Genetic Cause of Autosomal Recessive Hereditary Nephropathy in the English Cocker Spaniel

Abstract

Background: Autosomal recessive hereditary nephropathy (ARHN) in the English Cocker Spaniel is caused by a type IV collagen defect, but the underlying mutation is unknown.Animals: One hundred thirty-four English Cocker Spaniels (12 with ARHN, 8 obligate carriers, and 114 others), 3 mixed breed dogs with X-linked hereditary nephropathy (XLHN), and 7 other dogs without hereditary nephropathy were included.Methods: Diagnosis of ARHN was based on transmission electron microscopy and immunostaining of kidney. Quantitative real time reverse transcriptase polymerase chain reaction (qRT-PCR) was used to compare COL4A3, COL4A4, and COL4A5 mRNA concentrations in the renal cortex from ARHN-affected English Cocker Spaniels, XLHN-affected dogs, and dogs without hereditary nephropathy. The entire coding region of COL4A4 was sequenced in 2 ARHN-affected dogs, 2 obligate carriers, 2 English Cocker Spaniels of unknown status, and 2 healthy mixed breed dogs. The exon containing the mutation was sequenced for all 134 English Cocker Spaniels.Results: Quantitative real time RT-PCR implicated COL4A4 as the gene harboring the mutation, and sequencing identified a single nucleotide substitution at base 115 as the cause of ARHN in English Cocker Spaniels. This mutation, which causes a premature stop codon in exon 3 of COL4A4, was segregated with clinical status in all affected dogs and obligate carriers. The mutation also was identified in 39 of 114 other English Cocker Spaniels with previously unknown status.Conclusions and Clinical Importance: The cause of this disease has been identified, and use of a test for the mutation will permit eradication of ARHN in the English Cocker Spaniel.

Progressive Juvenile Glomerulonephropathy in 16 Related French Mastiff (Bordeaux) Dogs

“…Urinalysis was performed either on samples collected by cystocentesis in 11 dogs (dogs 1-3, 5, 8, and [11][12][13][14][15][16] or on samples taken during natural voiding in 5 dogs (dogs 4, 6, 7, 9, and 10). Complete urinalysis (specific gravity, dipstick analysis, urinary protein/creatinine ratio, and bacterial culture) was performed in 8 dogs.…”

Kidney diseases caused by glomerular basement membrane typeIVcollagen defects in dogs

“…To date, 4 different examples of canine glomerular diseases caused by identified genetic type IV collagen defects have been recognized (Table ). Two are X‐linked and are caused by different COL4A5 mutations, and 2 are autosomal recessive and are caused by different COL4A4 mutations . However, all 4 mutations cause disruptions of gene translation leading to an inability to synthesize either complete α4(IV) or complete α5(IV) chains and thus preventing the assembly of the α3.α4.α5(IV) network that is crucial for maintenance of GBM structure and function in the adult kidney.…”

“…Although both parents of such a dog were obligate carriers of the condition, this entire scenario happened too infrequently and sporadically to permit breeders to confidently identify carriers well enough to eradicate the disease. Therefore, an autosomal recessive form of HN persisted in the English Cocker Spaniel breed world‐wide from the mid‐1940s until about 2007, when the causative mutation was identified and a genetic test for carriers became available . Since then, however, English Cocker Spaniel breeders have been able to reliably avoid mating carriers to one another, which has extinguished further production of HN‐affected English Cocker Spaniels in recent years.…”

“…Dogs with the autosomal recessive forms of HN that have been identified to date are homozygous for COL4A4 mutations that preclude synthesis of complete α4‐chains, so they also cannot form intracellular α3.α4.α5 heterotrimers or assemble a α3.α4.α5 network in their GBM. Although the onset and evolution of ultrastructural changes in their GBM has not been studied as thoroughly in these dogs as it has been in male dogs with XL‐HN, the events that are initiated by the absence of the α3.α4.α5 network are presumed to be similar in both genetic forms of the disease.…”

“…Importantly, despite the clinical and pathologic similarities that exist among them, each breed or kindred of dogs with genetically defined HN that has been identified to date has had a different (ie, unique to that breed/kindred) underlying causative mutation . The consequence of such breed‐specific mutations is the requirement for a different DNA‐based genetic test to identify the mutant allele in each separate dog breed or kindred that is affected.…”