Boxer Breed Council

UK BOXER CARDIOMYOPATHY IN PERSPECTIVE

by
Bruce M Cattanach BSc PhD DSc FRS
Published in Boxer Showcase, Dog World, July 2008

An inherited form of the heart disease, cardiomyopathy, was first recognised in the UK Boxer only a few years ago. Some breeders have found its presence hard to accept. The following notes represent an attempt to place the problem in perspective and summarise the current situation identified by the Breed Council Health Committee.

Humans:

Heart disease is one of the most extensively researched diseases in humans, possibly second only to cancer.

Cardiomyopathy is one of the most prevalent human heart diseases.

There are many different causes of CM. Some may be due to viral or other external agents that cause heart damage, but many more have a genetic basis.

Age of onset of the inherited forms of CM are very variable.

Over 40 genes, mutations of which independently can cause CM, are known

The different CMs may show different modes of inheritance but one, known as ARVC (arrhythmogenic right ventricular cardiomyopathy), almost invariably shows a dominant mode of inheritance with low penetrance (the disease does not always occur when the gene is present).

Dogs:

Several different CMs are known in dogs. Some may again be viral-induced but others, appearing in breeds or families, have a genetic basis.

In Boxers, CM was first formerly described in America by cardiologist, Neil Harpster. He had been asked by the Hamilburgs to investigate the cause of deaths in their famous Salgrays kennels. His findings were published in a veterinary journal in 1983. Since, then all American Boxer breeders with interest in health issues have been aware of this CM.

In more recent years, American vet/geneticist Kate Meurs has investigated Boxer CM in depth and has recognised that this Boxer form of canine CM corresponds with the ARVC form in humans. She has further concluded that the inheritance is, as in humans, that of a dominant with low penetrance. Much recent effort has been put into finding the gene responsible. There is no question but that Boxer CM is inherited.

With this history and several importations of Boxers from America over the years it is hardly surprising that CM is now found in the UK. It would have been more surprising if the disease had NOT gained entry even though not all US imports would have carried the gene responsible.

UK cardiologists now recognise UK Boxer CM to be of the American ARVC type. This differs from the DCM (dilated cardiomyopathy) of Dobermans and other breeds, although the end effect can be the same. The term DCM has been used in the past to describe final stage Boxer CM.

UK Boxers:

The first recognition of Boxer CM in the UK derived from cardiologist Paul Wotton’s studies when he was working in Bristol about ten years ago. In a period of 18 months he amassed 26 cases of severe early onset CM of which 23 were related, suggesting a familial or genetic basis

Thereafter, the work of the first Breed Council Health Committee further highlighted and defined this family group showing that it spanned several kennel lines located in different parts of the country. A genetic, rather than an environmental basis, was therefore firmly indicated, consistent with the American work. Also suggested at that time was the existence of two other unrelated families with Boxer CM.

Since then, work by the current Health Committee has shown the first family identified has extended forward over the generations to involve numbers of kennels. It has also extended backwards such it seems likely that the gene came into the UK independently through two related American imports.

The second family appears to have a later onset CM that is harder to identify. It appears to have been with us for much longer and is more widespread. It appears to trace back to one or more earlier American imports.

The third line is extinct in the originally affected kennel, but may very well still be around elsewhere. It is also late onset. It is probably the oldest in origin.

Cardiologists have defined blood troponin, Holter and other veterinary tests to screen for and diagnose Boxer CM, and post-mortem facilities offering detailed histo-pathology are now also available.

Blood samples have been collected from over 30 dogs to help studies to find the gene for BCM. Half of these dogs are BCM cases and the rest relatives. There is an urgent need for samples from ‘control’ dogs, those that have no BCM risk whatever in their pedigrees.

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