Simultaneous increases in both MMA and total Hcy (tHcy) are seen in inherited intracellular cobalamin defects, vitamin [B.sub.12] deficiency, Imerslund-Grasbeck syndrome, and transcobalamin II deficiency
. Patients with inherited intracellular cobalamin defects usually present with higher concentrations of MMA and/or tHcy than patients with vitamin [B.sub.12] deficiency.
haemolysis.18 Vitamin B12 levels may be reported as normal or elevated in myeloproliferative disorders liver disease congenital transcobalamin II deficiency
intestinal bacterial overgrowth and antecedent administration of vitamin B12.18
These causes include (a) nutritional vitamin B12 deficiency, (b) acquired and inherited intrinsic factor deficiency, (c) selective intestinal malabsorption of vitamin B12,(d) transcobalamin II deficiency
, (e)mutations in genes responsible for defects in intracellular methylcobalamin synthesis [MTRR (5-methyltetrahydrofolate-homocysteine methyltransferase reductase), MTR (5-methyltetrahydrofolate-homocysteine methyltransferase); also referred to as complementation groups cblE and cblG, respectively], and (f) N(5,10)-meth ylenetetrahydrofolate reductase deficiency.
Neonatal megaloblastic anemia due to inherited transcobalamin II deficiency
in two siblings.
Hereditary partial transcobalamin II deficiency
with neurologic, mental, and hematologic abnormalities in children and adults.
Long-term follow up of patients with transcobalamin II deficiency
. Arch Dis Child 1995;72:237-8.