Part of the official UK Kennel Club testing scheme in Spaniel (Cocker)
Familial Nephropathy (Cocker Type), is a hereditary kidney disorder that affects Cocker Spaniels and related breeds. This condition leads to the progressive and ultimately fatal deterioration of the kidneys. Dogs with FN typically develop chronic renal failure between the ages of 6 months and 2 years, resulting in the destruction of both kidneys.
The first signs of FN include increased water consumption, changes in growth rate or weight loss, reduced appetite, weakness, fatigue and vomiting. In affected dogs, there is a defect that allows protein from the blood to be filtered by the kidneys and excreted in the urine, leading to abnormal levels of protein in the urine, usually detectable between 4-6 months of age. Subsequently, symptoms of chronic kidney disease manifest a few months after the presence of excessive protein in the urine is observed. Sadly, affected dogs typically succumb to chronic kidney failure by the age of one to two years.
The single base substitution in the gene called COL4A4 that causes Familial Nephropathy in Cocker Spaniel dogs is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Familial nephropathy during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Familial nephropathy as a result of the COL4A4 mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Familial nephropathy should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the COL4A4 mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with Familial Nephropathy, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.