Imerslund-Gräsbeck Syndrome Case Studies

WHAT IS YOUR DIAGNOSIS? A nine month old, male entire, Border Collie was presented as an emergency following acute collapse after a period of diarrhoea and lethargy. The dog had a history of poor growth, although was reported to be of a normal size at the times of his first and second vaccinations. Intermittent diarrhoea had been reported, with faeces ranging from water consistency to dry and crumbling. More recently he had become polyphagic, with what was described as a ravenous appetite. On examination, he was stuporous but responsive although recumbent. Mucous membranes were pale, and tacky. There was a bilaterally symmetrical ulceration affecting the dorsal surface of the tongue (fig. 1). He had a heart rate of 140 beats per minute, with synchronous, weak peripheral pulses and a respiratory rate of 30 breaths/minute with no evidence of adventitious lung sounds. There was no skin tent present. Abdominal palpation was unremarkable and he had a rectal temperature of 37.3oC. He was thin, with a body condition score of 2 out of 9, weighing 8.7 kg. A systolic blood pressure, obtained using the Doppler method, was 80 mmHg. The clinical parameters improved following several crystalloid boluses, although the patient remained subdued. Figure 1 : Image of tongue on initial presentation page 1 of 7 Haematology and biochemistry obtained at the time were as follows: Parameter Haematology White blood cells Neutrophils (seg) Neutrophils (band) Lymphocytes Monocytes Eosinophils Basophils RBCC PCV Hb MCV MCHC Platelets Biochemistry Albumin ALT AP Bile Acids Bilirubin (total) Calcium (total) Chloride Cholesterol CK Creatinine Globulin Inorganic Phosphate Potassium Protein (total) Sodium Triglycerides Urea Glucose Result Range Unit 1.7 1.411 0.00 0.20 0.456 0 0 2.26 0.149 5.0 65.8 33.9 113 6.0 – 15.0 3.6 – 12.0 0.0 – 0.0 0.7 – 4.8 0 - 1.5 0 – 1.0 0–0 5.5 – 8.5 0.39 – 0.55 12 – 18 60 – 77 32 – 36 200 – 500 x 109/l x 109/l x 109/l x 109/l x 109/l x 109/l x 109/l x 1012/l l/l g/dl Fl % x 109/l 25.4 30 109 5.2 0.1 2.2 106 4.9 143 59 20.2 1.65 4.3 45.6 142 0.55 2.8 5.0 26 – 35 21 – 102 20 – 60 0–7 0 – 6.8 2.3 – 3.0 99 – 115 3.8 – 7.0 50 – 200 40 – 132 18 – 37 0.9 – 2.0 3.6 – 5.6 58 – 73 139 – 154 0.57 – 1.14 1.7 - 7.4 3.0 – 5.0 g/l U/l U/l umol/l umol/l mmol/l mmol/l mmol/l mmol/l mmol/l g/l mmol/l mmol/l g/l mmol/l mmol/l mmol/l mmol/l page 2 of 7 a) What is the problem list for this patient? b) What are the differential diagnoses for stunted growth? c) What is your interpretation of the blood results from this patient? d) How would you investigate this case further? a) The problem list for this patient can be summarised as:            Stunted growth Poor body condition Polyphagia Collapse Diarrhoea (intermittent) Glossitis/ulceration Pancytopenia Hypotension Hypothermia Tachycardia Tachypnoea The latter four problems could be combined together as hypovolaemic shock, given the response to fluid therapy. page 3 of 7 b) Potential differential diagnoses of stunted growth include:  Congenital portosystemic shunt – As this is a larger breed, an intrahepatic being more likely than an extra-hepatic  Pituitary dwarfism – This tends to lead to dogs which are proportionally smaller in size, alongside signs such as retention of puppy coat and dentition, high pitched bark and potentially behavioural changes. This condition is most commonly seen in the German Shepherd Dogs.  Congenital hypothyroidism – This often results in disproportionate dwarfism.  Chronic malabsorption as seen with a large parasitic burden, most often helminths.  Exocrine pancreatic insufficiency – The exocrine portion is no longer effective following immune-mediated destruction. Again seen most commonly in the German Shepherds, this often leads to polyphagia as a secondary effect of decreased absorption due to a lack of intrinsic factor and lack of nutrition digestion. Faeces are often seen as oily with this condition, the so called steatorrhea.  Congenital hypoadrenocorticism would be a potential cause for the nonspecific signs and lack of growth. This would be the atypical form, as the electrolytes are unaffected.  Nutritional deficiencies/malabsorptions, through either a general lack of intake (malnutrition), or inadequate vitamin or mineral content of the diet.  Inflammatory bowel disease remains a possibility but given the chronicity and age of onset of clinical signs, this is less likely.  Extra-gastrointestinal causes are also possible with patients suffering from conditions such as a patent ductus arteriosus or renal dysplasia occasionally presenting with stunted growth as the only sign initially page 4 of 7 c) There is a pancytopenia present. The platelet count is moderately low, but is not at a level likely to result in spontaneous or prolonged bleeding, which is typically quoted at less than 50 x 109/l. Both neutrophils and lymphocytes are decreased, although there is no evidence of a left shift present. The anaemia is most likely nonregenerative, although a pre-regenerative anaemia cannot be entirely discounted at this point. Whenever a single cell line is affected, there can be either a reduced production, sequestration or increased destruction/loss, or a combination there of. As all three lines are affected, this would be more consistent with a decrease in haematopoiesis, which the non-regenerative anaemia would support. The albumin is mildly reduced, which could be as a result of decreased production (hepatic disease) or increased loss (protein losing enteropathy, protein losing nephropathy, or loss into a third space such as during peritonitis). A third option is due to the role of albumin as a negative acute phase protein. During periods of stress or inflammation, the body down regulates the production of albumin and other homeostatic proteins, in favour of inflammatory proteins. This typically causes a mild hypoalbuminaemia. The alkaline phosphatase could be a reflection of cholestasis or an induced isoenzyme, but is more likely as a result of growth in a young dog. The triglycerides are marginally low, which could be due to recent Inappetence, or as so low could be within the normal range for this individual. d) Further investigation: Abdominal radiographs were unremarkable, aside from a lack of serosal detail due to limited intra-abdominal fat. Abdominal ultrasonography was also unremarkable, with no evidence of a portosystemic shunt identified (i.e. normal sized liver and kidneys, no evidence of turbulence within the caudal vena cava or portal veins). TLI was at the upper end of the reference limit, excluding exocrine pancreatic insufficiency as the underlying cause. An ACTH stimulation test was within normal limits, with a pre-stimulation value of 38.1 nmol/l and post of 461 nmol/l. A parvo virus snap test was negative page 5 of 7 Faecal analysis failed to culture any pathogens, there was no evidence of helminths and a Giardia ELISA was negative. In order to evaluate the absorptive capacity of the gastrointestinal system further, folate and cobalamin were measured. Folate was within normal limits at 8.3 µg/l (ref. 3.5 – 8.5), however cobalamin was markedly reduced at < 111 pmol/l (ref. 275 >). Based on the patient’s signalment, previous history and clinical signs, genetic testing was performed to assess the patient for congenital hypocobalaminaemia, or Imerslund-Gräsbeck syndrome. This was confirmed as the cause of the patient’s clinical signs. Summary: Cobalamin, or vitamin B12, is an essential vitamin obtained from the diet. Mammals are unable to synthesise cobalamin, it is instead produced by bacteria, which is obtained from either animal or dairy sources. Cobalamin has many essential functions and is particularly important in rapidly dividing cells; such as blood cell turnover, neuronal function and maintenance, gastrointestinal function alongside growth. Cobalamin is ingested bound to dietary protein. Within the stomach the protein is digested by pepsin and hydrochloric acid. This frees the cobalamin, which combines to R protein produced by the gastric mucosa. This complex then moves to the duodenum. At the level of the sphincter of Oddi, where the pancreatic duct inserts, a large number of proteases are released into the small intestine. This breaks down the R protein, once again freeing the cobalamin. Intrinsic factor, produced by both the pancreas and gastric mucosa in the dog, are released and once again combine with the cobalamin. This complex then transits through the small intestine until the level of the ileum. The ileum possesses a receptor (cubam) which is specific for the intrinsic factor-cobalamin complex. This receptor is composed of two components, amnionless and cubilin. Once this receptor becomes bound and activated, it is internalised and the cobalamin is taken to the sites it is necessary. In patients with Imerslund-Gräsbeck syndrome there is a homozygous mutation, resulting in a single base deletion leading to a premature stop codon. This results in an abnormal protein, making the receptor dysfunctional. The intrinsic factor-cobalamin complex can no longer bind to this abnormal receptor and are lost in the faeces, leading to a systemic cobalamin deficiency. Pups are born with a limited, maternally derived source of cobalamin. This will usually last until 10 – 16 weeks of age, after which they are no longer have adequate stores to support both maintenance and the marked growth that dogs undergo at this period of their life. This explains why the dog was a normal size at initial vaccinations. T page 6 of 7 In Beagles and Border Collies, it is a mutation in the area coding for cubilin. The condition is also seen in the Australian Shepherd and Giant Schnauzer, although in these patients it is a dysfunction in the amnionless portion of the receptor. Clinical signs in these patients are related to the effects upon rapidly dividing cells. This manifests as stunted growth, poor condition, pancytopenia, stomatitis/glossitis and intermittent pyrexia. As there is a cubam receptor within the kidneys proteinuria can also be seen, and this tends to persist despite treatment. In the Beagle and Border Collie, genetic testing can be used to identify the homozygous mutation in those affected. Unfortunately, this is not suitable in the Giant Schnauzer or Australian Shepherd. In these cases a surrogate marker can be used instead. Cobalamin is a co-factor in the conversion of methylmalonic acid (MMA) to Succinyl CoA. When cobalamin is deficient, there is a surplus of methylmalonic acid. When levels build up excessively it overspills into the urine where it can be detected. An elevated level supports the diagnosis, in combination with hypocobalaminaemia. The treatment of this condition requires the body’s store of cobalamin to be replenished. This must be administered parenterally as the ileum will be unable to absorb any from oral administration, and therefore must be bypassed. Subcutaneous is the usual route this is provided and supplementation will be necessary for the rest of the dog’s life. The maximal time between injections is variable, but typically is around 2 – 4 weeks, and as with diabetics, owners can be trained to perform this at home. Signs typically resolve rapidly, and in the case above the dog gained over 3 kg in weight over two weeks, with the PCV rising to 34%. References: Koyzyaki R, Cases O. 2013. Vitamin B12 absorption: Mammalian physiology and acquired and inherited disorders. Biochimie. 95: 1002 – 1007 Drogemuller M, Jagannathan V, Howard J et al. 2013. A frameshift in the cubilin gene (CUBN) in Beagles with Imerslund-Grasbeck sundrome (selective cobalamin malabsorption). Animal Genetics 45: 148 – 150 Fyfe JC, Hemker SL, Venta PJ. 2014. Selective intestinal cobalamin malabsorption with proteinuria (Imerslund-Grasbeck syndrome) in juvenile Beagles. Journal of Veterinary Internal Medicine 28: 356 – 362 Owczarek-Lipska M, Jagannathan V, Drogmuller C. 2013. A frameshift mutation in the cubilin gene (CUBN) in Border Collies with Imerslund-Grasbeck Syndrome (Selective cobalamin malabsorption). PLOS ONE Volume 8 Issue 4. page 7 of 7