Evaluation of the Apolipoprotein C-II Gene in Miniature Schnauzers with Idiopathic Hypertriglyceridemia
Miniature Schnauzers have a high prevalence of hypertriglyceridemia, reported to be 32.8% in 192 healthy Miniature Schnauzers in one study. While the actual cause of this condition has not yet been identified, this high prevalence of idiopathic hypertriglyceridemia in Miniature Schnauzers compared to other breeds suggests a possible hereditary etiology. Apolipoprotein C-II (apo C-II), a co-factor of lipoprotein lipase, plays a central role in triglyceride metabolism, and mutations of the gene encoding apo C-II have been associated with familial hypertriglyceridemia in humans. The aim of this study was to identify and compare the nucleotide sequence of the apo C-II gene of hypertriglyceridemic and non-hypertriglyceridemic Miniature Schnauzers, as well as non-hypertriglyceridemic dogs of other breeds, in order to identify polymorphisms that co-segregate with hypertriglyceridemia.
Blood samples were collected from 9 healthy Miniature Schnauzers with idiopathic hypertriglyceridemia, 6 healthy Miniature Schnauzers with a normal serum triglyceride concentration, and 2 dogs of other breeds with a normal serum triglyceride concentration. DNA was extracted from whole blood and the exonic and flanking intron sequences of the apo C-II gene were amplified. PCR amplicons were ligated into vectors and Escherichia coli organisms were transformed with ligation products. Recombinant organisms were grown and 4-6 colonies per sample were picked, transferred to broth, and grown for 24 hours. Plasmid DNA was extracted and sequenced and sequencing products were analyzed with an automated sequence analyzer. Obtained sequences were compared based on multiple sequence alignment and analyzed for co-segregation of polymorphisms with hypertriglyceridemia.
A total of 12 polymorphisms were initially identified in the apo C-II gene of Miniature Schnauzers. Each polymorphism was identified only in a single sequence from each dog, and none of the polymorphisms co-segregated with hypertriglyceridemia. PCRs were repeated for all dogs and exons where polymorphisms had been identified, and PCR amplicons were directly sequenced. None of the 12 initially identified polymorphisms were present in the sequences obtained after direct sequencing, suggesting that these polymorphisms were artifacts and did not represent single nucleotide polymorphisms.
In conclusion, based on the results of the present study, mutations of the apo C-II gene do not appear to be the cause of idiopathic hypertriglyceridemia in this group of Miniature Schnauzers.