Translational insights and overall survival in the U31402-A-U102 study of patritumab deruxtecan (HER3-DXd) in EGFR-mutated NSCLC.

BACKGROUND: Human epidermal growth factor receptor 3 (HER3) is broadly expressed in non-small-cell lung cancer (NSCLC) and is the target of patritumab deruxtecan (HER3-DXd), an antibody-drug conjugate consisting of a HER3 antibody attached to a topoisomerase I inhibitor payload via a tetrapeptide-based cleavable linker. U31402-A-U102 is an ongoing phase I study of HER3-DXd in patients with advanced NSCLC. Patients with epidermal growth factor receptor (EGFR)-mutated NSCLC that progressed after EGFR tyrosine kinase inhibitor (TKI) and platinum-based chemotherapy (PBC) who received HER3-DXd 5.6 mg/kg intravenously once every 3 weeks had a confirmed objective response rate (cORR) of 39%. We present median overall survival (OS) with extended follow-up in a larger population of patients with EGFR-mutated NSCLC and an exploratory analysis in those with acquired genomic alterations potentially associated with resistance to HER3-DXd. PATIENTS AND METHODS: Safety was assessed in patients with EGFR-mutated NSCLC previously treated with EGFR TKI who received HER3-DXd 5.6 mg/kg; efficacy was assessed in those who also had prior PBC. RESULTS: In the safety population (N = 102), median treatment duration was 5.5 (range 0.7-27.5) months. Grade ≥3 adverse events occurred in 76.5% of patients; the overall safety profile was consistent with previous reports. In 78/102 patients who had prior third-generation EGFR TKI and PBC, cORR by blinded independent central review (as per RECIST v1.1) was 41.0% [95% confidence interval (CI) 30.0% to 52.7%], median progression-free survival was 6.4 (95% CI 4.4-10.8) months, and median OS was 16.2 (95% CI 11.2-21.9) months. Patients had diverse mechanisms of EGFR TKI resistance at baseline. At tumor progression, acquired mutations in ERBB3 and TOP1 that might confer resistance to HER3-DXd were identified. CONCLUSIONS: In patients with EGFR-mutated NSCLC after EGFR TKI and PBC, HER3-DXd treatment was associated with a clinically meaningful OS. The tumor biomarker characterization comprised the first description of potential mechanisms of resistance to HER3-DXd therapy.

Congenital myasthenic syndrome by mutation of the ColQ gene: Phenotypic and evolutionary profile of three Algerian families.

BACKGROUND: Congenital myasthenic syndromes (CMS) are rare genetic neuromuscular disorders. The COLQ gene encoding the collagenous subunit of the acetyl cholinesterase enzyme tail is implicated in a synaptic form of CMS (also called type 5, according to the new gene table 2020 classification). OBJECTIVE: To study the clinical phenotype of three families with COLQ gene mutations. METHODS: We report a series of three consanguineous families, with seven affected patients, carrying three different mutations of the COLQ gene, one of which has never been reported in the literature before. RESULTS: We studied their clinical and paraclinical phenotypes, and try to compare the three families as well as compare them with other series carrying COLQ gene mutations reported in the literature. CONCLUSION: COLQ gene mutations have phenotypic particularities that must be recognized to propose appropriate genetic study.

Efficacy and safety of midostaurin in patients with advanced systemic mastocytosis: 10-year median follow-up of a phase II trial.

Patients with advanced systemic mastocytosis (SM) (e.g. aggressive SM (ASM), SM with an associated hematologic neoplasm (SM-AHN) and mast cell leukemia (MCL)) have limited treatment options and exhibit reduced survival. Midostaurin is an oral multikinase inhibitor that inhibits D816V-mutated KIT, a primary driver of SM pathogenesis. We conducted a phase II trial of midostaurin 100 mg twice daily, administered as 28-day cycles, in 26 patients (ASM, n=3; SM-AHN, n= 17; MCL, n=6) with at least one sign of organ damage. During the first 12 cycles, the overall response rate was 69% (major/partial response: 50/19%) with clinical benefit in all advanced SM variants. With ongoing therapy, 2 patients achieved a complete remission of their SM. Midostaurin produced a ⩾50% reduction in bone marrow mast cell burden and serum tryptase level in 68% and 46% of patients, respectively. Median overall survival for the entire cohort was 40 months, and 18.5 months for MCL patients. Low-grade gastrointestinal side effects were common and manageable with antiemetics. The most frequent grade 3/4 nonhematologic and hematologic toxicities were asymptomatic hyperlipasemia (15%) and anemia (12%). With median follow-up of 10 years, no unexpected toxicities emerged. These data establish the durable activity and tolerability of midostaurin in advanced SM.

Heterozygous CLCN1 mutations can modulate phenotype in sodium channel myotonia.

Nondystrophic myotonias are characterized by muscle stiffness triggered by voluntary movement. They are caused by mutations in either the CLCN1 gene in myotonia congenita or in the SCN4A gene in paramyotonia congenita and sodium channel myotonias. Clinical and electrophysiological phenotypes of these disorders have been well described. No concomitant mutations in both genes have been reported yet. We report five patients from three families showing myotonia with both chloride and sodium channel mutations. Their clinical and electrophysiological phenotypes did not fit with the phenotype known to be associated with the mutation initially found in SCN4A gene, which led us to screen and find an additional mutation in CLCN1 gene. Our electrophysiological and clinical observations suggest that heterozygous CLCN1 mutations can modify the clinical and electrophysiological expression of SCN4A mutation.

[Congenital myasthenic syndromes: difficulties in the diagnosis, course and prognosis, and therapy--The French National Congenital Myasthenic Syndrome Network experience]. / Syndromes myasthéniques congénitaux: difficultés diagnostiques, évolution et pronostic, thérapeutique--l'expérience du réseau national "Syndromes Myasthéniques Congénitaux".

Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders caused by genetic defects affecting neuromuscular transmission and leading to muscle weakness accentuated by exertion. Three different aspects have been investigated by members of the national French CMS Network: the difficulties in making a proper diagnosis; the course and long-term prognosis; and the response to therapy, especially for CMS that do not respond to cholinesterase inhibitors. CMS diagnosis is late in most cases because of confusion with other entities such as: congenital myopathies, due to the frequent presentation in patients of myopathies such as permanent muscle weakness, atrophy and scoliosis, and the abnormalities of internal structure, diameter and distribution of fibers (type I predominance, type II atrophy) seen on biopsy; seronegative autoimmune myasthenia gravis, when CMS is of late onset; and metabolic myopathy, with the presence of lipidosis in muscle. The long-term prognosis of CMS was studied in a series of 79 patients recruited with the following gene mutations: CHRNA; CHRNE; DOK7; COLQ; RAPSN; AGRN; and MUSK. Disease-course patterns (progressive worsening, exacerbation, stability, improvement) could be variable throughout life in a given patient. DOK7 patients had the most severe disease course with progressive worsening: of the eight wheelchair-bound and ventilated patients, six had mutations of this gene. Pregnancy was a frequent cause of exacerbation. Anticholinesterase agents are the first-line therapy for CMS patients, except for cases of slow-channel CMS, COLQ and DOK7. In our experience, 3,4-DAP was a useful complement for several patients harboring CMS with AChR loss or RAPSN gene mutations. Ephedrine was given to 18 patients (eight DOK7, five COLQ, four AGRN and one RAPSN). Tolerability was good. Therapeutic responses were encouraging even in the most severely affected patients, particularly with DOK7 and COLQ. Salbutamol was a good alternative in one patient who was allergic to ephedrine.

Pregnancy in congenital myasthenic syndrome.

Some case reports have suggested possible worsening of the clinical condition of patients with congenital myasthenic syndromes (CMS) during pregnancy. However, this risk has not yet been quantified in a significant number of patients. Using a standardized report form, we reviewed the gynecological and obstetrical medical history of all patients with CMS listed in the French Registry. The data were reviewed with the assistance of the patients to insure accuracy. We report on 17 pregnancies in eight patients with CMS with mutations in CHRNA1, CHRNE, CHRND, GFPT1, COLQ, or DOK7. Symptoms worsened for six patients during at least one of their pregnancies, and one patient required hospitalization in an intensive care unit during the post-partum period. One patient never recovered to the level of her pre-pregnancy clinical condition. Only one caesarean section was performed. The outcome for children was excellent, with the exceptions of a pulmonary artery atresia in the offspring of a mother on pyridostigmin and a newborn with a severe neonatal congenital myasthenic syndrome (an autosomic dominant slow channel transmission). Our study argues in favor of frequent clinical worsening of symptoms during pregnancy in patients with CMS. These patients should be closely followed by neurologists during the course of pregnancy. However, the overall clinical prognosis is good since the vast majority of patients recovered their pre-pregnancy clinical status six months after the delivery.

Long-term follow-up of patients with congenital myasthenic syndrome caused by COLQ mutations.

Congenital myasthenic syndromes (CMS) are clinically and genetically heterogeneous inherited disorders characterized by impaired neuromuscular transmission. Mutations in the acetylcholinesterase (AChE) collagen-like tail subunit gene (COlQ) cause recessive forms of synaptic CMS with end plate AChE deficiency. We present data on 15 COLQ -mutant CMS carrying 16 different mutations (9 novel ones identified) followed-up for an average period of 10 ears. The mean age at the first examination was 19 ears old (range from 3 to 48). We report relapses during short or long-term periods characterized by worsening of muscle weakness sometimes associated with respiratory crises. All the relapses ended spontaneously or with 3-4 DAP or ephedrine with no residual impairment. The triggering factors identified were esterase inhibitors, effort, puberty or pregnancy highlighting the importance of hormonal factors. There was no genotype-phenotype correlation. At the end of the follow-up, 80% of patients were ambulant and 87% of patients had no respiratory trouble in spite of severe relapses.

Acamprosate modulates experimental autoimmune encephalomyelitis.

OBJECTIVE: This pilot study aimed to determine the efficacy of acamprosate (N-acetyl homotaurine) in reducing the pathological features of experimental autoimmune encephalomyelitis (EAE) which is an animal model for multiple sclerosis (MS). BACKGROUND: The amino acid taurine has multiple biological activities including immunomodulation and neuromodulation. The synthetic acetylated taurine derivative, acamprosate, which crosses the blood-brain barrier more readily compared to taurine, is currently being used for the prevention of alcohol withdrawal symptoms associated with enhanced glutamatergic receptor function and GABA receptor hypofunction. METHODS: EAE was induced in C57BL/6 female mice with myelin oligodendrocyte glyocoprotein, amino acid 35-55. Mice were treated with 20, 100 and 500 mg/kg acamprosate for 21 days. RESULTS: Neurological scores at disease peak were reduced by 21, 64 and 9% in the 20, 100 and 500 mg/kg groups, respectively. Neurological improvement in the 100 mg/kg group correlated with a reduction in numbers of inflammatory lesions and the extent of CNS demyelination. Blood TNF-α levels were significantly reduced in the 500 mg/kg group. DISCUSSION: Acamprosate and other taurine analogs have a potential for future MS therapy.

Severe neonatal episodic laryngospasm due to de novo SCN4A mutations: a new treatable disorder.

BACKGROUND: Myotonia is unusual in infants, and not well-known. METHODS: We describe neonatal life-threatening features of myotonia caused by de novo mutations in the muscle sodium channel gene SCN4A. RESULTS: Three male neonates initially displayed episodic laryngospasms, with face and limb myotonia appearing later. We found SCN4A de novo mutations in these neonates: p.Gly1306Glu in 2 unrelated cases and a novel mutation p.Ala799Ser in the third. Two patients survived their respiratory attacks and were efficiently treated by sodium channel blockers (mexiletine, carbamazepine) following diagnosis of myotonia. CONCLUSION: Severe neonatal episodic laryngospasm is a new phenotype caused by a sodium channelopathy, which can be alleviated by channel blockers.

Phenotype genotype analysis in 15 patients presenting a congenital myasthenic syndrome due to mutations in DOK7.

Congenital myasthenic syndromes (CMSs) are a heterogeneous group of diseases caused by genetic defects affecting neuromuscular transmission. Mutations of DOK7 have recently been described in recessive forms of CMS. Dok-7 is a cytoplasmic post-synaptic protein co-activator of the muscle-specific receptor-tyrosine kinase (MuSK) involved in neuromuscular synaptogenesis and maintenance. We report clinical, morphological and molecular data on 15 patients with mutations in DOK7. Eleven different mutations (5 novel) were identified and all patients but one were found to carry at least the common c.1124_1127dupTGCC mutation. Patients with DOK7 mutations have a particular limb-girdle pattern, without tubular aggregates but a frequent lipidosis on the muscle biopsy. Changes in pre- and post-synaptic compartments of the neuromuscular junction were also observed in muscle biopsies: terminal axons showed defective branching which resulted in a unique terminal axon contacting en passant postsynaptic cups. Clinical features, muscle biopsy findings or response to therapy were confusing in several patients. Characterization of this distinct phenotype is essential to provide clues for targeted genetic screening and to predict the therapeutic response to anticholinesterase treatments or ephedrine as has been suggested.

The non-dystrophic myotonias: molecular pathogenesis, diagnosis and treatment.

The non-dystrophic myotonias are an important group of skeletal muscle channelopathies electrophysiologically characterized by altered membrane excitability. Many distinct clinical phenotypes are now recognized and range in severity from severe neonatal myotonia with respiratory compromise through to milder late-onset myotonic muscle stiffness. Specific genetic mutations in the major skeletal muscle voltage gated chloride channel gene and in the voltage gated sodium channel gene are causative in most patients. Recent work has allowed more precise correlations between the genotype and the electrophysiological and clinical phenotype. The majority of patients with myotonia have either a primary or secondary loss of membrane chloride conductance predicted to result in reduction of the resting membrane potential. Causative mutations in the sodium channel gene result in an abnormal gain of sodium channel function that may show marked temperature dependence. Despite significant advances in the clinical, genetic and molecular pathophysiological understanding of these disorders, which we review here, there are important unresolved issues we address: (i) recent work suggests that specialized clinical neurophysiology can identify channel specific patterns and aid genetic diagnosis in many cases however, it is not yet clear if such techniques can be refined to predict the causative gene in all cases or even predict the precise genotype; (ii) although clinical experience indicates these patients can have significant progressive morbidity, the detailed natural history and determinants of morbidity have not been specifically studied in a prospective fashion; (iii) some patients develop myopathy, but its frequency, severity and possible response to treatment remains undetermined, furthermore, the pathophysiogical link between ion channel dysfunction and muscle degeneration is unknown; (iv) there is currently insufficient clinical trial evidence to recommend a standard treatment. Limited data suggest that sodium channel blocking agents have some efficacy. However, establishing the effectiveness of a therapy requires completion of multi-centre randomized controlled trials employing accurate outcome measures including reliable quantitation of myotonia. More specific pharmacological approaches are required and could include those which might preferentially reduce persistent muscle sodium currents or enhance the conductance of mutant chloride channels. Alternative strategies may be directed at preventing premature mutant channel degradation or correcting the mis-targeting of the mutant channels.

Relief from episodic weakness with pyridostigmine in paramyotonia congenita: a family study.

Pyridostigmine relieved episodic weakness in a family with paramyotonia congenita resulting from the R1448C mutation in the sodium channel gene. The transmission was autosomal dominant and the patients had paradoxical myotonia and exercise-induced weakness. On electrophysiological studies there were myotonic potentials, and there was progressive reduction of compound muscle action potential (CMAP) amplitudes after short exercise associated with clinical weakness. Pyridostigmine in doses of 60 mg three times daily abolished the drop in the postexercise CMAP amplitude and reduced the amplitude decrement to slow rate repetitive stimulation, but there continued to be a drop in amplitude on exposure to cold. The decline of the CMAP amplitude on exposure to cold was controlled by treatment with phenytoin. The clinical and electrophysiological features are discussed in relation to therapy with pyridostigmine and phenytoin.

Mechanisms underlying Andersen's syndrome pathology in skeletal muscle are revealed in human myotubes.

Andersen's syndrome is a rare disorder that has been defined with a triad: periodic paralysis, cardiac arrhythmia, and development anomalies. Muscle weakness has been reported in two-thirds of the patients. KCNJ2 remains the only gene linked to Andersen's syndrome; this gene encodes for the alpha-subunit of the strong inward-rectifier K+ channel Kir2.1. Several studies have shown that Andersen's syndrome mutations lead to a loss of function of the K+ channel activity in vitro. However, ex vivo studies on isolated patient muscle tissue have not been reported. We have performed muscle biopsies of controls and patients presenting with clinically and genetically defined Andersen's syndrome disorder. Myoblasts were cultured and characterized morphologically and functionally using the whole cell patch-clamp technique. No morphological difference was observed between Andersen's syndrome and control myoblasts at each passage of the cell culture. Cellular proliferation and viability were quantified in parallel with direct cell counts and showed no difference between control and Andersen's syndrome patients. Moreover, our data show no significant difference in myoblast fusion index among Andersen's syndrome and control patients. Current recordings carried out on myotubes revealed the absence of an inwardly rectifying Ba2+-sensitive current in affected patient cells. One consequence of the Ik1 current loss in Andersen's syndrome myotubes is a shift of the resting membrane potential toward depolarizing potentials. Our data describe for the first time the functional consequences of Andersen's syndrome mutations ex vivo and provide clues to the K+ channel pathophysiology in skeletal muscle.

[Misdiagnosis of mitochondrial myopathies: a study of 12 thymectomized patients]. / Errance diagnostique dans les myopathies mitochondriales: étude de 12 patients thymectomisés.

INTRODUCTION: Myasthenia gravis and mitochondrial myopathies have common symptoms (fatigability, ophthalmoplegia) that could lead to diagnosis confusion. METHODS: We systematically reviewed medical history and ancillary investigations regarding 12 patients (7F/5M, mean age 47+/-14 years) having a mitochondrial myopathy but who were previously misdiagnosed as autoimmune myasthenia gravis and in whom a thymectomy was performed. RESULTS: Ocular palsy, ptosis and bulbar palsy were present in all patients. Limb fatigability was present in 9 cases. Symptoms were fluctuant but without remission. The misdiagnosis of myasthenia was based on the following arguments: 1) decremental EMG response (2 cases); 2) positive injectable anticholinesterase drugs test (3 cases); 3) partial response to oral anticholinesterase medications (2 cases); 4) AChR antibodies titer of 0.6 nM considered as positive (1 case). A multisystemic involvement was present in 5 patients: peripheral neuropathy (2 cases), deafness (2 cases), cardiopathy (3 cases), cerebellar involvement (2 cases) and myoclonia (1 case). The diagnosis of mitochondrial myopathy (at a mean age of 38+/-12 years) has been certified on the results of muscle biopsy showing mitochondrial proliferation (12 cases) and deleted mitochondrial DNA (8 cases). CONCLUSIONS: In a patient presenting with oculomotor symptoms and muscle fatigability, progressive course and multisystemic involvement are major arguments for a mitochondrial myopathy. In the absence of relevant criteria arguing for Myasthenia Gravis (significant variability of muscle weakness, positive titer of anti-AChR or anti-MuSK antibodies, decremental EMG response), a muscle biopsy is required before indication of thymectomy to exclude a mitochondrial disease.

A new case of autosomal dominant myotonia associated with the V1589M missense mutation in the muscle sodium channel gene and its phenotypic classification.

We report a phenotype associated with the Val1589Met substitution in SCN4A gene in a French family which would be better classified as paramyotonia congenita. The proband was a 48-year-old woman, who described muscle stiffness and occasional flaccid weakness, both symptoms being induced by exercise, cold and heat. Severe muscle stiffness affected facial, oropharyngeal and limb muscles leading to transient paralysis of these muscles. One sister, two nephews and the son of the proband had similar symptoms. Molecular analysis of the muscle sodium channel gene (SCN4A) by nucleotide sequencing revealed a G-to-A transition of cDNA nucleotide at position 4765 predicting a substitution of methionine for valine at position 1589. This shows that the Val1589Met mutation in the SCN4 gene may cause different phenotypes, either potassium-aggravated myotonia or paramyotonia congenita. Familial or individual factors other than the missense mutation per se influence the expression of the disease in sodium channel disorders.

Human skeletal muscle sodium channelopathies.

Ion channels are transmembrane proteins that allow ions to flow in or out of the cell. Sodium and potassium channel activation and inactivation are the basis of action potential's production and conduction. During the past 15 years, ion channels have been implicated in diseases that have come to be known as the channelopathies. Over 30 mutations of the muscle channel gene SCN4A, which encodes the muscle voltage-gated sodium channel, have been described and associated with neuromuscular disorders like hypo- and hyper-kalaemic periodic paralyses (hypoPP and hyperPP), paramyotonia congenita, sodium channel myotonias and congenital myasthenic syndrome. Different mutations within the same gene (SCN4A) cause distinct clinical disorders, while mutations in different channel genes may result in similar phenotypes. In addition, identical sodium channel mutations can result in different clinical phenotypes (hyperPP or paramyotonia) in different members of the same family, suggesting that the genetic background and perhaps other epigenetic factors may influence the clinical expression of a particular mutation. This article reviews the clinical features of the skeletal muscle sodium channel diseases and highlights the phenotypic or genetic overlap in these disorders.

KIAA1509 is a novel PDGFRB fusion partner in imatinib-responsive myeloproliferative disease associated with a t(5;14)(q33;q32).

We report the cloning of a novel PDGFRB fusion gene partner in a patient with a chronic myeloproliferative disorder characterized by t(5;14)(q33;q32), who responded to treatment with imatinib mesylate. Fluorescence in situ hybridization demonstrated that PDGFRB was involved in the translocation. Long distance inversion PCR identified KIAA1509 as the PDGFRB fusion partner. KIAA1509 is an uncharacterized gene with a predicted coiled-coil oligomerization domain with homology to the HOOK family of proteins. The predicted KIAA1509-PDGFRbeta fusion protein contains the KIAA1509 coiled-coil domain fused to the cytoplasmic domain of PDGFRbeta that includes the tyrosine kinase domain. Imatinib therapy resulted in rapid normalization of the patient's blood counts, and subsequent bone marrow biopsies and karyotypic analysis were consistent with sustained complete remission.