R-binder deficiency. A clinically benign cause of cobalamin pseudodeficiency
R. Carmel
A patient with R-binder deficiency lacked this cobalamin-binding protein in
serum, saliva, gastric juice, and leukocytes, as demonstrated by
cobalamin-binding ability and radioimmunoassay. The patient's condition was
first detected because of a low serum cobalamin (vitamin B12) level. His
level of serum cobalamin, however, which was carried largely by
transcobalamin II, was not as decreased as in the initial cases reported
and was higher by some assays than by others. The demonstration of normal
bone marrow morphological appearance and deoxyuridine suppression test
findings, lack of attributable neurological dysfunction, and absence of
methylmalonic aciduria make clear that deficiency of R binder, whose
function is unknown, did not produce notable disturbance of cobalamin
metabolism. This entity is probably not as rare as originally thought. It
must be considered in the differential diagnosis of low serum cobalamin
levels, even among elderly patients, whose conditions often tend to be
automatically diagnosed as pernicious anemia.
