How we diagnose and manage altered oxygen affinity hemoglobin variants.

Altered oxygen affinity variant hemoglobins (Hbs) are caused by mutations of the globin genes. Changes in Hb oxygen affinity shift the oxygen dissociation curve, and can be identified by abnormal p50 measurements of patient red blood cells. Variants are categorized as either low oxygen affinity (high p50) or high oxygen affinity (low p50). Accurate diagnosis requires recognition of typical clinical and laboratory findings. In this case-based review, we present two patients with altered oxygen affinity variants, illustrating barriers to prompt and accurate diagnosis, and issues in management. We then review pathophysiology, diagnostic tests, clinical features, and management strategies.

Clinical evaluation of a hemochromatosis next-generation sequencing gene panel.

BACKGROUND: Next-generation sequencing of an iron metabolism gene panel could identify pathogenic mutations, improving on standard hemochromatosis genetic testing and providing a molecular diagnosis in patients with suspected iron overload. METHODS: A next-generation sequencing panel of 15 genes with known roles in iron metabolism was constructed. A total of 190 patients were sequenced: 94 from a tertiary hemochromatosis clinic and 96 submitted for HFE testing with biochemical evidence of iron overload [elevated ferritin (>450 µg/L) or transferrin saturation (>55%)] obtained from a chart review. RESULTS: From the hemochromatosis clinic cohort, six patients were diagnosed with non-HFE hemochromatosis due to homozygous hemojuvelin (HFE2) mutations. Ten additional heterozygous pathogenic mutations were observed. From the chart review cohort, a C-terminus ferritin light chain (FTL) frameshift mutation was observed consistent with neuroferritinopathy. Heterozygous deletion of HFE2 and four additional rare pathogenic or likely pathogenic heterozygous mutations were identified in seven patients. CONCLUSIONS: An iron metabolism gene panel provided a molecular diagnosis in six patients with non-HFE iron overload and is suitable for diagnostic purposes in exceptional cases in specialized clinics. Further research will be required to assess the modifier effect of rare heterozygous mutations in iron metabolism genes.

A 13-question approach to resolving serological discrepancies in the transfusion medicine laboratory.

Laboratory professionals, consultants, and treating physicians may encounter discrepancies in serological testing results for numerous reasons; identifying the reason(s) for the presence of an unexpected antibody or antigen can be challenging. A question-based approach can be useful in identifying the underlying cause of the discrepancy. We describe a new approach to serological problems in a transfusion-service laboratory. The approach we outline herein is targeted towards a general transfusion medicine service, rather than a center that offers complex antibody investigations using specialized techniques. This question-based problem-solving approach considers patient factors including diagnosis, transfusion history, previous pregnancies, and medication history, along with serological test results: ABO and Rh groups, direct and indirect antiglobulin tests, reacting temperature of the antibody, effect of enzyme treatment of cells, strength of reactivity, and antibody reactivity with umbilical cord cells. We also demonstrate the usefulness of this approach through a case scenario.

Periprocedural heparin bridging in patients receiving vitamin K antagonists: systematic review and meta-analysis of bleeding and thromboembolic rates.

BACKGROUND: Periprocedural bridging with unfractionated heparin or low-molecular-weight heparin aims to reduce the risk of thromboembolic events in patients receiving long-term vitamin K antagonists. Optimal periprocedural anticoagulation has not been established. METHODS AND RESULTS: MEDLINE, EMBASE, and Cochrane databases (2001-2010) were searched for English-language studies including patients receiving heparin bridging during interruption of vitamin K antagonists for elective procedures. Data were independently collected by 2 investigators (κ=0.90). The final review included 34 studies with 1 randomized trial. Thromboembolic events occurred in 73 of 7118 bridged patients (pooled incidence, 0.9%; 95% confidence interval [CI], 0.0.0-3.4) and 32 of 5160 nonbridged patients (pooled incidence, 0.6%; 95% CI, 0.0-1.2). There was no difference in the risk of thromboembolic events in 8 studies comparing bridged and nonbridged groups (odds ratio, 0.80; 95% CI, 0.42-1.54). Bridging was associated with an increased risk of overall bleeding in 13 studies (odds ratio, 5.40; 95% CI, 3.00-9.74) and major bleeding in 5 studies (odds ratio, 3.60; 95% CI, 1.52-8.50) comparing bridged and nonbridged patients. There was no difference in thromboembolic events (odds ratio, 0.30; 95% CI, 0.04-2.09) but an increased risk of overall bleeding (odds ratio, 2.28; 95% CI, 1.27-4.08) with full versus prophylactic/intermediate-dose low-molecular-weight heparin bridging. Low-thromboembolic-risk and/or non-vitamin K antagonist patient groups were used for comparison. Study quality was poor with heterogeneity for some analyses. CONCLUSIONS: Vitamin K antagonist-treated patients receiving periprocedural heparin bridging appear to be at increased risk of overall and major bleeding and at similar risk of thromboembolic events compared to nonbridged patients. Randomized trials are needed to define the role of periprocedural heparin bridging.

Specificity in substrate and cofactor recognition by the N-terminal domain of the chaperone ClpX.

Clp ATPases are a unique group of ATP-dependent chaperones supporting targeted protein unfolding and degradation in concert with their respective proteases. ClpX is a representative member of these ATPases; it consists of two domains, a zinc-binding domain (ZBD) that forms dimers and a AAA+ ATP-binding domain that arranges into a hexamer. Analysis of the binding preferences of these two domains in ClpX revealed that both domains preferentially bind to hydrophobic residues but have different sequence preferences, with the AAA+ domain preferentially recognizing a wider range of specific sequences than ZBD. As part of this analysis, the binding site of the ClpX dimeric cofactor, SspB2, on ZBD in ClpX was determined by NMR and mutational analysis. The SspB C terminus was found to interact with a hydrophobic patch on the surface of ZBD. The affinity of SspB2 toward ZBD2 and the geometry of the SspB2-ZBD2 complex were investigated by using the newly developed quantitative optical biosensor method of dual polarization interferometry. The data suggest a model for the interaction between SspB2 and the ClpX hexamer.