Background Life-threatening disorders of heart rhythm may arise during infancy and can result in the sudden and tragic death of a child. We performed exome sequencing on two unrelated infants presenting with recurrent cardiac arrest to discover a genetic cause. Methods and Results We ascertained two unrelated infants (probands) with recurrent cardiac arrest and dramatically prolonged QTc interval who were both born to healthy parents. The two parent-child trios were investigated using exome sequencing to search for de novo genetic variants. We then performed follow-up candidate gene screening on an independent cohort of 82 subjects with congenital long-QT syndrome without an identified genetic cause. Biochemical studies were performed to determine the functional consequences of mutations discovered in two genes encoding calmodulin. We discovered three heterozygous de novo mutations in either CALM1 or CALM2, two of the three human genes encoding calmodulin, in the two probands and in two additional subjects with recurrent cardiac arrest. All mutation carriers were infants who exhibited life-threatening ventricular arrhythmias combined variably with epilepsy and delayed neurodevelopment. Mutations altered residues in or adjacent to critical calcium binding loops in the calmodulin carboxyl-terminal domain. Recombinant mutant calmodulins exhibited several fold reductions in calcium binding affinity. Conclusions Human calmodulin mutations disrupt calcium ion binding to the protein and are associated with a life-threatening condition in early infancy. Defects in calmodulin function will disrupt important calcium signaling events in heart affecting membrane ion channels, a plausible molecular mechanism for potentially deadly disturbances in heart rhythm during infancy.

Myositis ossificans is a self-limiting, benign ossifying lesion that can affect any type of soft tissue, including subcutaneous fat, tendons, and nerves. It is most commonly found in muscle as a solitary lesion. Ossifying soft-tissue lesions historically have been inconsistently classified. Fundamentally, myositis ossificans can be categorized into nonhereditary and hereditary types, with the latter being a distinct entity with a separate pathophysiology and treatment approach. The etiology of myositis ossificans is variable; however, clinical presentation generally is characterized by an ossifying soft-tissue mass. Advanced cross-sectional imaging alone can be nonspecific and may appear to be similar to more sinister etiologies. Therefore, the evaluation of a suspicious soft-tissue mass often necessitates multiple imaging modalities for accurate diagnosis. When imaging is indeterminate, biopsy may be required for a histologic diagnosis. However, histopathology varies based on stage of evolution. The treatment of myositis ossificans is complex and is often made in a multidisciplinary fashion because accurate diagnosis is fundamental to a successful outcome.

Selective degradation of proteins by proteolysis targeting chimeras (PROTACs) offers a promising potential alternative to protein inhibition for therapeutic intervention. Current PROTAC molecules incorporate a ligand for the target protein, a linker, and an E3 ubiquitin ligase recruiting group, which bring together target protein and ubiquitinating machinery. Such hetero-bifunctional molecules require significant linker optimization and possess high molecular weight, which can limit cellular permeation, solubility, and other drug-like properties. We show here that the hetero-bifunctional molecule can be formed intracellularly by bio-orthogonal click combination of two smaller precursors. We designed a tetrazine tagged thalidomide derivative which reacts rapidly with a trans-cyclo-octene tagged ligand of the target protein in cells to form a cereblon E3 ligase recruiting PROTAC molecule. The in-cell click-formed proteolysis targeting chimeras (CLIPTACs) were successfully used to degrade two key oncology targets, BRD4 and ERK1/2. ERK1/2 degradation was achieved using a CLIPTAC based on a covalent inhibitor. We expect this approach to be readily extendable to other inhibitor-protein systems because the tagged E3 ligase recruiter is capable of undergoing the click reaction with a suitably tagged ligand of any protein of interest to elicit its degradation.

Rationale Calmodulin (CaM) mutations are associated with an autosomal-dominant syndrome of ventricular arrhythmia and sudden death that can present with divergent clinical features of catecholaminergic polymorphic ventricular tachycardia (CPVT)or long QT syndrome (LQTS).CaM binds to and inhibits RyR2 Ca release channels in the heart, but whether arrhythmogenic CaM mutants alter RyR2 function is not known. Objective To gain mechanistic insight into how human CaM mutations affect RyR2 Ca channels. Methods and Results We studied recombinant CaM mutants associated with CPVT (N54I, N98S) or LQTS (D96V, D130G, F142L). As a group, all LQTS-associated CaM mutants(LQTS-CaMs) exhibited reduced Ca affinity, whereas CPVT-associated CaM mutants(CPVT-CaMs) had either normal or modestly lower Ca affinity. In permeabilized ventricular myocytes, CPVT-CaMs at a physiological intracellular concentration (100nM) promoted significantly higher spontaneous Ca wave and spark activity, a typical cellular phenotype of CPVT. Compared to wild-type (WT) CaM, CPVT-CaMs caused greater RyR2 single channel open probability and showed enhanced binding affinity to RyR2. Even a 1:8 mixture of CPVT-CaM:WT-CaM activated Ca waves, demonstrating functional dominance. By contrast, LQTS-CaMs did not promote Ca waves and exhibited either normal regulation of RyR2 single channels (D96V) or lower RyR2 binding affinity (D130G, F142L). None of the CaM mutants altered Ca/CaM binding to CaM-kinase II. Conclusions A small proportion of CPVT-CaM is sufficient to evoke arrhythmogenic Ca disturbances, whereas LQTS-CaMs do not. Our findings explain the clinical presentation and autosomal dominant inheritance of CPVT-CaM mutations and suggest that RyR2-interactions are unlikely to explain arrhythmogenicity of LQTS-CaM mutations.