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Congenital and Inherited Disorders of the Digestive System of Dogs

By Dana G. Allen, DVM, MSc, DACVIM, Professor and Chair, Department of Clinical Studies, Ontario Veterinary College, University of Guelph ; Lisa E. Moore, DVM, DACVIM ; Carlton L. Gyles, DVM, PhD, Professor Emeritus, Department of Pathobiology, Ontario Veterinary College, University of Guelph ; Sharon Patton, MS, PhD, Professor of Parasitology, Department of Biomedical and Diagnostic Sciences, College of Veterinary Medicine, University of Tennessee ; Andrew S. Peregrine, BVMS, PhD, DVM, DEVPC, DACVM, Associate Professor, Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada ; Thomas W. Swerczek, DVM, PhD, Professor, Department of Veterinary Science, University of Kentucky ; Ben H. Colmery, DVM, DAVDC ; James G. Fox, DVM, MS, DACLAM, Professor and Director, Division of Comparative Medicine, Massachusetts Institute of Technology ; H. Carolien Rutgers, DVM, MS, DACVIM, DECVIM-CA, DSAM, MRCVS, Senior Lecturer, The Royal Veterinary College, University of London ; Jörg M. Steiner, DrMedVet, PhD, DACVIM, DECVIM-CA, AGAF, Associate Professor and Director, Gastrointestinal Laboratory, Department of Small Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A & M University ; Sofie Muylle, DVM, PhD, Faculty of Veterinary Medicine, Department of Morphology, Ghent University ; Walter Ingwersen, DVM, DVSc, DACVIM, Specialist, Companion Animals, Boehringer Ingelheim (Canada) Ltd, Vetmedica ; Stanley I. Rubin, DVM, MS, DACVIM, Clinical Professor, Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois at Urbana-Champaign ; Sharon Campbell, DVM, MS, DACVIM, Manager, Pharmacovigilance Regulatory Affairs, Veterinary Medicine Research and Development, Pfizer Inc.

Also see professional content regarding congenital and inherited disorders of the disgestive system.

Congenital abnormalities are conditions that an animal is born with; they are often called “birth defects.” Some of these conditions are inherited and tend to occur within particular families or breeds, while others are caused by chemicals or injury during pregnancy. For still others, the cause is unknown. Some of the most common congenital abnormalities of the digestive tract in dogs are described below.

Mouth

A cleft palate or cleft lip (harelip) is caused by a defect in the formation of the jaw and face during embryonic development. It leads to a gap or cleft in the center of the lip, the roof of the mouth (hard palate), or both. Often this condition leaves an open space through the roof of the mouth into the breathing passages. These conditions have a wide range in severity. Usually the upper lip and palate are affected; a cleft in the lower lip is rare.

Certain breeds are more prone to cleft palate than others. The defect is more common in Beagles, Cocker Spaniels, Dachshunds, German Shepherds, Labrador Retrievers, Schnauzers, and Shetland Sheepdogs. Dog breeds with short heads (brachycephalic breeds) can have up to a 30% risk of the disorder. Most cases are inherited, although nutritional deficiencies during pregnancy, drug or chemical exposure, injury to the fetus, and some viral infections during pregnancy have also been suggested as causes.

Cleft palate or lip will usually be noticed shortly after birth when the puppy might have problems nursing. For example, milk might be seen dripping from the nostrils or the puppy might have difficulty suckling and swallowing. The veterinarian can readily identify the problem by examining the puppy’s mouth. Affected puppies require intensive nursing care, including hand or tube feeding and possibly antibiotics to treat respiratory infections. Surgical correction is effective only in minor cases, and is usually done when puppies are 6 to 8 weeks old to minimize further complications. A variety of surgical techniques are used, and the success rate in dogs is improving. The decision to perform surgery should be made carefully, and the affected animal should be spayed or neutered to prevent passing the defect on to its offspring.

Brachygnathia occurs when the lower jaw is shorter than the upper jaw. It can be a minor problem or a serious defect depending on the degree of abnormality. Mild cases may cause no problems. More severe cases can cause damage to the hard palate (roof of the mouth) or restriction of normal jaw growth. The lower canine teeth are often removed or shortened to prevent this damage.

Prognathia occurs when the lower jaw is longer than the upper jaw. This characteristic is normal in some breeds (for example, Boxers, Bulldogs, Pugs, and other breeds with shortened heads) and does not usually require treatment.

Ankyloglossia or microglossia refers to incomplete or abnormal development of the tongue. The condition in dogs is often referred to as “bird tongue.” Affected puppies have difficulty nursing and do not grow properly. Examination of the mouth reveals missing or underdeveloped portions of the tongue. This condition is generally fatal.

Some Chinese Shar-Peis have a condition called tight-lip syndrome in which the lower lip covers the lower front teeth and folds over the teeth toward the tongue. Contact between the upper front teeth and the lower lip worsens the lip position and may cause the lower front teeth to shift. This condition can be corrected by surgery.

Common congenital defects in dogs include brachygnathia (shortened lower jaw) and prognathia (elongated lower jaw).

Teeth

In most animals, having too few teeth is rare, although in dogs, molars and premolars may fail to develop or erupt. In dogs, extra teeth are seen most often in the upper jaw. Although rare, sometimes a single tooth bud will split to form 2 teeth. The result may be crowding and rotation of the teeth; this condition requires tooth extraction to prevent or correct abnormalities of the bite that can lead to further dental problems.

Delayed loss of deciduous (“baby”) teeth in dogs is common. The teeth that do not fall out get in the way of the permanent teeth that are starting to erupt beneath them, altering the position of the permanent teeth within as little as 2 to 3 weeks. This results in bite problems or entrapment of food, leading to tooth and gum disease. For these reasons, retained deciduous teeth should be removed by your veterinarian as soon as possible.

Abnormalities in placement or shape of teeth are reported in various breeds of dogs. The effect on an animal’s health is variable and based on severity. In certain dog breeds with short, flattened heads (brachycephalic breeds), the upper third premolar and occasionally other teeth may rotate. Usually, this does not cause any problems, but it may require extraction of some teeth if crowding or bite abnormalities occur.

Abnormal development of tooth enamel (the hard outer surface of the tooth) can be caused by fever, trauma, malnutrition, poisoning, or infections such as distemper virus. The damage to the enamel depends on the severity and duration of the cause and can range from pitting to the absence of enamel with incomplete tooth development. Affected teeth are prone to plaque and tartar accumulation, which lead to tooth decay. Resin restoration is sometimes used to cover defects, although careful dental hygiene and home care is critical in reducing the incidence of complications. Discoloration of the enamel may also occur. Giving tetracycline antibiotics to pregnant females or to puppies less than 6 months old may result in permanent brownish-yellow stains on the teeth.

Cysts of the Head and Neck

Cysts (lumps) in the head and neck can be caused by defects during fetal development. These need to be distinguished by your veterinarian from abscesses or lumps caused by infection or other disease. These cysts tend to occur in specific locations and may have a characteristic feel to them, which can help the veterinarian to diagnose their cause.

Esophagus

The muscular tube that leads from the back of the mouth to the stomach is known as the esophagus. Some congenital abnormalities of the esophagus seen in dogs include megaesophagus, vascular ring anomalies, and crichopharyngeal achalasia (see Table: Congenital Esophageal Disorders of Dogs). Signs of defects in the esophagus generally include regurgitation and problems with swallowing. These signs are especially noticeable when your dog starts to eat solid food. Surgical correction of some esophageal abnormalities (for example, vascular ring anomalies, in which abnormal blood vessels surround and restrict the esophagus) is effective if done early. If not, the esophagus can become permanently damaged by the stretching caused by trapped food.

Small pouches in the lining of the esophagus, called esophageal diverticula, will sometimes form. Signs depend on severity and are seen in only 10 to 15% of cases. When they do occur, they may cause accumulation of food or become inflamed. In rare cases they rupture. Treatment (if necessary) is by surgical removal of the pouch. This disorder may be more common in English Bulldogs.

Congenital Esophageal Disorders of Dogs

Type

Cause

Breeds Most Often Affected

Congenital megaesophagus

Abnormal nerve development in esophagus; sometimes part of more widespread nerve problems

Chinese Shar-Peis, Fox Terriers, German Shepherds, Great Danes, Irish Setters, Labrador Retrievers, Miniature Schnauzers, Newfoundlands; often part of laryngeal paralysis-polyneuropathy complex in Dalmatians

Vascular ring entrapment

Physical constriction of the esophagus by other tissues

Boston Terriers, German Shepherds, Irish Setters

Cricopharyngeal achalasia

Failure of the cricopharyngeal muscle (in the throat) to relax during swallowing

Toy breeds

Hernias

A hernia is the protrusion of a portion of an organ or tissue through an abnormal opening. One common congenital type involves an abnormal opening in the wall of the diaphragm (the sheet of muscle that separates the chest from the abdomen) or abdomen. The defect may allow abdominal organs to pass into the chest or bulge beneath the skin. Hernias may be congenital (present at birth) or result from injury. Signs of a hernia vary from none to severe and depend on the amount of herniated tissue and its effect on the organ involved. Hiatal hernias involve extension of part of the stomach through the diaphragm. These hernias may be “sliding” and result in signs (such as loss of appetite, drooling, or vomiting) that come and go. Hernias are diagnosed using x-rays; contrast studies (x-rays that include special dyes to outline organs) are often needed. Endoscopy may be used to diagnose sliding hiatal hernias. In many cases, correction of a hernia involv-ing the diaphragm requires surgery. However, the use of antacid preparations and dietary modification may control signs of a hiatal hernia, if they are mild.

Types of Hernias

General Area

Specific Type

Description

Diaphragm

Peritoneopericardial

Abdominal contents extend into the sac surrounding the heart

Pleuroperitoneal

Abdominal contents extend into the sac surrounding the lungs

Hiatal

Stomach and/or lower esophagus protrude through the esophageal opening (hiatus) into the chest cavity

Abdomen

Umbilical

Abdominal contents protrude at the site of the navel; most often genetic but sometimes caused by strain on the umbilical cord during or after birth

Inguinal

Abdominal contents protrude into the groin, above the scrotum of male animals

Scrotal

Abdominal contents protrude into the scrotum (the sac surrounding the testes) of male animals

Hernias involving the abdominal wall are called umbilical, inguinal, or scrotal, depending on their location (see Table: Types of Hernias). Diagnosis of umbilical hernias is usually simple, especially if the veterinarian is able to push the hernia back through the abdominal wall (called “reducing the hernia”). These hernias are corrected by surgery. Small hernias are often corrected at the same time that the dog is spayed or neutered. The tendency to develop hernias may be inherited.

Stomach

Besides hiatal hernia (see Congenital and Inherited Disorders of the Digestive System of Dogs : Hernias), another common abnormality involving the stomach is pyloric stenosis. It is likely that pyloric stenosis is inherited. This condition results from muscular thickening of the pyloric sphincter (the “exit” of the stomach). The thickening of this opening slows or blocks the flow of digested food from the stomach to the small intestine. Affected breeds include smaller breeds and those with flattened, shortened heads, especially Boxers and Boston Terriers. Because the flow of food out of the stomach is restricted, dogs with this condition will often vomit food for several hours after a meal. Treatment is through dietary modification and medication. In more severe cases, surgery may help.

Small and Large Intestine

Maldigestion is a condition in which certain foods are not properly digested. Malabsorption occurs when nutrients are not properly absorbed into the bloodstream. These conditions often cause persistent digestive system problems, including vomiting, weight loss, diarrhea, or a combination of these signs. There are many potential causes of maldigestion and malabsorption. Some are in-herited; some are acquired. Most are associated with inflammation of the intestines (called inflammatory bowel disease). Inherited conditions may occur more often in specific breeds. For example, Irish Setters have a family tendency for sensitivity to wheat protein (gluten), with signs beginning as early as 6 months of age. The wheat sensitivity is both confirmed and treated through the use of gluten-free diets. Malabsorption and maldigestion are often treated with a combination of dietary changes and medication; the exact treatment will depend on the condition being treated. In certain conditions in which protein loss is severe (for example, in Soft-coated Wheaten Terriers with protein-losing enteropathy and nephropathy), neither dietary changes nor treatment have been proven effective, and the outlook is poor.

Various malformations of the intestines can occur as birth defects, including duplication of sections of the intestine or rectum, failure of the rectum to connect with the anus, and openings between the rectum and other structures such as the urethra or vagina. Surgical correction is usually needed. The success rate depends on the extent of the malformation.

Liver

The most common liver defect present at birth is portosystemic shunt. In a healthy animal, blood coming from the intestines is processed by the liver, which removes toxins from the bloodstream before they reach the brain or other organs. In an animal with a portosystemic shunt, however, blood bypasses the liver through one or more “shortcuts” (shunts) and enters directly into the general circulatory system. Breeds with an increased risk of this defect include Yorkshire Terriers, Miniature Schnauzers, Cairn Terriers, Maltese, Scottish Terriers, Pugs, Irish Wolfhounds, Golden Retrievers, Labrador Retrievers, German Shepherds, and Poodles. Signs of a portosystemic shunt include nervous system disturbances and a failure to grow and thrive. In the late stages, protein-containing fluid may accumulate in the abdomen, a condition called ascites. Your veterinarian may also notice enlargement of the kidneys and kidney stones. A definite diagnosis is made by using an opaque dye to highlight the blood vessels, followed by x-rays. This procedure can identify the location of the shunt and determine whether it is single or multiple. It also allows the veterinarian to assess whether surgical correction is possible. Animals with multiple shunts tend to do poorly.

Hepatoportal microvascular dysplasia is another disorder that results in blood entering the circulatory system without being detoxified by the liver. In this disease, the shunting occurs within the liver itself. The syndrome occurs with some frequency in Cairn and Yorkshire Terriers and has also been reported in Maltese, Dachshunds, Toy and Miniature Poodles, Bichon Frise, Pekingese, Shih Tzus, and Lhasa Apsos. It generally causes no signs. Dogs that do exhibit signs may be treated with medication. Surgery is not an option because the shunting is caused by many small blood vessels, not a single prominent one that can easily be corrected.

Copper-associated hepatopathy is a defect that causes copper accumulation in the liver. This results in development of chronic hepatitis and cirrhosis of the liver. The condition is found in Bedlington Terriers. An acute form of the disease in seen in young (less than 6-year-old) dogs, and chronic liver failure is seen in older dogs. Carrier dogs, which have no signs of the disease, are also seen. Elevated copper levels have also been observed as part of the inherited liver disease of West Highland White Terriers, Skye Terriers, and Doberman Pinschers. There are apparent variations even within breeds; for example, liver copper levels are worse in Bedlington and West Highland White Terriers of North American descent than in the same breeds from Europe or other regions. Treatment involves the use of drugs that bind copper (chelators), low-copper diets, and other supportive measures directed at helping animals with liver disease. If your dog has copper-associated hepatopathy, follow your veterinarian’s directions for medication, diet, and other treatment carefully and fully.

Other liver developmental anomalies include hepatic (liver) cysts, which generally cause no signs of illness. They are of significance mainly because they must be differentiated from abscesses in the liver. A veterinarian who finds a hepatic cyst will often want to examine the kidneys, because hepatic cysts often occur along with polycystic kidney disease.

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Also see professional content regarding congenital and inherited disorders of the disgestive system.

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