OMIA:000565-9615 : Intestinal cobalamin malabsorption, AMN-related in Canis lupus familiaris (dog)

Categories: Haematopoietic system phene

Links to possible relevant human trait(s) and/or gene(s) in OMIM: 618882 (trait) , 605799 (gene)

Mendelian trait/disorder: yes

Mode of inheritance: Autosomal recessive

Considered a defect: yes

Key variant known: yes

Year key variant first reported: 2005

Cross-species summary: Imerslund-Gräsbeck syndrome (IGS2); megaloblastic anemia, Norwegian type

Species-specific description: Intestinal cobalamin malabsorption is a metabolic disorder characterized by failure to thrive, neutropenia, decreased serum cobalamin (Cbl), and nonregenerative anemia. Other signs include chronic inappetance, megaloblastic changes of the bone marrow, methylmalonic aciduria, and homocysteinemia. It occurs in the giant schnauzer, Australian shepherd, border collie, Hungarian komondor, and beagle. In giant schnauzers and Australian shepherds intestinal cobalamin malabsorption is due to absence of receptors for the intrinsic factor-Cbl complex at the brush border of enterocytes in the ileum. A specific defect has not yet been demonstrated in other breeds. The mode of inheritance is autosomal recessive. The two known causative mutations are a deletion in AMN in the giant schnauzer, and a nucleotide substitution in AMN in the Australian shepherd. Tests are available to detect the known causative mutations. Parents and siblings of affected dogs should be tested. Breeding of affected dogs is not recommended. Carriers should be bred only to clinically normal dogs demonstrated to be non carriers. Entry edited by John C. Fyfe, D.V.M., Ph. D. Intestinal cobalamin malabsorption can be caused by mutations in the AMN gene (this entry) or by mutations in the CUBN gene [OMIA 001786-9615].

Inheritance: Autosomal recessive

Mapping: Using a whole-genome scan with microsatellite markers in a pedigree of 88 dogs of known disorder phenotype, He et al. (2003) mapped this disorder to a 4Mb interval on chromosome CFA8. The authors noted that this region of CFA8 has conserved synteny with the region of chromosome HSA14q that harbours a very strong comparative candidate gene, namely AMN (amnionless), mutations in which cause the same clinical disorder in humans.

Molecular basis: By adopting a comparative positional cloning approach, having established AMN as a very strong comparative positional candidate gene (see Mapping section above), He et al. (2005) showed that the causative mutation in Giant Schnauzers is an "in-frame deletion of 33 nucleotides in exon 10 of AMN . . . [namely] c.1113_1145del"; the causative mutation in Australian shepherds is "a G>A transition at position 3 of the cDNA sequence [of AMN] (c.3G>A), thereby disrupting the Kozak consensus sequence for translation initiation".

Clinical features: Signs begin around 6 to 12 weeks of age, and include failure to thrive and chronic inappetance. Affected animals also demonstrate neutropenia with hypersegmentation, nonregenerative anemia with anisocytosis and poikilocytosis, megaloblastic changes of the bone marrow, decreased serum Cbl concentrations, methylmalonic aciduria, and homocysteinemia. These animals have normal renal function, but low-molecular weight urinary protein excretion (Fyfe et al., 1991).

Pathology: In normal dogs, Cbl is ingested in the diet and binds to intrinsic factor, a glycoprotein made by the gastric mucosa and the pancreatic duct epithelium. The complex of intrinsic factor (IF) and Cbl is absorbed through binding receptors on enterocytes in the distal jejunum and ileum. Signs of intestinal cobalamin malabsorption are due to absence of receptors for the IF-Cbl complex at the brush border (Fyfe et al., 1991). Affected dogs have one of two demonstrated mutations in the gene coding for amnionless, a protein that complexes with cubilin to ensure apical membrane localization of IF-Cbl receptors in enterocytes. It also regulates endocytic functions. Without functional amnionless, the IF-Cbl receptors do not localize to the brush-border, and dogs cannot absorb cobalamin (Fyfe et al., 2003). Dogs are born with cobalamin stores, but they are rapidly used up during postnatal growth unless replaced from the diet. This is when signs become apparent (Fyfe et al., 1991).

Control: Parents and siblings of affected dogs should be tested. Breeding of affected is not recommended. Carriers should only be bred to tested dogs that are not carriers.

Genetic testing: A DNA test for the disorder is included in the OFA's list at, which directs enquiries to PennGen at the University of Pennsylvania (

Breeds: Australian Shepherd (Dog) (VBO_0200095), Giant Schnauzer (Dog) (VBO_0200604), Komondor (Dog) (VBO_0200779).
Breeds in which the phene has been documented. (If a likely causal variant has been documented for the phene, see the variant table breeds in which the variant has been reported).

Associated gene:

Symbol Description Species Chr Location OMIA gene details page Other Links
AMN amnion associated transmembrane protein Canis lupus familiaris - no genomic information (-..-) AMN Homologene, Ensembl , NCBI gene


By default, variants are sorted chronologically by year of publication, to provide a historical perspective. Readers can re-sort on any column by clicking on the column header. Click it again to sort in a descending order. To create a multiple-field sort, hold down Shift while clicking on the second, third etc relevant column headers.

WARNING! Inclusion of a variant in this table does not automatically mean that it should be used for DNA testing. Anyone contemplating the use of any of these variants for DNA testing should examine critically the relevant evidence (especially in breeds other than the breed in which the variant was first described). If it is decided to proceed, the location and orientation of the variant sequence should be checked very carefully.

Since October 2021, OMIA includes a semiautomated lift-over pipeline to facilitate updates of genomic positions to a recent reference genome position. These changes to genomic positions are not always reflected in the ‘acknowledgements’ or ‘verbal description’ fields in this table.

OMIA Variant ID Breed(s) Variant Phenotype Gene Allele Type of Variant Source of Genetic Variant Reference Sequence Chr. g. or m. c. or n. p. Verbal Description EVA ID Year Published PubMed ID(s) Acknowledgements
639 Giant Schnauzer (Dog) Intestinal cobalamin malabsorption, AMN-related AMN deletion, gross (>20) Naturally occurring variant CanFam3.1 8 g.70807271_70807303del c.1113_1145del p.(G372_A382del) NM_001002960.1; NP_001002960.1 2005 15845892 Genomic position in CanFam3.1 provided by Robert Kuhn and Mateo Etcheveste.
426 Australian Shepherd (Dog) Intestinal cobalamin malabsorption, AMN-related AMN start-lost Naturally occurring variant ROS_Cfam_1.0 8 g.71077084G>A c.3G>A p.(M1?) NM_001002960.1; NP_001002960.1 2005 15845892

Cite this entry

Nicholas, F. W., Tammen, I., & Sydney Informatics Hub. (2013). OMIA:000565-9615: Online Mendelian Inheritance in Animals (OMIA) [dataset].


Note: the references are listed in reverse chronological order (from the most recent year to the earliest year), and alphabetically by first author within a year.

2020 Kather, S., Grützner, N., Kook, P.H., Dengler, F., Heilmann, R.M. :
Review of cobalamin status and disorders of cobalamin metabolism in dogs. J Vet Intern Med 34:13-28, 2020. Pubmed reference: 31758868. DOI: 10.1111/jvim.15638.
2015 Gold, A.J., Scott, M.A., Fyfe, J.C. :
Failure to thrive and life-threatening complications due to inherited selective cobalamin malabsorption effectively managed in a juvenile Australian shepherd dog. Can Vet J 56:1029-34, 2015. Pubmed reference: 26483576.
2005 He, Q., Madsen, M., Kilkenney, A., Gregory, B., Christensen, E.I., Vorum, H., Højrup, P., Schäffer, A.A., Kirkness, E.F., Tanner, S.M., de la Chapelle, A., Giger, U., Moestrup, S.K., Fyfe, J.C. :
Amnionless function is required for cubilin brush-border expression and intrinsic factor-cobalamin (vitamin B12) absorption in vivo. Blood 106:1447-53, 2005. Pubmed reference: 15845892. DOI: 10.1182/blood-2005-03-1197.
2004 Fyfe, J.C., Madsen, M., Højrup, P., Christensen, E.I., Tanner, S.M., de la Chapelle, A., He, Q., Moestrup, S.K. :
The functional cobalamin (vitamin B12)-intrinsic factor receptor is a novel complex of cubilin and amnionless. Blood 103:1573-9, 2004. Pubmed reference: 14576052. DOI: 10.1182/blood-2003-08-2852.
2003 He, Q., Fyfe, JC., Schaffer, AA., Kilkenney, A., Werner, P., Kirkness, EF., Henthorn, PS. :
Canine Imerslund-Grasbeck syndrome maps to a region orthologous to HSA14q. Mamm Genome 14:758-64, 2003. Pubmed reference: 14722725. DOI: 10.1007/s00335-003-2280-1.
2000 Fordyce, H.H., Callan, M.B., Giger, U. :
Persistent cobalamin deficiency causing failure to thrive in a juvenile beagle Journal of Small Animal Practice 41:407-410, 2000. Pubmed reference: 11023127.
1991 Batt, RM., Horadagoda, NU., Simpson, KW. :
Role of the pancreas in the absorption and malabsorption of cobalamin (vitamin B-12) in dogs. J Nutr 121:S75-6, 1991. Pubmed reference: 1941244.
Fyfe, J.C., Giger, U., Hall, C.A., Jezyk, P.F., Klumpp, S.A., Levine, J.S., Patterson, D.F. :
Inherited Selective Intestinal Cobalamin Malabsorption and Cobalamin Deficiency in Dogs Pediatric Research 29:24-31, 1991. Pubmed reference: 1848001.
Fyfe, J.C., Ramanujam, K.S., Ramaswamy, K., Patterson, D.F., Seetharam, B. :
Defective Brush-Border Expression of Intrinsic Factor- Cobalamin Receptor in Canine Inherited Intestinal Cobalamin Malabsorption Journal of Biological Chemistry 266:4489-4494, 1991. Pubmed reference: 1999430.

Edit History

  • Created by Frank Nicholas on 13 Jul 2011
  • Changed by Martha MaloneyHuss on 16 Aug 2011
  • Changed by Martha MaloneyHuss on 23 Aug 2011
  • Changed by Frank Nicholas on 09 Feb 2012
  • Changed by Frank Nicholas on 21 Oct 2012
  • Changed by Tosso Leeb on 18 Apr 2013
  • Changed by Tosso Leeb on 23 Apr 2013