Reinfection with SARS-CoV-2 in solid-organ transplant recipients: Incidence density and convalescent immunity prior to reinfection

BACKGROUND

Long-term protective immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains poorly characterized, particularly in solid organ transplant (SOT) patients.

METHOD

We determined the incidence density of SARS-CoV-2 reinfection in a cohort of adult SOT recipients initially infected between March 1st, 2020 and March 30th, 2021 and included those with initial infection before or after transplantation. Incidence density was the total cases divided by total days after initial diagnosis with active graft.

RESULTS

Of 210 infected recipients, five (2.4%) developed reinfection, including two who had received full mRNA vaccination, but none developed hypoxia. The incidence density for reinfection was 9.4 (95% confidence interval [CI] 3.9-22.6) and for primary infection the density was 9.1 (95% CI 7.9-10.5) cases/100,000 patient days. Two recipients had immunity evaluated in the weeks prior to reinfection, by measuring immunoglobulin-G (IgG) antibody titer to the SARS-CoV-2 receptor binding domain and virus-specific CD4+ and CD8+ T-cell reactivity following stimulation with SARS-CoV-2 peptide pools. Both mounted virus specific CD4 T-cell responses prior to reinfection (1.19% and 0.28% of total CD4 T cells) and both had reactive IgG testing (1.30 and 4.99 signal/cut off ratio).

CONCLUSIONS

This suggests that SOT recipients infected with SARS-CoV-2 remain at high risk for reinfection even after generating cellular and humoral immune responses.

Biallelic mutations in sord are a common cause of potentially treatable genetic neuropathy

Introduction

As opposed to CMT1, for which over 90% of cases have mutations in known genes, only 20–30% of CMT2/dHMN patients receive a genetic diagnosis. Since up to 70% of CMT2 and dHMN cases are sporadic, identifying candidate pathogenic genes from single cases remains challenging also for next-generation sequencing techniques.

Methods

We took advantage of the largest collection of over 1,100 CMT patients in whom WES and/or WGS has been performed in the GENESIS analysis platform. We specifically looked for genes for which significant DNA variants are present in multiple families as well as for individual alleles overrepresented in CMT cases.

Results

We identified 45 cases from 38 families across multiple ethnicities, carrying a particular nonsense mutation in SORD, c.753delG;p.Ala253GlnfsTer27, either in homozygous or compound heterozygous state with a second variant. With an allele frequency of 0.004 in healthy controls, the p.Ala253GlnfsTer27 variant represents one of the most common pathogenic alleles in humans. SORD is an enzyme that converts sorbitol into fructose, in the two-step polyol pathway that has been implicated in diabetic neuropathy. In patient-derived fibroblasts, we find a complete loss of SORD protein and increased intracellular sorbitol. Also, as a biomarker, serum fasting sorbitol level was over 100 times higher in patients compared to healthy individuals. In Drosophila, we show that loss of SORD orthologues causes synaptic degeneration and progressive motor impairment. Reducing the polyol influx by treatment with aldose reductase inhibi- tors normalized intracellular sorbitol levels in patient fibroblasts and in Drosophila, and also dramatically ameliorated motor and eye phenotypes.

Conclusions

We demonstrate biallelic mutations in sorbitol dehydrogenase (SORD) as the most frequent recessive form of hereditary neuropathies. These findings establish a potentially treatable cause in a sig- nificant fraction of patients with inherited neuropathies and may contribute to a better understanding of the pathophysiology of diabetic neuropathy.

andrea.cortese@ucl.ac.uk

1347. Comparison Between SARS-Cov-2, non-SARS-Cov-2 Coronavirus, Influenza and RSV Infections Among Solid Organ Transplant Recipients

Background

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has been raging since the end of 2019 and has shown worse outcomes in solid organ transplant recipients (SOTR). The clinical differences as well as outcomes between these respiratory viruses have not been well defined in SOTR.

Methods

This is a retrospective cohort study of adult SOTR with nasopharyngeal swab or bronchoalveolar lavage PCR positive for either SARS-CoV-2, non-SARS-CoV-2 coronavirus, influenza, or respiratory syncytial virus (RSV) from January 2017 to October 2020; both inpatient and outpatient. The follow up period was up to three months. Clinical characteristics and outcomes were evaluated. Development of lower respiratory tract infection (LRTI) was defined as new pulmonary infiltrates with or without symptoms. For statistical analysis, Fischer’s exact test and log rank test were performed.

Results

During study period, 157 SARS-CoV-2, 72 non-SARS-CoV-2 coronavirus, 100 influenza, 50 RSV infections were identified. Patient characteristics and outcomes are shown in tables 1 and 2, respectively. Secondary infections were not statistically significantly different between SARS-CoV-2 vs. non-SARS-CoV-2 coronavirus and influenza (p=0.25, 0.56) respectively, while it was statistically significant between SARS-CoV-2 and RSV (p=0.0009). Development of LRTI was higher in SARS-CoV-2 when compared to non-SARS-CoV-2 coronavirus (p=0.03), influenza (p=0.0001) and RSV (p=0.003). Admission to ICU was higher with SARS-CoV-2 compared to non-SARS-CoV-2 coronavirus (p=0.01), influenza (p=0.0001) and RSV (p=0.007). SARS-CoV-2 also had higher rates of mechanical ventilation when compared to non-SARS-CoV-2 coronavirus (p=0.01), influenza (p=0.01) and RSV (p=0.03). With time to event analysis, higher mortality with SARS-CoV-2 as compared to non-SARS-CoV-2 coronavirus, influenza, and RSV (p=0.01) was shown (Figure 1).

Conclusion

We found higher incidence of ICU admission, mechanical ventilation, and mortality among SARS-CoV-2 SOTR vs other respiratory viruses. To validate these results, multicenter study is warranted.

Disclosures

All Authors: No reported disclosures

A CADM3 variant causes Charcot-Marie-Tooth disease with marked upper limb involvement

The CADM family of proteins consists of four neuronal specific adhesion molecules (CADM1, CADM2, CADM3 and CADM4) that mediate the direct contact and interaction between axons and glia. In the peripheral nerve, axon-Schwann cell interaction is essential for the structural organization of myelinated fibres and is primarily mediated by the binding of CADM3, expressed in axons, to CADM4, expressed by myelinating Schwann cells. We have identified-by whole exome sequencing-three unrelated families, including one de novo patient, with axonal Charcot-Marie-Tooth disease (CMT2) sharing the same private variant in CADM3, Tyr172Cys. This variant is absent in 230 000 control chromosomes from gnomAD and predicted to be pathogenic. Most CADM3 patients share a similar phenotype consisting of autosomal dominant CMT2 with marked upper limb involvement. High resolution mass spectrometry analysis detected a newly created disulphide bond in the mutant CADM3 potentially modifying the native protein conformation. Our data support a retention of the mutant protein in the endoplasmic reticulum and reduced cell surface expression in vitro. Stochastic optical reconstruction microscopy imaging revealed decreased co-localization of the mutant with CADM4 at intercellular contact sites. Mice carrying the corresponding human mutation (Cadm3Y170C) showed reduced expression of the mutant protein in axons. Cadm3Y170C mice showed normal nerve conduction and myelin morphology, but exhibited abnormal axonal organization, including abnormal distribution of Kv1.2 channels and Caspr along myelinated axons. Our findings indicate the involvement of abnormal axon-glia interaction as a disease-causing mechanism in CMT patients with CADM3 mutations.

Assessing non-Mendelian inheritance in inherited axonopathies

PURPOSE

Inherited axonopathies (IA) are rare, clinically and genetically heterogeneous diseases that lead to length-dependent degeneration of the long axons in central (hereditary spastic paraplegia [HSP]) and peripheral (Charcot-Marie-Tooth type 2 [CMT2]) nervous systems. Mendelian high-penetrance alleles in over 100 different genes have been shown to cause IA; however, about 50% of IA cases do not receive a genetic diagnosis. A more comprehensive spectrum of causative genes and alleles is warranted, including causative and risk alleles, as well as oligogenic multilocus inheritance.

METHODS

Through international collaboration, IA exome studies are beginning to be sufficiently powered to perform a pilot rare variant burden analysis. After extensive quality control, our cohort contained 343 CMT cases, 515 HSP cases, and 935 non-neurological controls. We assessed the cumulative mutational burden across disease genes, explored the evidence for multilocus inheritance, and performed an exome-wide rare variant burden analysis.

RESULTS

We replicated the previously described mutational burden in a much larger cohort of CMT cases, and observed the same effect in HSP cases. We identified a preliminary risk allele for CMT in the EXOC4 gene (p value= 6.9 × 10-6, odds ratio [OR] = 2.1) and explored the possibility of multilocus inheritance in IA.

CONCLUSION

Our results support the continuing emergence of complex inheritance mechanisms in historically Mendelian disorders.

Author Correction: Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Biallelic mutations in SORD cause a common and potentially treatable hereditary neuropathy with implications for diabetes

Here we report biallelic mutations in the sorbitol dehydrogenase gene (SORD) as the most frequent recessive form of hereditary neuropathy. We identified 45 individuals from 38 families across multiple ancestries carrying the nonsense c.757delG (p.Ala253GlnfsTer27) variant in SORD, in either a homozygous or compound heterozygous state. SORD is an enzyme that converts sorbitol into fructose in the two-step polyol pathway previously implicated in diabetic neuropathy. In patient-derived fibroblasts, we found a complete loss of SORD protein and increased intracellular sorbitol. Furthermore, the serum fasting sorbitol levels in patients were dramatically increased. In Drosophila, loss of SORD orthologs caused synaptic degeneration and progressive motor impairment. Reducing the polyol influx by treatment with aldose reductase inhibitors normalized intracellular sorbitol levels in patient-derived fibroblasts and in Drosophila, and also dramatically ameliorated motor and eye phenotypes. Together, these findings establish a novel and potentially treatable cause of neuropathy and may contribute to a better understanding of the pathophysiology of diabetes.

POLG mutations presenting as Charcot-Marie-Tooth disease

We report on two patients, with different POLG mutations, in whom axonal neuropathy dominated the clinical picture. One patient presented with late onset sensory axonal neuropathy caused by a homozygous c.2243G>C (p.Trp748Ser) mutation that resulted from uniparental disomy of the long arm of chromosome 15. The other patient had a complex phenotype that included early onset axonal Charcot-Marie-Tooth disease (CMT) caused by compound heterozygous c.926G>A (p.Arg309His) and c.2209G>C (p.Gly737Arg) mutations.

Truncating Mutations in UBAP1 Cause Hereditary Spastic Paraplegia

The diagnostic gap for rare neurodegenerative diseases is still considerable, despite continuous advances in gene identification. Many novel Mendelian genes have only been identified in a few families worldwide. Here we report the identification of an autosomal-dominant gene for hereditary spastic paraplegia (HSP) in 10 families that are of diverse geographic origin and whose affected members all carry unique truncating changes in a circumscript region of UBAP1 (ubiquitin-associated protein 1). HSP is a neurodegenerative disease characterized by progressive lower-limb spasticity and weakness, as well as frequent bladder dysfunction. At least 40% of affected persons are currently undiagnosed after exome sequencing. We identified pathological truncating variants in UBAP1 in affected persons from Iran, USA, Germany, Canada, Spain, and Bulgarian Roma. The genetic support ranges from linkage in the largest family (LOD = 8.3) to three confirmed de novo mutations. We show that mRNA in the fibroblasts of affected individuals escapes nonsense-mediated decay and thus leads to the expression of truncated proteins; in addition, concentrations of the full-length protein are reduced in comparison to those in controls. This suggests either a dominant-negative effect or haploinsufficiency. UBAP1 links endosomal trafficking to the ubiquitination machinery pathways that have been previously implicated in HSPs, and UBAP1 provides a bridge toward a more unified pathophysiology.

A novel MFN2 mutation causes variable clinical severity in a multi-generational CMT2 family

Dominant mutations in MFN2 cause a range of phenotypes, including severe, early-onset axonal neuropathy, "classical CMT2", and late-onset axonal neuropathy. We found a novel MFN2 mutation - c.283A>G (p.Arg95Gly) - that results in an axonal neuropathy with variable clinical severity in a multigenerational family. In affected family members, electromyography showed moderate to severe, chronic denervation in distal muscles. Such variable clinical severity highlights the need to do careful assessments of at risk individuals when assessing MFN2 variants.

Identification of a new SYT2 variant validates an unusual distal motor neuropathy phenotype

Objective

To report a new SYT2 missense mutation causing distal hereditary motor neuropathy and presynaptic neuromuscular junction (NMJ) transmission dysfunction.

Methods

We report a multigenerational family with a new missense mutation, c. 1112T>A (p. Ile371Lys), in the C2B domain of SYT2, describe the clinical and electrophysiologic phenotype associated with this variant, and validate its pathogenicity in a Drosophila model.

Results

Both proband and her mother present a similar clinical phenotype characterized by a slowly progressive, predominantly motor neuropathy and clear evidence of presynaptic NMJ dysfunction on nerve conduction studies. Validation of this new variant was accomplished by characterization of the mutation homologous to the human c. 1112T>A variant in Drosophila, confirming its dominant-negative effect on neurotransmitter release.

Conclusions

This report provides further confirmation of the role of SYT2 in human disease and corroborates the resultant unique clinical phenotype consistent with heriditary distal motor neuropathy. SYT2-related motor neuropathy is a rare disease but should be suspected in patients presenting with a combination of presynaptic NMJ dysfunction (resembling Lambert-Eaton myasthenic syndrome) and a predominantly motor neuropathy, especially in the context of a positive family history.

Mutations in ATP1A1 Cause Dominant Charcot-Marie-Tooth Type 2

Although mutations in more than 90 genes are known to cause CMT, the underlying genetic cause of CMT remains unknown in more than 50% of affected individuals. The discovery of additional genes that harbor CMT2-causing mutations increasingly depends on sharing sequence data on a global level. In this way-by combining data from seven countries on four continents-we were able to define mutations in ATP1A1, which encodes the alpha1 subunit of the Na⁺,K⁺-ATPase, as a cause of autosomal-dominant CMT2. Seven missense changes were identified that segregated within individual pedigrees: c.143T>G (p.Leu48Arg), c.1775T>C (p.Ile592Thr), c.1789G>A (p.Ala597Thr), c.1801_1802delinsTT (p.Asp601Phe), c.1798C>G (p.Pro600Ala), c.1798C>A (p.Pro600Thr), and c.2432A>C (p.Asp811Ala). Immunostaining peripheral nerve axons localized ATP1A1 to the axolemma of myelinated sensory and motor axons and to Schmidt-Lanterman incisures of myelin sheaths. Two-electrode voltage clamp measurements on Xenopus oocytes demonstrated significant reduction in Na⁺ current activity in some, but not all, ouabain-insensitive ATP1A1 mutants, suggesting a loss-of-function defect of the Na⁺,K⁺ pump. Five mutants fall into a remarkably narrow motif within the helical linker region that couples the nucleotide-binding and phosphorylation domains. These findings identify a CMT pathway and a potential target for therapy development in degenerative diseases of peripheral nerve axons.