A Case of a Serum Sickness-Like Reaction After Postexposure Rabies Prophylaxis.

BACKGROUND: Serum sickness secondary to rabies postexposure prophylaxis is not well documented in the medical literature. Our case describes serum sickness after exposure to human-derived rabies immunoglobulin (HRIG) and three human diploid rabies vaccines (HDCV) in a young adult male. CASE REPORT: A 30-year-old previously healthy male patient presented to the Emergency Department with complaints of fever, rash, and jaundice, and had a hospital course complicated by biliary stenosis likely secondary to reactive periportal lymphadenopathy. His initial laboratory values demonstrated obstructive jaundice and slightly elevated complement component 4 levels. These symptoms likely are due to the course of HRIG and HDCV vaccines the patient completed after being exposed to a rabies-positive bat in his home. The patient was hospitalized for 8 days, during which he underwent an endoscopic retrograde cholangiopancreatography with sphincterotomy and biliary stenting. He had one repeat hospitalization for acute blood loss anemia attributed to sphincterotomy, which did not require transfusion or further intervention. Liver biopsy showed cholestatic hepatitis. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Medical literature describing serum sickness or a serum sickness-like reaction occurring from exposure to HRIG or HDCV is sparse despite the commonality of postexposure rabies prophylaxis in health care. It is important to educate practitioners on this potential complication and highlight next potential consultations and treatments

C-Terminal Proline Deletions in KCNC3 Cause Delayed Channel Inactivation and an Adult-Onset Progressive SCA13 With Spasticity

Mutations in the potassium channel gene KCNC3 (Kv3.3) cause the autosomal dominant neurological disease, spinocerebellar ataxia 13 (SCA13). In this study, we expand the genotype-phenotype repertoire of SCA13 by describing the novel KCNC3 deletion p.Pro583_Pro585del highlighting the allelic heterogeneity observed in SCA13 patients. We characterize adult-onset, progressive clinical symptoms of two afflicted kindred and introduce the symptom of profound spasticity not previously associated with the SCA13 phenotype. We also present molecular and electrophysiological characterizations of the mutant protein in mammalian cell culture. Mechanistically, the p.Pro583_Pro585del protein showed normal membrane trafficking with an altered electrophysiological profile, including slower inactivation and decreased sensitivity to the inactivation-accelerating effects of the actin depolymerizer latrunculin B. Taken together, our results highlight the clinical importance of the intracellular C-terminal portion of Kv3.3 and its association with ion channel function

A <i>KCNC3</i> mutation causes a neurodevelopmental, non-progressive SCA13 subtype associated with dominant negative effects and aberrant EGFR trafficking

<div><p>The autosomal dominant spinocerebellar ataxias (SCAs) are a diverse group of neurological disorders anchored by the phenotypes of motor incoordination and cerebellar atrophy. Disease heterogeneity is appreciated through varying comorbidities: dysarthria, dysphagia, oculomotor and/or retinal abnormalities, motor neuron pathology, epilepsy, cognitive impairment, autonomic dysfunction, and psychiatric manifestations. Our study focuses on SCA13, which is caused by several allelic variants in the voltage-gated potassium channel KCNC3 (Kv3.3). We detail the clinical phenotype of four SCA13 kindreds that confirm causation of the <i>KCNC3</i>^<i>R423H</i> allele. The heralding features demonstrate congenital onset with non-progressive, neurodevelopmental cerebellar hypoplasia and lifetime improvement in motor and cognitive function that implicate compensatory neural mechanisms. Targeted expression of human KCNC3^R423H in <i>Drosophila</i> triggers aberrant wing veins, maldeveloped eyes, and fused ommatidia consistent with the neurodevelopmental presentation of patients. Furthermore, human KCNC3^R423H expression in mammalian cells results in altered glycosylation and aberrant retention of the channel in anterograde and/or endosomal vesicles. Confirmation of the absence of plasma membrane targeting was based on the loss of current conductance in cells expressing the mutant channel. Mechanistically, genetic studies in <i>Drosophila</i>, along with cellular and biophysical studies in mammalian systems, demonstrate the dominant negative effect exerted by the mutant on the wild-type (WT) protein, which explains dominant inheritance. We demonstrate that ocular co-expression of KCNC3^R423H with <i>Drosophila</i> epidermal growth factor receptor (dEgfr) results in striking rescue of the eye phenotype, whereas KCNC3^R423H expression in mammalian cells results in aberrant intracellular retention of human epidermal growth factor receptor (EGFR). Together, these results indicate that the neurodevelopmental consequences of KCNC3^R423H may be mediated through indirect effects on EGFR signaling in the developing cerebellum. Our results therefore confirm the <i>KCNC3</i>^<i>R423H</i> allele as causative for SCA13, through a dominant negative effect on KCNC3^WT and links with EGFR that account for dominant inheritance, congenital onset, and disease pathology.</p></div