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Transcobalamin (TC) I deficiency, like the function of TC I itself, is incompletely understood. It produces low serum cobalamin levels indistinguishable from those of true cobalamin deficiency. Diagnosis is especially elusive when TC I deficiency is mild. To provide new, more substantive definition, the TCN1 gene was examined in two well-characterised families that included members with both severe and mild TC I deficiencies. A severely deficient proposita with undetectable TC I levels displayed compound heterozygosity for two mutations, each causing a premature stop codon. Relatives in both families who had mildly low or low-normal plasma levels of TC I and cobalamin were heterozygous for one or the other of these mutations. An unrelated patient with mild TC I deficiency and unknown familial TC I and cobalamin status was then tested and found to be similarly heterozygous for one of the mutations. The two nonprivate mutations identify a genetic basis for TC I deficiency for the first time. They also add new approaches to studying mild and severe TC I deficiency and to reducing confusion of its low cobalamin levels with those of cobalamin deficiency and its often dramatically different prognosis and management. [ABSTRACT FROM AUTHOR]

Focuses on genetic polymorphisms associated with the diminished activity of 5,10-methylenetetrahydrofolate reductase in the clinical manifestations of cobalamin deficiency. Polymerase chain reaction; Lack of association between mutations and neurological status.

Presents a diagnosis on cobalamin deficiency. Sensitivity of urinary methylmanolic acid tests; Measurement of MMA through ether extraction and gas chromatography; Misinterpretations of the reduction of MMA levels following cobalamin therapy.

Examines the efficacy of methylmalonic acid (MMA) as a marker of cobalamin deficiency. Validity of biochemical markers; Details of an experimental model using totally gastrectmomized rat; Incidence of severe anemia and spongiosus myeloneuropathy.