Limb-girdle myopathy and mild intellectual disability: The expanding spectrum of TANGO2-related disease.

TANGO2-related disease is an autosomal recessive multisystem disease associated with developmental delay and infancy-onset recurrent metabolic crises with early mortality. Several studies have reported dysfunction in endoplasmic reticulum-to-Golgi traffic and mitochondrial homoeostasis as the underlying pathophysiology. We report a 40-year-old woman affected by limb-girdle weakness and mild intellectual disability caused by the recurrent deletion of exons 3-9 in homozygosity in the TANGO2 gene. Physical examination revealed hyperlordosis, waddling gait, calf pseudohypertrophy, and Aquilian tendon retractions. Laboratory investigations revealed elevation of serum biomarkers suggestive of mitochondrial dysfunction together with hypothyroidism. At the age of 24, the patient suffered a metabolic crisis with severe rhabdomyolysis and malignant cardiac arrhythmia. After recovery, no metabolic or arrhythmic crisis has recurred. Muscle histology two years later revealed increased endomysial fibrosis and other myopathic changes. Our findings illustrate the mildest end of the phenotypic spectrum of TANGO2-related disease and reveal further aspects related to chronic muscle damage in this disorder.

Identification of two novel RRM2B variants associated with autosomal recessive progressive external ophthalmoplegia in a family with pseudodominant inheritance pattern.

RRM2B encodes the p53-inducible small subunit (p53R2) of ribonucleotide reductase, a key protein for mitochondrial DNA (mtDNA) synthesis. Pathogenic variants in this gene result in familial mitochondrial disease in adults and children, secondary to a maintenance disorder of mtDNA. This study describes two patients, mother and son, with early-onset chronic progressive external ophthalmoplegia (PEO). Skeletal muscle biopsy from the latter was examined: cytochrome c oxidase (COX)-negative fibres were shown, and molecular studies revealed multiple mtDNA deletions. A next-generation sequencing gene panel for nuclear-encoded mitochondrial maintenance genes identified two unreported heterozygous missense variants (c.514 G > A and c.682 G > A) in the clinically affected son. The clinically affected mother harboured the first variant in homozygous state, and the clinically unaffected father harboured the remaining variant in heterozygous state. In silico analyses predicted both variants as deleterious. Cell culture studies revealed that patients' skin fibroblasts, but not fibroblasts from healthy controls, responded to nucleoside supplementation with enhanced mtDNA repopulation, thus suggesting an in vitro functional difference in patients' cells. Our results support the pathogenicity of two novel RRM2B variants found in two patients with autosomal recessive PEO with multiple mtDNA deletions inherited with a pseudodominant pattern.

Chronic progressive external ophthalmoplegia plus syndrome due to homozygous missense variant in TOP3A gene.

Chronic progressive external ophthalmoplegia (CPEO) plus syndrome due to pathogenic biallelic variants in TOP3A gene has been described in only one single patient. We report two adult siblings with c.614A>G (p.Asp205Gly) homozygous missense variant in the TOP3A gene who had CPEO plus syndrome.

An Atypical Presentation of Upper Motor Neuron Predominant Juvenile Amyotrophic Lateral Sclerosis Associated with TARDBP Gene: A Case Report and Review of the Literature.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that can rarely affect young individuals. Juvenile ALS (JALS) is defined for individuals with an onset of the disease before the age of 25. The contribution of genetics to ALS pathology is a field of growing interest. One of the differences between adult-onset ALS and JALS is their genetic background, with a higher contribution of genetic causes in JALS. We report a patient with JALS and a pathogenic variant in the TARDBP gene (c.1035C > G; p.Asn345Lys), previously reported only in adult-onset ALS, and with an atypical phenotype of marked upper motor neuron predominance. In addition, the proband presented an additional variant in the NEK1 gene, c.2961C > G (p.Phe987Leu), which is classified as a variant of unknown significance. Segregation studies showed a paternal origin of the TARDBP variant, while the variant in NEK1 was inherited from the mother. We hypothesize that the NEK1 variant acts as a disease modifier and suggests the possibility of a functional interaction between both genes in our case. This hypothesis could explain the peculiarities of the phenotype, penetrance, and the age of onset. This report highlights the heterogeneity of the phenotypic presentation of ALS associated with diverse pathogenic genetic variants.

COVID-19 in multiple sclerosis patients: susceptibility, severity risk factors and serological response.

BACKGROUND AND PURPOSE: Information regarding multiple sclerosis (MS) patients with the 2019 novel coronavirus disease (COVID-19) is scarce. The study objective was to describe the incidence and characteristics of MS patients with COVID-19, to identify susceptibility and severity risk factors and to assess the proportion of positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serologies according to disease-modifying treatments. METHODS: This was a retrospective study of an MS cohort analysing data collected between February and May 2020. Cases were identified through an email survey and clinical visits. The relationship of demographic and MS characteristics with COVID-19 and of the disease-modifying treatments with SARS-CoV-2 serostatus were examined. RESULTS: Data from 48 suspected cases out of 758 valid respondents and from 45 COVID-19 cases identified through clinical visits were collected. Incidence was 6.3%. Nineteen (20.3%) patients were hospitalized and two (2.2%) died. Multivariable models determined that age (odds ratio [OR] per 10 years 0.53, 95% confidence interval [CI] 0.34-0.85), contact with a confirmed case (OR 197.02, 95% CI 56.36-688.79), residence in Barcelona (OR 2.23, 95% CI 1.03-4.80), MS duration (OR per 5 years 1.41, 95% CI 1.09-1.83) and time on anti-CD20 treatment (OR per 2 years 3.48, 95% CI 1.44-8.45) were independent factors for presenting COVID-19 and age (OR per 10 years 2.71, 95% CI 1.13-6.53) for a severe COVID-19. Out of the 79 (84.9%) with serological test, 45.6% generated antibodies, but only 17.6% of those on anti-CD20 therapies. Lymphopaenia or immunoglobulin levels did not relate to COVID-19. CONCLUSIONS: Multiple sclerosis patients present similar incidence, risk factors and outcomes for COVID-19 as the general population. Patients treated with an anti-CD20 therapy for a longer period of time might be at a higher risk of COVID-19 and less than 20% generate an antibody response. Only age was related to severity.