A calcium binding IgG myeloma protein

Ca(2+)-dependent anti-GQ1b antibody in GQ1b-seronegative Fisher syndrome and related disorders

Although serum IgG anti-ganglioside GQ1b antibody is the most specific biomarker for Fisher syndrome and its related disorders (FS-RD), 10%-30% of the patients are still negative in conventional assays ("GQ1b-seronegative") and the relationship between GQ1b-seropositive and -seronegative patients has been unclear. Some molecules require Ca(2+) cations to interact with their ligands (Ca(2+)-dependency). Here we have investigated whether Ca(2+)-dependency is also present in anti-GQ1b antibodies in FS-RD, especially in the GQ1b-seronegative patients and show that IgG antibodies against GQ1b-related antigens (isolated GQ1b and GQ1b-containing complexes) are detected Ca(2+)-dependently in the majority of GQ1b-seronegative patients with FS-RD. The Ca(2+)-dependent antibodies might react specifically with GQ1b-Ca(2+) conformation. This is the first demonstration of disease-related Ca(2+)-dependent antibodies in neurological field. GQ1b-related pathology would be involved in FS-RD more extensively than previously revealed.

Increased risk of citrate reactions in patients with multiple myeloma during peripheral blood stem cell leukapheresis

The citrate based anticoagulant ACD is commonly used in apheresis procedures. Due to its ability to decrease ionized calcium, citrate may cause unpleasant symptoms, such as paresthesias and muscle cramps, in patients undergoing therapeutic and donor apheresis. We noticed that patients with multiple myeloma (MM) undergoing autologous stem cell leukapheresis appeared to have more citrate reactions when compared to other patients undergoing the same procedure. A retrospective chart review was performed to evaluate 139 (of 151) consecutive patients with MM, amyloidosis, hematological and solid malignancies who had autologous peripheral blood stem cell collection between January 2007 and February 2008. Citrate reactions, ranging from mild (e.g., perioral tingling and parasthesias) to severe (e.g., nausea/vomiting and muscle cramps) were noted for 35 patients. Twenty-three of 63 patients with MM had documented citrate reactions, which was significantly higher than those with other hematological and solid malignancies (37% vs. 20%; P < 0.05, Relative Risk (RR) = 1.9). The severities of citrate reactions were the same in both groups; approximately 50% of patients in each group received i.v. calcium gluconate for treatment of hypocalcemia. No correlation between bisphosphonate therapy and citrate reactions were noted in our study group. Examination of available laboratory values related to calcium homeostasis, liver, and renal function failed to reveal a mechanism for the increase in citrate reactions observed. In summary, this single institution retrospective study indicates that patients with MM are more sensitive to citrate-induced hypocalcemia during leukapheresis when compared to patients with other hematological and solid malignancies. Strategies for decreasing citrate reactions (e.g., supplemental calcium and slowing return rates) should be considered for patient safety and comfort, especially in the MM population, on a prophylactic rather than reactive basis.

Protein precipitation as a possible important pitfall in the clinical chemistry analysis of blood samples containing monoclonal immunoglobulins: 2 case reports and a review of the literature

Two case reports are presented, both illustrating an analytical interference caused by monoclonal immunoglobulins. Falsely low results were obtained in the routine analysis of glucose, CRP and HDL-cholesterol. When analysing samples containing paraproteins, various problems can be encountered in the clinical laboratory: next to the antibody effect, pseudohyponatraemia, hyperviscosity, cryoglobulinaemia and gel formation have to be taken into account. In our two cases the interference was caused by paraprotein precipitation, causing an increased turbidity and an apparent increase of light absorbance at every wavelength due to light scattering, including the wavelengths used in the clinical chemistry assays. We review the literature on this sometimes overlooked interference in photometric/turbidimetric assays. This reaction is based on the insolubility of these proteins in specific physico-chemical circumstances in which many variables are involved, among others: pH and ionic strength, presence of preservatives and surfactants in the assays, pI and other specific properties of the monoclonal immunoglobulins. The complexity of the problem makes predicting or preventing this probably infrequent interference usually impossible. This artifact can cause both false positive and false negative results in multiple parameters (e.g. bilirubin, creatinine, iron, urea, uric acid), the most frequently reported analyte being phosphate. The Sia water test (Sia euglobulin precipitation test) can provide a first clue to a paraprotein aggregation; confirmation can be obtained by observing the time/ absorbance curves of the analysis, performing the test manually or setting up a serial dilution of the sample. The problem can be solved by avoiding the presence of the proteins in the assay, performing the analysis using an alternative method or diluting out the interference. Both laboratorians and clinicians should be aware of interferences in the clinical laboratory since the clinical consequences could be important.

Pseudohypercalcemia in an Elderly Patient with Multiplemyeloma: Report of a Case and Review of Literature

Hypercalcemia, a common complication of multiple myeloma, is primarily caused by increased bone resorption. The increase in total calcium is usually associated with an increase in the ionized calcium (Ca(I)), and the hypercalcemia is frequently symptomatic. Rarely, pseudohypercalcemia in multiple myeloma is caused by binding of calcium to the abnormal immunoglobulin. In this setting, the Ca(I) is normal. We describe a 90-year-old woman with an IgA-k myeloma who had substantial increases in the total calcium but normal levels of Ca(I). Clinicians should recognize this unusual phenomenon to avoid unnecessary and potentially toxic therapy.

Hypercalcaemia due to calcium binding by a polymeric IgA kappa-paraprotein

Total serum calcium concentration was raised in a 63-year-old lady with multiple myeloma and markedly elevated serum IgA kappa-paraprotein concentration. Symptoms of hypercalcaemia were absent, and serum ionized calcium was normal, suggesting calcium binding by the abnormal protein. This was demonstrated directly after isolation of the paraprotein and characterization of the calcium/protein interaction. After reduction of the paraprotein with mercaptoethanol, sodium dodecyl sulphate polyacrylamide gradient gel electrophoresis revealed two bands corresponding to light and heavy chains, but under non-reducing conditions the isolated paraprotein migrated in a series of bands, possibly representing polymeric forms of the basic immunoglobulin moiety.

Effects of intravenous etidronate disodium on skeletal and calcium metabolism

The induction of hypercalcemia in malignant disease is almost invariably associated with increased bone resorption. However, tumor-induced changes in bone formation and renal tubular resorption of calcium are also important factors that induce hypercalcemia in some patients. In addition, alterations in calcium fluxes to and from the extracellular fluid secondary to hypercalcemia are important in maintaining or aggravating the hypercalcemic effects of increased bone resorption. These factors significantly affect the responses to treatment of hypercalcemia with inhibitors of bone resorption. This study examined the relative importance of these factors and the effects of intravenous etidronate disodium (etidronate) in neoplastic bone disease with and without hypercalcemia and in Paget's disease of bone. It is concluded that intravenous etidronate is an effective inhibitor of bone resorption, which accounts in large measure for its effects on serum calcium concentrations. These studies of etidronate in hypercalcemia suggest the response is sustained for several weeks.

A human myeloma immunoglobulin G binding four moles of calcium associated with asymptomatic hypercalcemia

A calcium-binding immunoglobulin G (IgG1 lambda RUP) was identified in the serum of a patient with multiple myeloma, asymptomatic hypercalcemia, and a normal ionized serum calcium. Calcium binding by IgGRUP was confirmed by two-dimensional electrophoresis with calcium-45 and equilibrium dialysis. Amino acid analyses indicated an unusually high number of glutamic (or glutamine) residues in the L chain and Fab fragment but no detectable gamma-carboxyglutamic acid. As determined by equilibrium dialysis with 45Ca, the intact IgGRUP and its Fab fragments bound calcium at an optimum pH of 7.4. There was minimal binding of calcium to H chains and no binding by L chains or the Fc fragment. Recombination of H and L chains partially restored the binding activity. By Scatchard analysis, the binding affinity (Kd) of IgGRUP was 1.7 X 10(-3) M and the binding capacity was 4 mol of calcium/mol of IgG. The binding of 4 mol of calcium/mol of IgG is twice that reported previously for two other calcium-binding myeloma proteins and suggests unique properties of IgGRUP.

Human myeloma light chains with increased molecular weight: high frequency among lambda chains

The discovery of a human myeloma protein comprising a kappa L-chain with an increased mol. wt of 30,000) (Bouvet et. al., 1980) prompted investigations on the incidence of such heavier L-chains among other human myeloma proteins. In 105 samples examined, 34 were found to have L-chains heavier than normal (23,000-24,000), ranging from 25,000 up to 31,000, and five of lighter mol. wt (21,000-22,000). These mol. wt abnormalities were detected by electrophoresis in sodium dodecyl sulfate 10% polyacrylamide gels (SDS-PAGE) after reduction with 2-mercaptoethanol. The mol. wt of three of the heavier kappa or lambda chains was also estimated by filtration through a Sephadex G100 column and by sedimentation equilibrium. All three methods indicated a mol. wt increase of about 15-25% as compared with the usual mol. wt. The distribution of the high mol. wt chains among all L-chains examined was found to be 11 out of 62 kappa chains (17.7%) and 23 out of 43 lambda chains (53%) (P less than 0.001). A preferential association of such L-chains with H-chains producing multiple bands in SDS-PAGE (P less than 0.01) and an association between multiple L-chain and multiple H-chain band (P less than 0.05) were also observed. In contrast, no abnormal L-chain was found in immunoglobulins from normal subjects. Spontaneous degradation of the normal H-chains sometimes yielded fragments of 30,000 mol. wt. These fragments were easily distinguishable from abnormal L-chains. The nature of extra mol. wt in heavy L-chains was investigated for the presence of carbohydrate moiety. Four large and three normal size L-chains were examined for amino-sugar and sialic acid content. A small amount (one residue per molecule) of amino-sugar was detected only in two normal and two heavy L-chains, whereas sialic acid was only found in the heaviest (27,000-30,000) L-chains (Lh) and in small percentage (one or two residues per molecule). Total sugar estimation in one Lh chain indicated a proportion not exceeding three or four residues per L-chain (mol. wt 1,000) and this is insufficient to explain the 15-25% (3,600-6,000) mol. wt increase. It is therefore possible that, at least in some heavy myeloma L-chains, an additional peptide is expressed. Whatever the nature of the increase it would be of interest to elucidate whether this is a marker of malignant process or of an intermediate step of normal Ig synthesis.

Non symptomatic hypercalcemia in a myeloma patient

An asymptomatic hypercalcemic IgG-Kappa myeloma patient is presented. A calcium-IgG complex was isolated and purified from the serum by column chromatography. Following further purification on a Sepharose protein A column, the IgG-Kappa molecule did not contain any detectable amount of calcium, indicating that calcium is loosely bound to IgG. The monoclonal IgG demonstrated a strong calcium binding capacity in vitro. The calcium-IgG complex in the serum was shown not to be saturated and thus could absorb more ionized calcium. In view of the presence of an abnormal monoclonal IgG capable of binding excess calcium, and the fact that the asymptomatic patient did not respond to the antihypercalcemic drugs, the treatment was stopped.