A previously unreported NARS1 variant causes dominant distal hereditary motor neuropathy in a French family.

BACKGROUND AND AIMS: Pathogenic variants in the NARS1 gene, which encodes for the asparaginyl-tRNA synthetase1 (NARS1) enzyme, were associated with complex central and peripheral nervous system phenotypes. Recently, Charcot-Marie-Tooth (CMT) disease has been linked to heterozygous pathogenic variants in NARS1 in nine patients. Here, we report two brothers and their mother from a French family with distal hereditary motor neuropathy (dHMN) carrying a previously unreported NARS1 variant. METHODS: The NARS1 variant (c.1555G>C; p.(Gly519Arg)) was identified through whole-genome sequencing (WGS) performed on the family members. Clinical findings, nerve conduction studies (NCS), needle electromyography (EMG), and functional assays in yeast complementation assays are reported here. RESULTS: The family members showed symptoms of dHMN, including distal weakness and osteoarticular deformities. They also exhibited brisk reflexes suggestive of upper motor neuron involvement. All patients were able to walk independently at the last follow-up. NCS and EMG confirmed pure motor neuropathy. Functional assays in yeast confirmed a loss-of-function effect of the variant on NARS1 activity. INTERPRETATION: Our findings expand the clinical spectrum of NARS1-associated neuropathies, highlighting the association of NARS1 mutations with dHMN. The benign disease course observed in our patients suggests a slowly progressive phenotype. Further reports could contribute to a more comprehensive understanding of the spectrum of NARS1-associated neuropathies.

The significance of multidisciplinary team meetings in diagnosing and managing childhood interstitial lung disease within the RespiRare network.

INTRODUCTION: Childhood Interstitial Lung Disease (chILD) represents a rare and severe group of diseases for which the etiologic workup, classification, and management remain a challenge for most pediatric pulmonologists. In France in 2018, the RespiRare network established the first multidisciplinary team meetings (MDTm) dedicated to chILD. This study aims to investigate the impact of MDTm in chILD diagnosis and management as well as user satisfaction. METHODS: The MDTm took place on a monthly basis through video conferences. The participants consisted of a quorum and included pediatric pulmonologists, radiologists, geneticists, and pulmonologists, with an average of 10.5 participants per meeting. Patients provided consent to participate in MDTm and for data collection. Data were retrospectively extracted from MDTm reports. To evaluate the usefulness of the MDTm and the satisfaction of the participants, a survey was sent by email at least 3 months after the MDTm to the participants. RESULTS: A total of 216 chILD cases were discussed during 56 MDTm sessions. The median age of onset was 0.5 years (interquartile range 0-7). The MDTm sessions resulted in the correction of chILD etiology in 25% of cases (neuroendocrine cell hyperplasia of infancy 17%, surfactant metabolism disorder 8%, pulmonary alveolar proteinosis 4%, hemosiderosis 3%, sarcoidosis 3%, and others 34%), and chILD was ruled out in 7% of cases. A change in therapy was proposed for 46% of cases. User satisfaction was significant, particularly regarding their confidence in managing these rare diseases. DISCUSSION AND CONCLUSION: Dedicated MDTm sessions offer a unique opportunity to enhance chILD etiologic diagnosis and management, leading to increased physician knowledge and confidence in managing these patients.

Idiopathic pulmonary fibrosis with benign SFTPC variant and pathogenic MARS1 mutations: can't see the forest for the trees!

Even in the absence of liver disease, MARS1 screening should be considered in severe lung fibrosis of young individuals. Interpretation of the genetic variants can evolve with improvement of knowledge (databases, bioinformatic tools) over time. https://bit.ly/45OxF5E.

Congenital surfactant protein B (SP-B) deficiency: a case report.

The incapacity to synthesize certain components of pulmonary surfactant causes a heterogeneous group of rare respiratory diseases called genetic disorders of surfactant dysfunction. We report a female full-term infant with neonatal respiratory distress of early onset due to inherited SP-B deficiency. The infant failed oxygen weaning at multiple trials. Chest computed tomography was performed on the 29th day of life revealing ground-glass opacities, regular interlobular septal thickening and fine interlobular reticulations. Analysis of genomic DNA showed homozygosity for an extremely rare SFTPB gene variant (c.620A>G, p.Tyr207Cys). Both parents were heterozygotes for the mutation. The diagnosis of congenital SP-B deficiency should be suspected whenever an early and acute respiratory failure in a term or near-term infant does not resolve after five days of age: diagnostic confirmation can be easily and rapidly obtained with the analysis of genomic DNA.

Inherited pulmonary surfactant metabolism disorders in Argentina: Differences between patients with SFTPC and ABCA3 variants.

BACKGROUND: Patients with inherited pulmonary surfactant metabolism disorders have a wide range of clinical outcomes and imaging findings. Response to current anti-inflammatory therapies has been variable and efficacy is unclear. OBJECTIVE: To describe and compare genetic, clinical, histological, and computed tomography (CT) outcomes in a cohort of patients with variants in the genes encoding surfactant protein C (SP-C) or adenosine triphosphate-binding cassette transporter A3 (ABCA3) in Argentina. METHODS: Observational cohort retrospective study. Patients carrying variants in genes encoding SP-C and ABCA3 proteins were included. RESULTS: Fourteen patients met the inclusion criteria: SFTPC n = 6, ABCA3 n = 8 (seven were heterozygous and one compound heterozygous). Neonatal respiratory distress was more frequent and severe in neonates with variants in the ABCA3 gene. The onset of the disease occurred in infancy before the age of 20 months in all cases. Patients with ABCA3 pathogenic variants had a severe clinical course, while long-term outcomes were more favorable in individuals with SFTPC variants. Initial CT findings were ground glass opacities and intraparenchymal cysts in both groups. Over time, signs of lung fibrosis were present in 57% of patients with ABCA3 variants and in 33% of the SFTPC group. The efficacy of anti-inflammatory interventions appears to be poor, especially for patients with ABCA3 pathogenic variants. CONCLUSIONS: Clinical, histological, and radiological features are similar in patients with SFTPC and ABCA3 variants; however, the latter have more severe clinical course. Current anti-inflammatory regimens do not appear to stop the progression of the disease.

Variable Expression of Lung Disease Due to a Novel Homozygous ABCA3 Variant.

Background: Mutations in the ATP-binding cassette transporter A3 (ABCA3) gene are one of the most common surfactant disorders leading to interstitial lung diseases (ILD). The clinical spectrum and severity of lung disease caused by ABCA3 deficiency due to missense variants is variable. Case Presentations: A novel ABCA3 c.3135G>C (p.Gln1045His) mutation was identified at the homozygous state in 3 subjects from 2 unrelated families: one 19-month-old boy with severe ILD and his homozygous pauci-symptomatic mother, and one 10-year-old girl with moderate late-onset ILD. Corticosteroid pulses associated with hydroxychloroquine were beneficial for both children. Conclusion: We illustrate here the huge intra- and interfamilial phenotypic variability associated with the same homozygous missense ABCA3 mutation, and the benefit of identifying the disease for treatment, follow-up, and appropriate genetic counseling.

Difficulties in the treatment of an infant survivor with inherited surfactant protein-B deficiency in Tunisia.

A female-term neonate showed a severe respiratory distress syndrome (RDS) at hour 3 of life requiring her transfer to intensive care. She was intubated and started on assist-control mechanical ventilation associated with inhaled nitric oxide then high-frequency oscillation ventilation at day 12. Chest X-ray was gradually deteriorating. Chest computed tomography (CT) scan revealed diffuse interstitial lung disease. Flexible bronchoscopy excluded pulmonary alveolar proteinosis. The genetics study confirmed surfactant protein-B (SP-B) deficiency caused by the novel homozygous c.770T>C, p.Leu257Pro mutation in the SFTPB gene (NM_000542.5). Methylprednisolone pulse therapy was administered from day 20. As the infant worsened, azithromycin, sildenafil, and inhaled steroids were added at the age of 6 months and azathioprine at the age of 10 months. At the age of 12 months, chest CT showed diffuse "crazy-paving." The infant died of respiratory failure at the age of 13 months. Unexplained neonatal RDS should raise the suspicion of SP-B disease. This novel mutation could be part of the mutations allowing partial SP-B production result in prolonged survival. Lung transplant in infants, unavailable in numerous countries, remains the unique way to reverse the fatal outcome.

Deciphering an isolated lung phenotype of NKX2-1 frameshift pathogenic variant.

Background: to perform a functional analysis of a new NK2 homeobox 1 (NKX2-1) variant (c.85_86del denominated NKX2-1DEL) identified in a family presenting with isolated respiratory disease, in comparison to another frameshift variant (c.254dup denominated NKX2-1DUP) identified in a subject with classical brain-lung-thyroid syndrome. Methods: pathogenic variants were introduced into the pcDNA3-1(+)-wt-TTF1 plasmid. The proteins obtained were analyzed by western blot assay. Subcellular localization was assessed by confocal microscopy in A549 and Nthy cells. Transactivation of SFTPA, SFTPB, SFTPC, and ABCA3 promoters was assessed in A549 cells. Thyroglobulin promoter activity was measured with the paired box gene 8 (PAX8) cofactor in Nthy cells. Results: The two sequence variants were predicted to produce aberrant proteins identical from the 86th amino acid, with deletion of their functional homeodomain, including the nuclear localization signal. However, 3D conformation prediction of the conformation prediction of the mutant protein assumed the presence of a nuclear localization signal, a bipartite sequence, confirmed by confocal microscopy showing both mutant proteins localized in the nucleus and cytoplasm. Transcriptional activity with SFTPA, SFTPB, SFTPC, ABCA3 and thyroglobulin promoters was significantly decreased with both variants. However, with NKX2-1DEL, thyroglobulin transcriptional activity was maintained with the addition of PAX8. Conclusion: These results provide novel insights into understanding the molecular mechanism of phenotypes associated with NKX2-1 pathogenic variants.

Structure-Based Understanding of ABCA3 Variants.

ABCA3 is a crucial protein of pulmonary surfactant biosynthesis, associated with recessive pulmonary disorders such as neonatal respiratory distress and interstitial lung disease. Mutations are mostly private, and accurate interpretation of variants is mandatory for genetic counseling and patient care. We used 3D structure information to complete the set of available bioinformatics tools dedicated to medical decision. Using the experimental structure of human ABCA4, we modeled at atomic resolution the human ABCA3 3D structure including transmembrane domains (TMDs), nucleotide-binding domains (NBDs), and regulatory domains (RDs) in an ATP-bound conformation. We focused and mapped known pathogenic missense variants on this model. We pinpointed amino-acids within the NBDs, the RDs and within the interfaces between the NBDs and TMDs intracellular helices (IHs), which are predicted to play key roles in the structure and/or the function of the ABCA3 transporter. This theoretical study also highlighted the possible impact of ABCA3 variants in the cytosolic part of the protein, such as the well-known p.Glu292Val and p.Arg288Lys variants.

Prenatal Ultrasound Suspicion of Cystic Fibrosis in a Multiethnic Population: Is Extensive CFTR Genotyping Needed?

In families without a Cystic Fibrosis (CF) history, fetal ultrasound bowel abnormalities can unexpectedly reveal the disease. Isolated or in association, the signs can be fetal bowel hyperechogenicity, intestinal loop dilatation and non-visualization of fetal gallbladder. In these cases, search for CF transmembrane conductance regulator (CFTR) gene mutations is part of the recommended diagnostic practices, with a search for frequent mutations according to ethnicity, and, in case of the triad of signs, with an exhaustive study of the gene. However, the molecular diagnosis remains a challenge in populations without well-known frequent pathogenic variants. We present a multiethnic cohort of 108 pregnancies with fetal bowel abnormalities in which the parents benefited from an exhaustive study of the CFTR gene. We describe the new homozygous p.Cys1410* mutation in a fetus of African origin. We did not observe the most frequent p.Phe508del mutation in our cohort but evidenced variants undetected by our frequent mutations kit. Thanks to the progress of sequencing techniques and despite the difficulties of interpretation occasionally encountered, we discuss the need to carry out a comprehensive CFTR study in all patients in case of fetal bowel abnormalities.

Clinical and Molecular Spectrum Associated with COL6A3 c.7447A>G p.(Lys2483Glu) Variant: Elucidating its Role in Collagen VI-related Myopathies.

BACKGROUND: Dominant and recessive autosomal pathogenic variants in the three major genes (COL6A1-A2-A3) encoding the extracellular matrix protein collagen VI underlie a group of myopathies ranging from early-onset severe conditions (Ullrich congenital muscular dystrophy) to milder forms maintaining independent ambulation (Bethlem myopathy). Diagnosis is based on the combination of clinical presentation, muscle MRI, muscle biopsy, analysis of collagen VI secretion, and COL6A1-A2-A3 genetic analysis, the interpretation of which can be challenging. OBJECTIVE: To refine the phenotypical spectrum associated with the frequent COL6A3 missense variant c.7447A>G (p.Lys2483Glu). METHODS: We report the clinical and molecular findings in 16 patients: 12 patients carrying this variant in compound heterozygosity with another COL6A3 variant, and four homozygous patients. RESULTS: Patients carrying this variant in compound heterozygosity with a truncating COL6A3 variant exhibit a phenotype consistent with COL6-related myopathies (COL6-RM), with joint contractures, proximal weakness and skin abnormalities. All remain ambulant in adulthood and only three have mild respiratory involvement. Most show typical muscle MRI findings. In five patients, reduced collagen VI secretion was observed in skin fibroblasts cultures. All tested parents were unaffected heterozygous carriers. Conversely, two out of four homozygous patients did not present with the classical COL6-RM clinical and imaging findings. Collagen VI immunolabelling on cultured fibroblasts revealed rather normal secretion in one and reduced secretion in another. Muscle biopsy from one homozygous patient showed myofibrillar disorganization and rimmed vacuoles. CONCLUSIONS: In light of our results, we postulate that the COL6A3 variant c.7447A>G may act as a modulator of the clinical phenotype. Thus, in patients with a typical COL6-RM phenotype, a second variant must be thoroughly searched for, while for patients with atypical phenotypes further investigations should be conducted to exclude alternative causes. This works expands the clinical and molecular spectrum of COLVI-related myopathies.

Hereditary sensory autonomic neuropathy type II: Report of two novel mutations in the FAM134B gene.

Hereditary sensory autonomic neuropathy (HSAN) type II is a rare, autosomal recessive, and early onset sensory neuropathy, characterized by severe and progressive sensation impairment, leading to ulcero-mutilating complications. FAM134B gene, also known as RETREG1 gene, mutations have been reported to be associated to HSAN-IIB. We report four patients from two unrelated families who developed during childhood a sensory axonal neuropathy with variable severity and pronounced nociception impairment. Complications such as recurrent ulcerations, osteomyelitis, and osteonecrosis leading to distal amputation were noticed. Dysautonomia was mild or even absent in our group of patients. Additionally, either clinical or neurophysiological motor impairment was not uncommon. Presence of upper motor neuron signs was also a distinctive feature in two related patients. After extensive workup, two novel homozygous mutations in the FAM134B gene were identified. This report expands the clinical and genetic spectrum of HSAN type II and emphasizes the phenotype variability even within the same family.

The most frequent ABCA3 nonsense mutation -p.Tyr1515* (Y1515X) causing lethal neonatal respiratory failure in a term neonate.

Defects in the surfactant biosynthesis are associated with respiratory distress syndrome, commonly occurring in premature infants due to lung immaturity. However, interstitial lung diseases have also been observed in full-term infants with mutations in the SFTPC, SFTPB, NKX2-1, or ABCA3 genes, involved in the surfactant metabolism. Herein, we report a newborn baby with neonatal respiratory distress and diffuse lung disease caused by ABCA3 mutation. The baby died at 5 weeks of age after developing pulmonary hypertension. Genomic DNA was analyzed for four genes involved in surfactant metabolism out of which the c. 4545C>G (p.Tyr1515*) homozygous mutation in exon 29 of ABCA3 was identified which is one of the most frequent mutation causing lethal neonatal respiratory failure in a term neonate. This case study emphasizes the importance of raising awareness about this diagnosis in the clinical settings for fruitful outcomes in health-care delivery.

Heterogeneity of lung disease associated with NK2 homeobox 1 mutations.

We retrospectively studied the clinical presentation, treatment modalities and outcome in 16 patients with heterozygous NKX2-1 mutation associated with chronic lung disease. Twelve different NKX2-1 mutations, including 4 novel mutations, were identified in the 16 patients. Nine patients presented with brain-lung-thyroid syndrome, 3 had neurological and lung symptoms and 4 had only pulmonary symptoms. Ten patients had neonatal respiratory distress, and 6 of them developed infiltrative lung disease (ILD). The other patients were diagnosed with ILD in childhood (n = 3) or in adulthood (n = 3). The median age at diagnosis was 36 months (IQ 3.5-95). Patient testing included HRCT (n = 13), BALF analysis (n = 6), lung biopsies (n = 3) and lung function tests (n = 6). Six patients required supplemental oxygen support with a median duration of 18 months (IQ 2.5-29). All symptomatic ILD patients (n = 12) benefited from a treatment consisting of steroids, azithromycin (n = 9), and/or hydroxychloroquine (n = 4). The median follow-up was 36 months (IQ 24-71.5). One patient died of respiratory failure at 18 months and another is waiting for lung transplantation. In summary, the initial diagnosis was based on clinical presentation and radiological features, but the presentation was heterogeneous. Definitive diagnosis required genetic analysis, which should be performed, even in absence of neurological or thyroid symptoms.

Correlation between PABPN1 genotype and disease severity in oculopharyngeal muscular dystrophy.

OBJECTIVE: Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant adult-onset disease characterized by progressive ptosis, dysphagia, and proximal limb weakness. The genetic cause is an expanded (GCN)n mutation in the PABPN1 gene encoding for the polyadenylate-binding protein nuclear 1. We hypothesized a potential correlation between the size of the (GCN)n expansion and the severity of the phenotype. To do this, we characterized the distribution of the genotypes as well as their correlation with age at diagnosis and phenotypical features in a large cohort of heterozygous and homozygous patients with OPMD in France with a confirmed molecular diagnosis of PABPN1. METHODS: We explored 354 unrelated index cases recruited between 1999 and 2014 in several neuromuscular centers in France. RESULTS: This cohort allowed us to characterize the frequency of mutated alleles in the French population and to demonstrate a statistical correlation between the size of the expansion and the mean age at diagnosis. We also confirmed that homozygous patients present with a more severe disease. CONCLUSIONS: It has been difficult to establish phenotype-genotype correlations because of the rare nature of this disease. Our work demonstrates that patients with OPMD with longer PABPN1 expansion are on average diagnosed at an earlier age than patients with a shorter expansion, confirming that polyalanine expansion size plays a role in OPMD, with an effect on disease severity and progression.