What is Cystinuria?
Cystinuria is a genetic defect. The defect affects the kidney tubules. This in turn affects the kidney’s ability to filter cystine (an amino acid). The filerting process prevents this amino acid from going the urine. When this filtering action fails cystine passes into the urine. Over time crystals and/or stones can form. These stones can enter the urethra and cause an obstruction preventing the flow of urine. This form of blockage is more common in males due to their anatomy. Once there is a blockage the bladder is unable to empty. The bladder is likely to rupture which can be fatal.
Cystinuria is congenital in dogs where the issue is more common. Cystinuria is more common in Newfoundlands, Labradors and Scottish Deerhounds. However, it can take many years for the crystals/stones to form in order that symptoms present themselves. Sometimes symptoms do not present themselves.
Unlike other bladder stones, cystine stones will generally dissolve or breakdown with treatment. There are some drugs that can be given to try and break down the stones. These drugs are risky and are expensive. Drugs are not typically advised unless there are no other options. Generlly, the stones are removed surgically.
In Basenjis the symptoms may present at 17 months-11 years old. Cystinuria has been known in Basenjis for a long time. It is mentioned in the Complete Basenji by Elspet Ford. Although cases are rare this issue seems to be on the increase.
Mode of Inheritance
The mode of inheritance in Newfoundlands and Labradors is autosomal recessive. However, there is evidence pointing to the mode of inheritance being autosomal recessive with incomplete penetrance. That is a trigger is thought to be required for dogs predisposing of cystinuria to develop stones. The mode of inheritance in other breeds, although thought to be autosomal recessive, is not confirmed. The University of Pennsylvania are researching this issue in dogs and cats.
- obvious pain when attempting to urinate;
- poor urine flow;
- blood in the urine;
- a fowl rotten egg smell to the urine due to the presence of cystine crystals;
- dogs become despondent;
- walk with back arched due to pain in the kidney location; and/or
- cannot pass urine due to a blockage (this needs immediate veterinary treatment)
In cases where a dog is diagnosed with this condition but is not presenting:
- crystals and/or stones;
- problems urinating; and/or
- signs of pain or discomfort;
a special diet may be advised. This diet is usually very low in protein which can help reduce the risk of stones forming. Some supplements can also administered to reduce the risk of stones forming. In the case where stones have formed usually the only course is to have them surgically removed. Removal will prevent possible blockages in the urinary tract. When a blockage has occurred a process called hydropulsion is employed. This process pushes the stone back into the bladder. Once the stone is in the bladder it can be removed.
Once diagnoses the prognosis is generally good. A change of diet is generally recommended. Further testing might be required to ensure that stones do not form. Once removed stones can re-form so continued observation is required.