Plasmodium falciparum adhesion domains linked to severe malaria differ in blockade of endothelial protein C receptor.

Cytoadhesion of Plasmodium falciparum-infected erythrocytes to endothelial protein C receptor (EPCR) is associated with severe malaria. It has been postulated that parasite binding could exacerbate microvascular coagulation and endothelial dysfunction in cerebral malaria by impairing the protein C-EPCR interaction, but the extent of binding inhibition has not been fully determined. Here we expressed the cysteine-rich interdomain region (CIDRα1) domain from a variety of domain cassette (DC) 8 and DC13 P. falciparum erythrocyte membrane protein 1 proteins and show they interact in a distinct manner with EPCR resulting in weak, moderate and strong inhibition of the activated protein C (APC)-EPCR interaction. Overall, there was a positive correlation between CIDRα1-EPCR binding activity and APC blockade activity. In addition, our analysis from a combination of mutagenesis and blocking antibodies finds that an Arg81 (R81) in EPCR plays a pivotal role in CIDRα1 binding, but domains with weak and strong APC blockade activity were distinguished by their sensitivity to inhibition by anti-EPCR mAb 1535, implying subtle differences in their binding footprints. These data reveal a previously unknown functional heterogeneity in the interaction between P. falciparum and EPCR and have major implications for understanding the distinct clinical pathologies of cerebral malaria and developing new treatment strategies.

A rare primary immunodeficiency.

A 9-year-old girl presented with failure to thrive, chronic mucopurulent nasal discharge, recurrent skin pustules and recurrent episodes of purulent ear discharge since 2 years of age. She had coarse facial features with extensive eczema, multiple pyoderma scars, florid dental caries, retained primary dentition, hypermobile joints and a woody induration of the vulva. Autosomal dominant hyper-IgE syndrome was suspected and confirmed by very high serum IgE levels. Vulval biopsy revealed a premalignant condition. STAT 3 mutation, which is usually responsible for this condition, was not found in our case, indicating an as yet unidentified mutation. The child also had unusual features like the total absence of clinical and radiological features of pneumonia. The premalignant change in the vulva was also unusual since vulval carcinoma has not been reported so far in children with this disorder. This child will require a close follow-up to look for malignant transformation.

Myristicin and phenytoin toxicity in an infant.

A developmentally normal infant presented with repeated episodes of afebrile status epilepticus following nutmeg ingestion. He had developed two episodes of afebrile status epilepticus and had received different treatments earlier, but the details of treatment were not available. On admission, he redeveloped convulsions and loading doses of phenytoin, phenobarbitone and midazolam were administered. However, seizures persisted and extrapyramidal movements, nystagmus and visual dysfunction were noted. Iatrogenic phenytoin toxicity was considered and confirmed by drug levels. His symptoms completely disappeared after discontinuation of phenytoin therapy. The initial seizures were attributed to myristicin, an active component of nutmeg, because of the temporal association. However, the subsequent seizures were due to phenytoin toxicity caused by administration of multiple loading doses. This case highlights that nutmeg, a spice, can cause serious toxic effects like status epilepticus. Furthermore, treatment of status epilepticus with phenytoin can cause iatrogenic seizures due to its narrow therapeutic range.

Encephalopathy in an infant with infantile spasms: possible role of valproate toxicity.

An infant presented with global developmental delay and infantile spasms. EEG was suggestive of hypsarrhythmia. She was started on sodium valproate, clonazepam and adrenocorticotropic hormone injection. After an initial improvement the child developed vomiting, altered sensorium and increase in frequency of seizures suggestive of encephalopathy. Valproate-induced hyperammonaemia or hepatic encephalopathy was considered and the drug was withheld following which there was a dramatic improvement. Paradoxically, the liver function tests and serum ammonia were normal. However, a complete reversal of encephalopathy, on withdrawal of the drug, strongly suggested an adverse drug reaction (ADR) due to valproic acid. Marginal elevation of serum valproic acid prompted us to use the Naranjo ADR probability score to confirm the diagnosis. This case highlights the fact that valproate toxicity can manifest with normal liver function and serum ammonia levels. This is the youngest reported case with this rare form of valproate-induced encephalopathy.

Posterior reversible encephalopathy syndrome unmasking acute glomerulonephritis.

Posterior reversible encephalopathy syndrome (PRES) is a recently described condition, wherein there is vasogenic oedema, seen on neuroimaging, predominantly over the parieto occipital regions of the cerebrum. Though, as the name implies, the condition is reversible, there may be fatalities and neurological sequelae. We are reporting a 9-year-old female child in whom the typical clinical and neurological findings of PRES were caused by an atypical presentation of acute glomerulonephritis.

DC8 and DC13 var genes associated with severe malaria bind avidly to diverse endothelial cells.

During blood stage infection, Plasmodium falciparum infected erythrocytes (IE) bind to host blood vessels. This virulence determinant enables parasites to evade spleen-dependent killing mechanisms, but paradoxically in some cases may reduce parasite fitness by killing the host. Adhesion of infected erythrocytes is mediated by P. falciparum erythrocyte membrane protein 1 (PfEMP1), a family of polymorphic adhesion proteins encoded by var genes. Whereas cerebral binding and severe malaria are associated with parasites expressing DC8 and DC13 var genes, relatively little is known about the non-brain endothelial selection on severe malaria adhesive types. In this study, we selected P. falciparum-IEs on diverse endothelial cell types and demonstrate that DC8 and DC13 var genes were consistently among the major var transcripts selected on non-brain endothelial cells (lung, heart, bone marrow). To investigate the molecular basis for this avid endothelial binding activity, recombinant proteins were expressed from the predominant upregulated DC8 transcript, IT4var19. In-depth binding comparisons revealed that multiple extracellular domains from this protein bound brain and non-brain endothelial cells, and individual domains largely did not discriminate between different endothelial cell types. Additionally, we found that recombinant DC8 and DC13 CIDR1 domains exhibited a widespread endothelial binding activity and could compete for DC8-IE binding to brain endothelial cells, suggesting they may bind the same host receptor. Our findings provide new insights into the interaction of severe malaria adhesive types and host blood vessels and support the hypothesis that parasites causing severe malaria express PfEMP1 variants with a superior ability to adhere to diverse endothelial cell types, and may therefore endow these parasites with a growth and transmission advantage.

Glycan masking of Plasmodium vivax Duffy Binding Protein for probing protein binding function and vaccine development.

Glycan masking is an emerging vaccine design strategy to focus antibody responses to specific epitopes, but it has mostly been evaluated on the already heavily glycosylated HIV gp120 envelope glycoprotein. Here this approach was used to investigate the binding interaction of Plasmodium vivax Duffy Binding Protein (PvDBP) and the Duffy Antigen Receptor for Chemokines (DARC) and to evaluate if glycan-masked PvDBPII immunogens would focus the antibody response on key interaction surfaces. Four variants of PVDBPII were generated and probed for function and immunogenicity. Whereas two PvDBPII glycosylation variants with increased glycan surface coverage distant from predicted interaction sites had equivalent binding activity to wild-type protein, one of them elicited slightly better DARC-binding-inhibitory activity than wild-type immunogen. Conversely, the addition of an N-glycosylation site adjacent to a predicted PvDBP interaction site both abolished its interaction with DARC and resulted in weaker inhibitory antibody responses. PvDBP is composed of three subdomains and is thought to function as a dimer; a meta-analysis of published PvDBP mutants and the new DBPII glycosylation variants indicates that critical DARC binding residues are concentrated at the dimer interface and along a relatively flat surface spanning portions of two subdomains. Our findings suggest that DARC-binding-inhibitory antibody epitope(s) lie close to the predicted DARC interaction site, and that addition of N-glycan sites distant from this site may augment inhibitory antibodies. Thus, glycan resurfacing is an attractive and feasible tool to investigate protein structure-function, and glycan-masked PvDBPII immunogens might contribute to P. vivax vaccine development.

Biotinidase deficiency--clinching the diagnosis rapidly can make all the difference!

A 2-month-old male infant, born of second degree consanguineous parentage, presented with seizures not responding to phenytoin and phenobarbitone. His perinatal period had been uneventful and there was no family history of seizures. On examination, he had failure to thrive, perioral and perianal rash, alopecia with hypopigmented hair, seborrhoeic dermatitis, bilateral blepharitis, respiratory distress and stridor. Neurological examination revealed hypertonia of all the four limbs, exaggerated deep tendon reflexes and papilloedema. Biotinidase deficiency was suspected within 24 h of admission and empiric oral biotin 10 mg twice daily was started. The symptoms, especially seizures, dramatically improved within 48 h. Serum biotinidase levels revealed a profound deficiency (0.10 nmol/min/ml serum) and the parents were advised regarding the need for regular biotin supplementation. The child is presently 10 months old, thriving well, developmentally normal and is seizure free with total resolution of skin and hair lesions.

Limb body wall complex in a still born fetus: a case report.

We report the case of a male, low birth weight, stillborn fetus of 36 weeks gestation with limb body wall complex. An interesting and rare feature noted in the propositus was the absence of the left subclavian artery and complete absence of the left upper limb. These findings seem to favor the vascular theory in the pathogenesis of this condition.

Snake bite mimicking brain death.

A 6 year old girl woke up with pain and increasing swelling over the left hand and difficulty in breathing. On examination, she had swelling of the left forearm and hand, flaccid quadriparesis and was in respiratory failure requiring mechanical ventilation. Two clean puncture wounds were identified on the left thumb. A provisional diagnosis of snake bite with severe envenomation was made and she was given anti snake venom therapy. Over a period of about 4 hours her weakness progressed. She became areflexic, developed internal and external ophthalmoplegia and loss of other brain stem reflexes mimicking brain death. Mechanical ventilation was continued despite features suggestive of brain stem dysfunction. About 36 hours after ventilation she showed a flicker of movement of her fingers and gradually the power improved. She was weaned off the ventilator and extubated after 5 days. External ophthalmoplegia is an established association with cobra envenomation, but, this combination of internal and external ophthalmoplegia can mimic brain death and pose a dilemma to the caregivers regarding continuation of therapy.

Swapping the substrate specificities of the neuropeptidases neurolysin and thimet oligopeptidase.

Thimet oligopeptidase (EC 3.4.24.15) and neurolysin (EC 3.4.24.16) are closely related zinc-dependent metallopeptidases that metabolize small bioactive peptides. They cleave many substrates at the same sites, but they recognize different positions on others, including neurotensin, a 13-residue peptide involved in modulation of dopaminergic circuits, pain perception, and thermoregulation. On the basis of crystal structures and previous mapping studies, four sites (Glu-469/Arg-470, Met-490/Arg-491, His-495/Asn-496, and Arg-498/Thr-499; thimet oligopeptidase residues listed first) in their substrate-binding channels appear positioned to account for differences in specificity. Thimet oligopeptidase mutated so that neurolysin residues are at all four positions cleaves neurotensin at the neurolysin site, and the reverse mutations in neurolysin switch hydrolysis to the thimet oligopeptidase site. Using a series of constructs mutated at just three of the sites, it was determined that mutations at only two (Glu-469/Arg-470 and Arg-498/Thr-499) are required to swap specificity, a result that was confirmed by testing the two-mutant constructs. If only either one of the two sites is mutated in thimet oligopeptidase, then the enzyme cleaves almost equally at the two hydrolysis positions. Crystal structures of both two-mutant constructs show that the mutations do not perturb local structure, but side chain conformations at the Arg-498/Thr-499 position differ from those of the mimicked enzyme. A model for differential recognition of neurotensin based on differences in surface charge distribution in the substrate binding sites is proposed. The model is supported by the finding that reducing the positive charge on the peptide results in cleavage at both hydrolysis sites.

Hypomelanosis of ito.

Four-year-old boy presented with hypopigmented skin lesions since birth and seizure of recent onset. He had psychomotor retardation and hemi hypertrophy of left half of body. Computerised tomography scan findings were suggestive of hemimegalencephaly. On clinical grounds, a diagnosis of Hypomelanosis of Ito was made.