English Cocker Spaniel Texas
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.