Connexin32 and X-Linked Charcot-Marie-Tooth Disease

This paper deals with the genetic defect responsible for the X-linked form of Charcot-Marie-Tooth disease.Mutations in the gap junction geneconnexin32(Cx32) cause the X-linked form of Charcot–Marie–Tooth disease, an inherited demyelinating neuropathy

Effect of Hydrocortisone on Mortality and Organ Support in Patients With Severe COVID-19: The REMAP-CAP COVID-19 Corticosteroid Domain Randomized Clinical Trial.

Importance: Evidence regarding corticosteroid use for severe coronavirus disease 2019 (COVID-19) is limited. Objective: To determine whether hydrocortisone improves outcome for patients with severe COVID-19. Design, Setting, and Participants: An ongoing adaptive platform trial testing multiple interventions within multiple therapeutic domains, for example, antiviral agents, corticosteroids, or immunoglobulin. Between March 9 and June 17, 2020, 614 adult patients with suspected or confirmed COVID-19 were enrolled and randomized within at least 1 domain following admission to an intensive care unit (ICU) for respiratory or cardiovascular organ support at 121 sites in 8 countries. Of these, 403 were randomized to open-label interventions within the corticosteroid domain. The domain was halted after results from another trial were released. Follow-up ended August 12, 2020. Interventions: The corticosteroid domain randomized participants to a fixed 7-day course of intravenous hydrocortisone (50 mg or 100 mg every 6 hours) (n = 143), a shock-dependent course (50 mg every 6 hours when shock was clinically evident) (n = 152), or no hydrocortisone (n = 108). Main Outcomes and Measures: The primary end point was organ support-free days (days alive and free of ICU-based respiratory or cardiovascular support) within 21 days, where patients who died were assigned -1 day. The primary analysis was a bayesian cumulative logistic model that included all patients enrolled with severe COVID-19, adjusting for age, sex, site, region, time, assignment to interventions within other domains, and domain and intervention eligibility. Superiority was defined as the posterior probability of an odds ratio greater than 1 (threshold for trial conclusion of superiority >99%). Results: After excluding 19 participants who withdrew consent, there were 384 patients (mean age, 60 years; 29% female) randomized to the fixed-dose (n = 137), shock-dependent (n = 146), and no (n = 101) hydrocortisone groups; 379 (99%) completed the study and were included in the analysis. The mean age for the 3 groups ranged between 59.5 and 60.4 years; most patients were male (range, 70.6%-71.5%); mean body mass index ranged between 29.7 and 30.9; and patients receiving mechanical ventilation ranged between 50.0% and 63.5%. For the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively, the median organ support-free days were 0 (IQR, -1 to 15), 0 (IQR, -1 to 13), and 0 (-1 to 11) days (composed of 30%, 26%, and 33% mortality rates and 11.5, 9.5, and 6 median organ support-free days among survivors). The median adjusted odds ratio and bayesian probability of superiority were 1.43 (95% credible interval, 0.91-2.27) and 93% for fixed-dose hydrocortisone, respectively, and were 1.22 (95% credible interval, 0.76-1.94) and 80% for shock-dependent hydrocortisone compared with no hydrocortisone. Serious adverse events were reported in 4 (3%), 5 (3%), and 1 (1%) patients in the fixed-dose, shock-dependent, and no hydrocortisone groups, respectively. Conclusions and Relevance: Among patients with severe COVID-19, treatment with a 7-day fixed-dose course of hydrocortisone or shock-dependent dosing of hydrocortisone, compared with no hydrocortisone, resulted in 93% and 80% probabilities of superiority with regard to the odds of improvement in organ support-free days within 21 days. However, the trial was stopped early and no treatment strategy met prespecified criteria for statistical superiority, precluding definitive conclusions. Trial Registration: ClinicalTrials.gov Identifier: NCT02735707

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Connexin32 in peripheral nerve: Normal and disease states

Connexin32 (Cx32) is expressed by myelinating Schwann cells and localized principally to Schmidt-Lanterman incisures and paranodal regions, both regions of non-compact myelin. Sequence analysis revealed mutations in Cx32 associated with X-linked Charcot-Marie-Tooth disease (CMTX), a progressive, demyelinating peripheral neuropathy. Given this: what is the normal function of connexin32 in peripheral nerve, and how do mutations in this gene cause demyelination? To determine whether there are functional gap junctions in peripheral nerve, we injected dyes of differing molecular mass into myelinating Schwann cells of teased, living sciatic nerve fibers. Confocal analysis of injected fibers showed that 5,6-carboxyfluorescein (5,6-CF) (376 MW), but not larger dyes, passes through the incisures to the thin layer of cytoplasm adjacent to the axon (adaxonal cytoplasm). These results indicate that there is a radial pathway for diffusion of small molecules across the myelin sheath. Pre-incubating the teased fibers in agents known to uncouple gap junctions blocks the ability of 5,6-CF to diffuse into the adaxonal cytoplasm. This suggests that the radial pathway across the myelin sheath is dependent on functional gap junctions, such as formed by Cx32. To determine whether the presence of mutant protein is sufficient to cause a demyelinating neuropathy, we made transgenic mice expressing mutant (R142W) or wild type (WT) Cx32. The nerves of R142W transgenic lines had decreased levels of Cx32 on western blots, aberrant localization of the protein by immunohistochemistry, and progressive demyelination with age. Transgenic mice expressing the WT construct showed over-expression on western blots, normal localization at nodes and incisures by immunostaining, and split myelin sheaths. Thus, the R142W mutant protein has dominant effects that are distinct from overexpression, and the mutant protein likely interferes with the normal processing or trafficking of both mutant and wild type Cx32. Thus, we have developed mutant transgenic mice that are an animal model for CMTX, providing important insight into the disease mechanism. Both mutant and wild type transgenic mice will enable further investigation into the precise role of Cx32 in myelinating Schwann cells and basic biology of myelinating Schwann cells

Connexin32 in peripheral nerve: Normal and disease states

Connexin32 (Cx32) is expressed by myelinating Schwann cells and localized principally to Schmidt-Lanterman incisures and paranodal regions, both regions of non-compact myelin. Sequence analysis revealed mutations in Cx32 associated with X-linked Charcot-Marie-Tooth disease (CMTX), a progressive, demyelinating peripheral neuropathy. Given this: what is the normal function of connexin32 in peripheral nerve, and how do mutations in this gene cause demyelination? To determine whether there are functional gap junctions in peripheral nerve, we injected dyes of differing molecular mass into myelinating Schwann cells of teased, living sciatic nerve fibers. Confocal analysis of injected fibers showed that 5,6-carboxyfluorescein (5,6-CF) (376 MW), but not larger dyes, passes through the incisures to the thin layer of cytoplasm adjacent to the axon (adaxonal cytoplasm). These results indicate that there is a radial pathway for diffusion of small molecules across the myelin sheath. Pre-incubating the teased fibers in agents known to uncouple gap junctions blocks the ability of 5,6-CF to diffuse into the adaxonal cytoplasm. This suggests that the radial pathway across the myelin sheath is dependent on functional gap junctions, such as formed by Cx32. To determine whether the presence of mutant protein is sufficient to cause a demyelinating neuropathy, we made transgenic mice expressing mutant (R142W) or wild type (WT) Cx32. The nerves of R142W transgenic lines had decreased levels of Cx32 on western blots, aberrant localization of the protein by immunohistochemistry, and progressive demyelination with age. Transgenic mice expressing the WT construct showed over-expression on western blots, normal localization at nodes and incisures by immunostaining, and split myelin sheaths. Thus, the R142W mutant protein has dominant effects that are distinct from overexpression, and the mutant protein likely interferes with the normal processing or trafficking of both mutant and wild type Cx32. Thus, we have developed mutant transgenic mice that are an animal model for CMTX, providing important insight into the disease mechanism. Both mutant and wild type transgenic mice will enable further investigation into the precise role of Cx32 in myelinating Schwann cells and basic biology of myelinating Schwann cells

Haploinsufficiency and triploinsensitivity of the same 6p25.1p24.3 region in a family

BACKGROUND: Chromosome 6pter-p24 deletion syndrome (OMIM #612582) is a recognized chromosomal disorder. Most of the individuals with this syndrome carry a terminal deletion of the short arm of chromosome 6 (6p) with a breakpoint within the 6p25.3p23 region. An approximately 2.1 Mb terminal region has been reported to be responsible for some major features of the syndrome. The phenotypic contributions of other deleted regions are unknown. Interstitial deletions of the region are uncommon, and reciprocal interstitial duplication in this region is extremely rare. CASE PRESENTATION: We present a family carrying an interstitial deletion and its reciprocal duplication within the 6p25.1p24.3 region. The deletion is 5.6 Mb in size and was detected by array comparative genomic hybridization (aCGH) in a 26-month-old female proband who presented speech delay and mild growth delay, bilateral conductive hearing loss and dysmorphic features. Array CGH studies of her family members detected an apparently mosaic deletion of the same region in the proband’s mildly affected mother, but a reciprocal interstitial duplication in her phenotypically normal brother. Further chromosomal and fluorescence in situ hybridization (FISH) analyses revealed that instead of a simple mosaic deletion of 6p25.1p24.3, the mother actually carries three cell populations in her peripheral blood, including a deletion (~70 %), a duplication (~8 %) and a normal (~22 %) populations. Therefore, both the deletion and duplication seen in the siblings were apparently inherited from the mother. CONCLUSIONS: Interstitial deletion within the 6p25.1p24.3 region and its reciprocal duplication may co-exist in the same individual and/or family due to mitotic unequal sister chromatid exchange. While the deletion causes phenotypes reportedly associated with the chromosome 6pter-p24 deletion syndrome, the reciprocal duplication may have no or minimal phenotypic effect, suggesting possible triploinsensitivity of the same region. In addition, the cells with the duplication may compensate the phenotypic effect of the cells with the deletion in the same individual as implied by the maternal karyotype and her mild phenotype. Chromosomal and FISH analyses are essential to verify abnormal cytogenomic array findings

Connexin32 and X-linked Charcot–Marie–Tooth Disease

Mutations in the gap junction geneconnexin32(Cx32) cause the X-linked form of Charcot–Marie–Tooth disease, an inherited demyelinating neuropathy. More than 130 different mutations have been described, affecting all portions of the Cx32 protein. In transfected cells, the mutant Cx32 proteins encoded by someCx32mutations fail to reach the cell surface; other mutant proteins reach the cell surface, but only one of these forms functional gap junctions. In peripheral nerve, Cx32 is localized to incisures and paranodes, regions of noncompact myelin within the myelin sheath. This localization suggests that Cx32 forms “reflexive” gap junctions that allow ions and small molecules to diffuse directly across the myelin sheath, which is a thousandfold shorter distance than the circumferential pathway through the Schwann cell cytoplasm.Cx32mutations may interrupt this shorter pathway or have other toxic effects, thereby injuring myelinating Schwann cells and their axons

Connexin32 and X-Linked Charcot-Marie-Tooth Disease

This paper deals with the genetic defect responsible for the X-linked form of Charcot-Marie-Tooth disease.Mutations in the gap junction geneconnexin32(Cx32) cause the X-linked form of Charcot–Marie–Tooth disease, an inherited demyelinating neuropathy

Challenges and disparities in the application of personalized genomic medicine to populations with African ancestry

To characterize the extent and impact of ancestry-related biases in precision genomic medicine, we use 642 whole-genome sequences from the Consortium on Asthma among African-ancestry Populations in the Americas (CAAPA) project to evaluate typical filters and databases. We find significant correlations between estimated African ancestry proportions and the number of variants per individual in all variant classification sets but one. The source of these correlations is highlighted in more detail by looking at the interaction between filtering criteria and the ClinVar and Human Gene Mutation databases. ClinVar\u27s correlation, representing African ancestry-related bias, has changed over time amidst monthly updates, with the most extreme switch happening between March and April of 2014 (r=0.733 to r=-0.683). We identify 68 SNPs as the major drivers of this change in correlation. As long as ancestry-related bias when using these clinical databases is minimally recognized, the genetics community will face challenges with implementation, interpretation and cost-effectiveness when treating minority populations