Inheritance of transcobalamin II (TC II) in two families with TC II deficiency and related immunodeficiency

Transcobalamin II (TC II) is an essential transport protein for vitamin B₁₂ in blood. TC II can be separated into isoproteins by polyacrylamide gel electrophoresis. This method was used in combination with a specific radioimmunosorbent technique to evaluate genetic variants and inheritance of TC II-deficient genes in relatives of two children with congenital TC II deficiency. Both patients presented with impairment of haematopoietic and immunological functions. Seven heterozygous individuals for TC II deficiency, who are clinically normal, were detected in the two families. Two out of seven could be identified unambiguously by TC II isoprotein analysis, as carriers of a deficient gene, which does not express functional TC II. Application of this new method to detect heterozygous carriers of the deficient gene provides a valuable addition to genetic counselling.