Primary hyperparathyroidism (PHPT)

Primary hyperparathyroidism (PHPT) is an inherited condition that leads to a disruption of the regulation of calcium levels in the body. Normally, the parathyroid hormone (PTH) is released when the calcium level in the blood is too low. It causes calcium to be released from the bones, reduces the amount of calcium excreted by the kidneys, and lowers the phosphate level. In affected dogs, however, parathyroid hormone is produced in an uncontrolled way. As a result, the calcium level in the blood remains permanently elevated (hypercalcaemia), while at the same time calcium is lost from the bones. Possible consequences include progressive weakening of the bones, kidney problems up to kidney failure, as well as other metabolic disorders.

In the Keeshond dog (German Spitz), a genetic variant in the SIRT6 gene (Sirtuin-6) has been identified that is associated with this condition. This variant changes the structure of an important protein and impairs its function. The variant is inherited in an autosomal dominant manner, meaning that just one altered copy of the gene is sufficient for a dog to develop the disease. Both dogs with one altered gene copy (N/PHPT) and dogs with two altered gene copies (PHPT/PHPT) may develop symptoms.

The condition typically appears later in life, usually after the age of 8 years. Many affected dogs show no obvious symptoms even up to the age of 9–10 years. Genetic testing allows early identification of affected animals and supports appropriate breeding decisions.

In addition, another variant in the promoter region of the EEF2 gene (eukaryotic elongation factor 2) has been described, which may influence the activity of the gene. This variant has been used for genetic testing in the USA since 2008. However, whether it is reliably associated with the condition outside the Keeshond (Spitz) breed or outside the US population is currently not clearly established.