German shepherd, the heterozygosity for an insertion of an ACA trinucleotide sequence in exon 5 has been proven.

Genomia performs test to detect both above described gene mutations leading to dwarfism.

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Heredity

Mutation, that causes Dwarfims, is inherited as autosomal recessive. The disease develops in individuals, who inherit the mutated gene from both parents. These individuals are designated as P/P (positive / positive). Molecular genetic tests can be used to confirm the diagnosis. The carriers of the mutated gene (N/P, i.e. negative/positive) are clinically healthy, but pass the gene on to their offsprings. If two heterozygous dogs (N/P) are mated, theoretically there will be 25 % healthy offsprings (N/N), 50 % offsprings will be the carriers and 25 % offsprings inherit the mutated gene from both parents and will suffer from the intestinal malabsorption (P/P).

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Clinical signs of dwarfism

The affected dogs can have normal size during the first weeks of their lives. Then, they grow slower than their brothers and sisters in the litter what is also obvious from the different gains in weight. Between the 3rd and the 4th month of age the differences are already evident. The affected dogs are the smallest puppies in the litter with obviously slowed-down growth and they never reach full size in adulthood. Other distinct sign is that the dogs always have "puppy coat" with signs of alopecia on the body and the neck. The affected dogs lose their hair so that their skin becomes irritated and hyperpigmented and therefore they have a darker skin. Moreover, the skin is much more subject to bacterial dermal infections due to decreased skin immunity.

The pituitary insufficiency is a severe disorder having impact on other body organs. For example, the deficiency of the growth hormone leads to insufficient kidney development causing chronic kidney failure. The lack of TSH often results in decreased function of thyroid gland which causes that the animals are slowed down and apathetic.  In male dogs the deficiency of gonadotropins may cause cryptorchidism. The female dogs are in rut without ovulation.

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Treatment

The treatment is rather based on the compensation of accompanying health problems.

A treatment with canine growth hormone would be the most logical variant.  Unfortunately, it is not possible, as the canine growth hormone is not available for use as a therapy.  Therefore, a possible solution would be the use of human growth hormone. In past, experiments with the treatment of hypophysis in dogs by human growth hormone were described. This treatment is not only very expensive, but also the production of antibodies against the human growth hormone hinders its use for treatment.  The use of porcine growth hormone seems to be a more suitable alternative. The administration of the porcine growth hormone will not cause production of antibodies as the amino acid sequence of the porcine growth hormone is identical with the canine one. But even this solution has its difficulties. This treatment can result in development of Diabetes mellitus due to the increased level of growth hormone. Therefore it is recommended monitoring of plasma levels of growth hormone and glucose during the treatment.

As an alternative, a long-term treatment with medroxyprogesterone acetate or proligestone is possible. The progestins are able to induce expression of the gene for growth hormone in the mammary gland of dogs. However, this treatment also brings further complications in form of repeating periods of itching pyodermia and cystic endometrial hyperplasia in female dogs.

The recommended therapy for treatment of the secondary hypothyroidism is the administration of synthetic levothyroxine. As its absorption and metabolism are variable, the dose of levothyroxine must be adapted to achieve satisfactory therapeutic response and therefore the patients should be carefully followed up.

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Prognosis

The prognosis is poor without the right treatment. At the age of 3-5 years, the dog is bare, thin and apathetic and lethargic. Fortunately, the prognosis improves significantly when the puppies affected with dwarfism are treated properly and in time with levothyroxine and either porcine growth hormone or progestins.

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References:

Annemarie M.W.Y. Voorbij; Hans S. Kooistra, DVM, PhD, Dipl ECVIM-CA ; Pituitary Dwarfism in German Shepherd Dogs ; JVCS, Vol. 2, No. 1, January 2009

Annemarie Voorbij and Hans Kooistra et al. ; Pituitary dwarfism in German shepherd dogs and Saarloos wolfhounds ;  Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University

Kate L. Tsai, Rooksana E. Noorai et al. ; Genome-wide association studies for multiple diseases of the German Shepherd Dog ; Mamm Genome (2012) 23:203-211 ; DOI 10.1007/s00335-011-9376-9

Annemarie M. W. Y. Voorbij et al; A Contracted DNA Repeat in LHX3 Intron 5 Is Associated with Aberrant Splicing and Pituitary Dwarfism in German Shepherd Dogs ; PLoS ONE 6(11): e27940. doi:10.1371/journal.pone.0027940

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Usual turnaround time: 7 business days
1 test price: 54.00 $ without VAT