Dilated Cardiomyopathy Research
It seems surprising that in January we will have been screening Great Danes as part of the DCM research for 4 years. In that time I have got married, changed my name, started to understand the ins and outs of showing dogs, and finally achieved my Diploma in cardiology!
Also, we have scanned over 140 individual Danes, and gained a valuable insight in to the cardiac problems these wonderful dogs suffer from. As most people are aware, this research started as part of the LUPA project, investigating the genetic basis of a variety of diseases in dogs, including DCM. With your help, we have collected DNA samples from Great Danes with and without DCM, and we have submitted these for genetic analysis. As with many things in life, this has proven to more complicated than we originally thought, and so far we have not identified a single genetic marker for DCM in Danes – there appears to many. Thanks to our ongoing research, we continue to provide DNA samples from dogs in the UK, so that more information can be gained. Hopefully, we will soon be able to identify genetic markers, and possible the genes involved in DCM in Danes.
The reason that the search for a gene is so important is that it allows us to detect at-risk dogs from birth. At the moment, our only way of identifying DCM prior to death is to do a heart scan. From my previous articles, readers will be aware that these abnormalities on heart scan so not become apparent until later in life (some Danes do not develop DCM until they are much older) and therefore a normal scan in a dog prior to breeding for the first time can be completely normal.
We have achieved a number of things in the last 4 years. We have scanned a large number of dogs, and identified that there is a high prevalence of DCM in this breed. So far, about 18% of the dogs screened have been definitively diagnosed with DCM. A further 11% are considered very likely to develop DCM in the future, based on the heart scan. This would make the prevalence of the disease about 29% (1 in 3 Danes have DCM). A less stringent way of identifying dogs with DCM is to assign them points for various abnormalities on a heart scan. This has been suggested by a taskforce of cardiologists (Dukes-McEwan et al, Journal of Veterinary Cardiology 2003), and this taskforce suggests that dogs scoring 6 or more are likely to have DCM. If we use this scoring system for our dogs, a much higher number of dogs would be classified as affected, with a prevalence of up to 47%!
One of the most important aspects of the screening is that we have many dogs returning for follow-up scans. This allows us to follow all the dogs over time, and see if the dogs do go on to develop DCM when we think they will, and be certain that dogs that are normal initially, stay normal. It also means that we can determine the significance of any mild abnormalities that we see on the scans – some of these mild ‘abnormalities’ can in fact be completely normal. We have also found some previously unidentified congenital heart defects (abnormalities that have been present since birth) in a small number of the dogs that have come for screening. In these cases, a scan prior to breeding for the first time would have identified the abnormality – if only it was as easy for DCM!
We have recently published some new reference intervals for various heart scan measurements in Great Danes that can be accessed by cardiologists around the world. We have identified the following:
Bitches have smaller hearts than dogs. This is probably because of differences in bodyweight and size. It is important that cardiologists are aware of this, if they are scanning your dog to identify DCM, as what is considered normal for a dog may actually be abnormal in a bitch, thus changing the final result of the scan.
Mild reduction of pumping ability is normal in Danes. Again this means that some dogs that were given an ‘equivocal’ result in our screening are likely to be normal. This is important to know as it means your dog will not necessarily be considered abnormal when scanned.
Danes are very likely to have ventricular arrhythmias (palpitations) which we think can cause sudden death. We are continuing to research this by using Holter monitors (24 hour ECG).
Analysis of pedigrees from our dogs suggests that the disease is inherited as an autosomal dominant trait, which is different to previous research in Danes (previously suggested to be X-linked inheritance). This has important implications for breeding from affected dogs (all affected dogs have the potential to pass the disease on to their puppies, regardless of whether they are out-crossed with another normal dog).