This is an inherited glycogen storage disease. It is caused by a coding mutation, which leads to a lack of phosphofructokinase enzyme or inactivity.

Without the PFK enzyme muscle cells and red blood cells are not able to produce enough energy for their needs.

Affected dogs display the following intermittent, clinical signs: weakness, lethargy, exercise intolerance, poor performance, muscle cramps, anaemia, jaundice and dark-coloured urine. Dark-coloured urine, a hallmark of this disorder, usually appears after strenuous exercise or after excessive barking, panting or heat exposure and is caused by the destruction of the red blood cells .