An inherited disorder is one that is passed on starting with one age then on to the next. Such clutters seem all the more frequently in family hounds and might be breed speciﬁc. Some common examples are described below.
THE RISK OF DISEASE
Smaller gene pools and widespread inbreeding in the past have made pedigree dogs more likely than crossbreeds to be affected by inherited disorders. However, although crossbred dogs may be at reduced risk, they still have a chance of inheriting disease-causing genes from either parent.
HIP AND ELBOW DYSPLASIA
These two conditions occur mainly in medium-sized and large breeds. In dysplasia, structural defects either of the hip or the elbow cause a joint to become unstable, resulting in pain and lameness. Diagnosis is based on the dog’s history, together with joint manipulation and radiography.
Treatment may consist of pain relief, reducing exercise, and maintaining ideal body weight. Various surgical options are also available, including total hip replacement for hip dysplasia. After a set age (generally more than one year old), susceptible breeds can be screened for hip and elbow dysplasia.
A congenital defect, present from birth, aortic stenosis is a narrowing of the aortic valve in the heart. There may be no signs, the disorder being detected as a murmur when a vet listens to the heart with a stethoscope at a puppy check. It may be investigated further (with radiography, ultrasound, and ECG) or simply monitored, as only a few dogs can be treated surgically. Some dogs with aortic stenosis go on to develop congestive heart failure.
BLOOD CLOTTING DISORDERS
The most common inherited clotting disorder (in both dogs and humans) is hemophilia, in which lack of an essential factor for blood clotting results in recurrent bleeding. The faulty gene responsible is passed on by affected males to their female offspring, who remain unaffected themselves but can be carriers of the gene. Hemophilia can occur in both pedigree and crossbred dogs.
Another inherited blood clotting disorder is Von Willebrand’s disease, which affects many breeds of either sex. DNA tests are available for some breeds.
Dogs can be affected by several inherited eye conditions, including some that are easily visible, such as entropion (right), and others that need internal examination of the eye using specialized equipment. An eye disease that can occur in any breed and also in crossbred dogs is progressive retinal atrophy (PRA). In this disorder, there is degeneration of the retina—the layer of light-sensitive cells at the back of the eye—leading to loss of vision. An owner may become aware of PRA when a dog begins to display sight problems, which at ﬁrst may be only at night. PRA is diagnosed from examining the retina with an ophthalmoscope, and the vet may recommend more specialized investigations. There is no treatment and loss of vision is permanent. DNA screening is available for some breeds.
Various breeds of collie (Smooth and Border Collies, Shetland Sheepdog, and Australian Shepherd) and some other breeds are affected by a disorder known as collie eye anomaly (CEA), in which there are abnormalities in the choroid, a layer of tissue at the back of the eye. CEA can be detected from birth, so puppies are examined before they are three months old. The mildest form of CEA has little effect on sight, but the most severe form can cause blindness. DNA screening is available.
SCREENING FOR DISEASE
Routine screening is important in reducing the incidence of inherited diseases. For hip and elbow dysplasia, dogs are screened by having radiographs taken (see box opposite). In the past, eye conditions such as PRA and CEA could be identiﬁed only by examination, but the advent of DNA screening has improved the chances of detecting both these and many other inherited diseases.