EIC appears to be a genetically simple trait that is due to a mutation in just one of the approximately 24,000 genes present in a dog’s genome. We have designated the letter E to indicate the mutant form of the EIC gene and N to indicate the normal form of this gene. Every dog has two copies of this gene, one inherited from the dam and one inherited from the sire. Every dog inherits either the N or the E form of the EIC gene from each parent.
A dog’s particular combination of E or N forms of the EIC gene is known as its genotype. The genotype of a normal dog that is clear of the EIC mutation is designated as N/N. Our data thus far shows that dogs with the E/N genotype do not typically show either strong or consistent signs of EIC. E/N dogs are referred to as carriers or heterozygotes. More than 95% of dogs that have the classical signs of EIC, and have had multiple well-documented collapse episodes, have the E/E genotype. Such dogs may be referred to as homozygotes for the EIC mutation.
All parents of dogs with EIC that we have tested so far are either E/N or E/E. This means that the parents are either unaffected carriers of the mutant EIC gene, or they are homozygous for the mutant EIC gene and therefore genetically susceptible to EIC themselves.
The genetic term that best describes the research data gathered to date is that EIC is inherited in an autosomal recessive fashion, because two copies of the mutant form of the EIC gene (i.e., the E/E genotype) are usually required for a dog to be affected, and an affected dog gets an E form of the EIC gene from each parent.