[Immune deficiencies secondary to enzymopathies]

Immune deficiencies secondary to enzyme deficiencies that affect purine and pyrimidine metabolism account for approximately 50% of severe immune deficiencies inherited as a recessive autosomal trait. Adenosine deaminase (ADA) deficiency is the most common and also the earliest and most severe of these diseases. ADA deficiency is responsible for a severe combined immune deficiency with alymphocytosis and often characteristic bone and cartilage abnormalities. The treatment of choice is transplantation of compatible bone marrow; in cases where this has not been feasible, replacement therapy with the enzyme coupled to polyethylene glycol has yielded promising results. Purine nucleoside phosphorylase (PNP) deficiency is responsible for an isolated T cell defect. Low serum uric acid levels are highly suggestive of PNP deficiency. Bone marrow transplantation is indicated. In both diseases, the immune deficiency is due to the toxic effect of purine deoxynucleosides on lymphoid cells. Enzyme deficiencies that directly or indirectly affect pyrimidine metabolism (orotate phosphoribosyltransferase and methionine synthase deficiencies) are exceedingly rare and only inconsistently produce an immune defect (involving T cells).

Combined congenital deficiencies of intrinsic factor and R binder

Coexisting deficiencies of both intrinsic factor (IF) and R binder were identified in an Algerian boy who presented with severe megaloblastic anemia, growth retardation, and neurologic dysfunction with typical features of subacute combined degeneration of the spinal cord. The anemia responded completely to cyanocobalamin and folic acid. IF was absent from gastric juice, but acid secretion and gastric mucosa were normal. R binders were absent from gastric juices as well as from serum, saliva, and polymorphonuclear leukocytes. The patient's father exhibited absence of R binder in his serum with a low serum vitamin B12 level and was asymptomatic. This unique case of simultaneous IF and R binder deficiencies suggests a genetic association between these two functionally and immunologically dissimilar, but structurally close vitamin B12-binding proteins.

Transcobalamin II deficiency: long-term follow-up of two cases

Two Spanish siblings, a boy and girl, with transcobalamin II (TCII) deficiency are described. Both have grown and developed mentally normally after 10 years of vitamin B12 therapy. Two other siblings died soon after birth and it is almost certain that they also suffered from TCII deficiency.

Expression of transcobalamin II by amniocytes

Children with a genetic absence of transcobalamin 2 (TC2) are clinically asymptomatic at birth but develop severe megaloblastic anemia early in life. We have examined the incorporation of [57Co]-CN-B12 in the absence of any exogenous source of TC2 in control amniotic fluid derived cells and cultured diploid fibroblasts, and in fibroblasts from a patient with TC2 deficiency. Both control fibroblasts and amniocytes incorporated labelled B12 into TC2-B12, and the proportion of labelled TC2-B12 could be increased by growing cells in the presence of chloroquine which prevents intralysosomal hydrolysis of the TC2-B12 complex. In contrast, fibroblasts from the patient with TC2 deficiency incorporated almost no label as TC2-B12. These studies suggest that TC2 deficiency either due to aberrant production of TC2 or because of the production of an abnormal TC2 which does not bind B12 can be diagnosed before birth.

Homozygous transcobalamin II deficiency maintained on oral hydroxocobalamin

A case of transcobalamin II (TCII) deficiency in which a total absence of TCII was demonstrated both functionally and immunologically is reported. Unlike previously described patients, this child has been maintained on oral hydroxocobalamin, 2 mg daily, without any parenteral supplementation for the last five years. At the age of six years her development is normal and her health is good. Plasma cobalamin levels are in the range of 3,000 ng/L and most of this appears to be bound to a molecule, which on gel filtration, elutes with albumin. In an extended family study, a clear separation of heterozygotes from both the propositus and from normal subjects suggests that the underlying defect in this condition is confined to a single gene.

Synthesis and secretion of the human vitamin B12-binding protein, transcobalamin II, by cultured skin fibroblasts and by bone marrow cells

Human skin fibroblasts and bone marrow cells were tested for their ability to synthesize the cobalamin-binding protein transcobalamin II. Cobalamin binders secreted in the media of cultured fibroblasts and of dextran-sedimented bone marrow cells in liquid culture could be identified as transcobalamin II on the basis of immunological, electrophoretical and chromatographical identity with serum transcobalamin II. The net secretion of transcobalamin II increased linearly with time of culture, up to 30 days after confluence. The reversible inhibition of transcobalamin II secretion by cycloheximide demonstrated that human fibroblasts are capable of de novo transcobalamin II synthesis. Addition of cyanocobalamin to the fibroblast culture medium induced a reduction of transcobalamin II net secretion, most likely due to preferred uptake of transcobalamin II saturated with cobalamin, as opposed to unsaturated protein. Addition of lysozymal enzyme inhibitors, ammonium chloride and chloroquine, resulted in a markedly increased secretion of transcobalamin II. In the culture medium of fibroblasts, obtained from two transcobalamin II-deficient patients, functionally deficient transcobalamin II was demonstrated on the basis of strongly reduced secretion of immunoreactive transcobalamin II, and the absence of apotranscobalamin II. Individual phenotypes in the culture media of the fibroblasts and bone marrow cells were identical to the corresponding serum transcobalamin II types.

The pharmacologic treatment of portal hypertension

Surgical procedures that lower portal pressure, such as portacaval shunts, prevent variceal hemorrhage. Portal hypertension is the result of increased flow and increased resistance in the portal system. Pharmacologic therapy is aimed at altering these factors by the use of vasoconstrictors to reduce flow and vasodilators to decrease resistance. The current status of pharmacologic agents to achieve these effects is reviewed.

Immunodeficiency syndromes and the gut

The gastrointestinal tract in immunodeficiency disorders is involved with diseases similar to those seen in the immune competent. However, in some immune deficient states the incidence of gastrointestinal disease is high whereas in others it is no different than in the general population. This review clarifies the unique and specific abnormalities seen in immune deficient states and stresses the newest recognised abnormalities. It highlights the fact that the most frequent and severe abnormalities occur in patients with combined immune deficient states.

Hereditary transcobalamin II deficiency with subnormal serum cobalamin levels

An infant with transcobalamin II deficiency had the unusual feature of a low serum cobalamin level. Moreover, the level did not rise greatly with cobalamin therapy. Clinically, the features of the infant's illness were unexceptional other than the somewhat delayed onset of symptoms at 3 1/2 months of age. In addition, the patient's impaired antibody response to specific antigen challenge was not completely corrected following cobalamin therapy, and this result contrasts with the findings in the only previous examination of this feature of the disorder. As in previous cases, the transcobalamin II deficiency was accompanied by findings in the serum of complexing of the patient's R binder and the relative prominence of a cobalamin-binding peak eluting at a molecular weight of approximately 70,000 on Sephadex G-200 gel chromatography. In addition, the total serum R binder (free and complexed) level was low. This case demonstrates that transcobalamin II deficiency should be considered in any infant with a low serum cobalamin level in the first few months of life.

Congenital transcobalamin II deficiency presenting atypically with a low serum cobalamin level: studies demonstrating the coexistence of a circulating transcobalamin I (R binder) complex

A case of transcobalamin II deficiency with several unique features is described. The clinical presentation was typical, except for a slightly delayed age at presentation and the occurrence of apparent neurologic dysfunction from the beginning. The unusual biochemical feature was a low serum cobalamin level (97 pg/ml). Several cobalamin-binding protein abnormalities coexisted and antedated cobalamin therapy. Chief among these was the complexing of all serum R binder (transcobalamin I), leaving the patient with no detectable R binder. This defect appeared to be transient. Noteworthy, too, was a prominent binder of 70,000 mol wt that also carried the bulk of his serum cobalamin after therapy; it was prominent in his presumably heterozygous relatives too. The interrelationship between all these abnormalities is intriguing but unclear. The abnormality in transcobalamin II deficiency is clearly not limited solely to deficiency of transcobalamin II. It is also evident that this entity must now be considered in the differential diagnosis of low serum cobalamin levels in infancy.