Hereditary cobalamin deficiency is suspected in the Border Collie breed. Diagnosis is based on hypocobalaminemia, hyperhomocysteinemia and methylmalonic aciduria. Goals of the study were (1) to establish reference values for the blood concentrations of cobalamin and homocysteine and for the concentration of urinary methylmalonic acid and (2) to screen a larger Border Collie population with the aforementioned markers.
Cobalamin, homocysteine and methylmalonic acid were measured using an automated chemiluminescence assay, HPLC with fluorimetric detection and gas chromatography / mass spectrometry. A total of 113 Border Collies and 35 healthy dogs of different breeds were examined. Four Border Collies suffered from cobalamin deficiency with the following concentrations: cobalamin < 150 (reference range (ref), 261–1001) ng/L, homocysteine 40–81.6 (ref, 4.3–18.4) μmol/L, and methylmalonic acid 1800–6665 (ref, < 4.2) mmol/mol. Unexpectedly 37.7% of Border Collies with normal cobalamin had significantly higher methylmalonic acid concentrations (P < 0.0001). In conclusion, the simultaneous finding of methylmalonic aciduria in Border Collies with normal cobalamin concentrations in addition to Border Collies with clinicopathologic findings of cobalamin deficiency is surprising and suggests two different defects. Future studies investigating the absorption process as well as the metabolic pathway of cobalamin are warranted.