The expanding clinical and genetic spectrum of DYNC1H1-related disorders.

Intracellular trafficking involves an intricate machinery of motor complexes including the dynein complex to shuttle cargo for autophagolysosomal degradation. Deficiency in dynein axonemal chains as well as cytoplasmic light and intermediate chains have been linked with ciliary dyskinesia and skeletal dysplasia. The cytoplasmic dynein 1 heavy chain protein (DYNC1H1) serves as a core complex for retrograde trafficking in neuronal axons. Dominant pathogenic variants in DYNC1H1 have been previously implicated in peripheral neuromuscular disorders (NMD) and neurodevelopmental disorders (NDD). As heavy-chain dynein is ubiquitously expressed, the apparent selectivity of heavy-chain dyneinopathy for motor neuronal phenotypes remains currently unaccounted for. Here, we aimed to evaluate the full DYNC1H1-related clinical, molecular and imaging spectrum, including multisystem features and novel phenotypes presenting throughout life. We identified 47 cases from 43 families with pathogenic heterozygous variants in DYNC1H1 (aged 0-59 years) and collected phenotypic data via a comprehensive standardized survey and clinical follow-up appointments. Most patients presented with divergent and previously unrecognized neurological and multisystem features, leading to significant delays in genetic testing and establishing the correct diagnosis. Neurological phenotypes include novel autonomic features, previously rarely described behavioral disorders, movement disorders, and periventricular lesions. Sensory neuropathy was identified in nine patients (median age of onset 10.6 years), of which five were only diagnosed after the second decade of life, and three had a progressive age-dependent sensory neuropathy. Novel multisystem features included primary immunodeficiency, bilateral sensorineural hearing loss, organ anomalies, and skeletal manifestations, resembling the phenotypic spectrum of other dyneinopathies. We also identified an age-dependent biphasic disease course with developmental regression in the first decade and, following a period of stability, neurodegenerative progression after the second decade of life. Of note, we observed several cases in whom neurodegeneration appeared to be prompted by intercurrent systemic infections with double-stranded DNA viruses (Herpesviridae) or single-stranded RNA viruses (Ross-River fever, SARS-CoV-2). Moreover, the disease course appeared to be exacerbated by viral infections regardless of age and/or severity of NDD manifestations, indicating a role of dynein in anti-viral immunity and neuronal health. In summary, our findings expand the clinical, imaging, and molecular spectrum of pathogenic DYNC1H1 variants beyond motor neuropathy disorders and suggest a life-long continuum and age-related progression due to deficient intracellular trafficking. This study will facilitate early diagnosis and improve counselling and health surveillance of affected patients.

Hip Displacement in Spinal Muscular Atrophy: The Influences of Genetic Severity, Functional Level, and Disease-modifying Treatments.

PURPOSE: Hip displacement (HD) is common in spinal muscular atrophy (SMA), but neither genetic severity nor gross motor function level have been investigated as risk factors. Although disease-modifying agents (DMA) have improved function and overall health, their effects on the prevention of HD are unknown. The purpose of this study was to determine risk factors for HD development in SMA. METHODS: Retrospective cohort. Children with SMA presenting between January 2005 and August 2021, at least 1 hip radiograph, and a minimum 2-year follow-up were included. The primary outcome measure was the prevalence of HD (migration percentage ≥40%). Secondary outcomes included SMA type (I/II/III), survival motor neuron 2 copy number, Hammersmith Functional Motor Scale (HFMS, out of 66), ambulatory status (Functional Mobility Scale at 50 m), clinically relevant scoliosis (>40 degrees and/or surgery), and DMA treatment (>1-year duration, nusinersen/risdiplam/onasemnogene abeparvovec) as risk factors. Univariate and multivariate logistic regression analyses were performed. RESULTS: Eighty-two patients (52% female) with SMA type I (n=32, 39%), II (n=36, 44%), and III (n=14, 17%) met the inclusion criteria, with a final follow-up of 4.5 (SD: 2.7) years. Age at first hip radiograph was 3.4 (SD: 2.9) years. The prevalence of HD was 75.6%, with a mean age of onset of 4.6 (SD: 2.7) years. When stratified by SMA type, the prevalence/age of onset (mean, years) was 84%/3.1 (SD: 1.7), 80%/5.8 (SD: 2.3), and 36%/9.0 (SD: 4.3), respectively. HFMS score >23 was protective against HD by receiver operating characteristic analysis ( P =0.008). Significant risk factors by univariate analysis were SMA type I ( P =0.002) and II ( P =0.002), HFMS ≤23 ( P =0.01), nonambulatory status (Functional Mobility Scale at 50 m = 1, P =0.001), clinically relevant scoliosis ( P =0.01), and DMA treatment ( P =0.01). By multivariate analysis, only SMA type II ( P =0.04) and scoliosis ( P =0.04) were independent risk factors. CONCLUSIONS: The prevalence of HD in SMA is highly linked to disease severity. Identified risk factors can be used in the development of surveillance programs for early detection of HD in SMA, allowing for timely management. LEVEL OF EVIDENCE: Level III.

No difference in postoperative complication rates or cardiopulmonary function for early versus late scoliosis correction in Duchenne muscular dystrophy.

BACKGROUND: Given reduced rates of both pulmonary function decline and scoliosis progression with steroid treatment in Duchenne muscular dystrophy (DMD), the role of early scoliosis surgery has been questioned. The purpose of this study was to compare the postoperative complication rates of early versus late scoliosis correction in DMD. METHODS: This study was a retrospective cohort, conducted at an academic tertiary level children's hospital. Patients with DMD who underwent posterior scoliosis correction, with preoperative pulmonary function testing [forced vital capacity (FVC)] were included and divided into two groups by preoperative curve angles: ≤ 45° and > 45°. The primary outcome variable was postoperative complications by Clavien-Dindo classification grading. Secondary outcome variables included postoperative complications occurring after the first 90 days, age at surgery, duration of wheelchair dependency preoperatively, pulmonary function, steroid utilization, shortening fraction by echocardiogram, surgery duration, intensive care unit/hospital length of stay, days intubated, infection, and percent curve correction. Two-tailed t-test and Chi-square testing were used for analysis of patient factors and Clavien-Dindo complication grade, respectively. RESULTS: Thirty-one patients were included with a total follow-up of 8.3 ± 3.2 years, 4.8 ± 2.2 years post-spinal fusion. Steroid treatment (prednisone, deflazacort) was utilized for 21 (67.7%) patients. Primary curve correction was not different between groups (65.0% vs 71.4% [p = 0.37]). There were no significant differences in Clavien-Dindo classification grades between groups (p > 0.05). For the entire cohort, the overall complication rate was higher for patients with steroid treatment (61.9% vs 10.0% [p = 0.008]). Neither forced vital capacity nor fractional shortening on echocardiogram was different between groups at final follow-up (p = 0.6 and p = 0.4, respectively). CONCLUSION: The comparable risk of perioperative complications for early and late scoliosis correction supports a "watchful waiting" approach, whereby curves less than 45° can be carefully followed while cardiopulmonary function is maintained. Patients undergoing steroid treatment should be counseled regarding the higher risk of postoperative blood transfusion and deep wound infection. LEVEL OF EVIDENCE: III Retrospective cohort.

Critical Airway Stenosis in an Adolescent Male With Pompe Disease and Thoracic Lordosis: A Case Report.

An adolescent male with late-onset Pompe disease (glycogen storage disease type II) presented with a history of restrictive airway disease and a near-cardiorespiratory arrest during anesthesia for a liver biopsy initially thought to be due to bronchospasm. During a subsequent posterior spinal fusion procedure, he suffered cardiorespiratory arrest resulting in the procedure being aborted. Bronchoscopy performed shortly after resuscitation revealed an undiagnosed narrowing of the distal trachea and bronchi. This is the first description of a patient with late-onset Pompe disease with undiagnosed critical tracheal stenosis due to the progression of thoracic lordosis, which was ultimately relieved by posterior spinal fusion.

Nephroblastomatosis or Wilms tumor in a fourth patient with a somatic PIK3CA mutation.

Wilms tumor and nephroblastomatosis are associated with syndromic conditions including hemihyperplasia. Hemihyperplasia is genetically heterogeneous and may be the result of genomic abnormalities seen in Beckwith-Wiedemann syndrome, mosaic chromosome or genomic abnormalities, or somatic point mutations. Somatic missense mutations affecting the PI3K-AKT-MTOR pathway result in segmental overgrowth and are present in numerous benign and malignant tumors. Here, we report a fourth patient with asymmetric overgrowth due to a somatic PIK3CA mutation who had nephroblastomatosis or Wilms tumor. Similar to two of three reported patients with a somatic PIK3CA mutation and renal tumors, he shared a PIK3CA mutation affecting codon 1047, presented at birth with asymmetric overgrowth, and had fibroadipose overgrowth. Codon 1047 is most commonly affected by somatic mutations in PIK3CA-related overgrowth spectrum (PROS). While the fibroadipose overgrowth phenotype appears to be common in individuals with PIK3CA mutations at codon 1047, individuals with a clinical diagnosis of Klippel-Trenaunay syndrome or isolated lymphatic malformation also had mutations affecting this amino acid. Screening for Wilms tumor in individuals with PROS-related hemihyperplasia may be considered and, until the natural history is fully elucidated in larger cohort studies, may follow guidelines for Beckwith-Wiedemann syndrome, or isolated hemihyperplasia. It is not known if the specific PIK3CA mutation, the mosaic distribution, or the clinical presentation affect the Wilms tumor or nephroblastomatosis risk in individuals with PROS. © 2016 Wiley Periodicals, Inc.

GMPPB-Associated Dystroglycanopathy: Emerging Common Variants with Phenotype Correlation.

Mutations in GDP-mannose pyrophosphorylase B (GMPPB), a catalyst for the formation of the sugar donor GDP-mannose, were recently identified as a cause of muscular dystrophy resulting from abnormal glycosylation of α-dystroglycan. In this series, we report nine unrelated individuals with GMPPB-associated dystroglycanopathy. The most mildly affected subject has normal strength at 25 years, whereas three severely affected children presented in infancy with intellectual disability and epilepsy. Muscle biopsies of all subjects are dystrophic with abnormal immunostaining for glycosylated α-dystroglycan. This cohort, together with previously published cases, allows preliminary genotype-phenotype correlations to be made for the emerging GMPPB common variants c.79G>C (p.D27H) and c.860G>A (p.R287Q). We observe that c.79G>C (p.D27H) is associated with a mild limb-girdle muscular dystrophy phenotype, whereas c.860G>A (p.R287Q) is associated with a relatively severe congenital muscular dystrophy typically involving brain development. Sixty-six percent of GMPPB families to date have one of these common variants.

Increased susceptibility of spinal muscular atrophy fibroblasts to camptothecin is p53-independent.

BACKGROUND: Deletion or mutation(s) of the survival motor neuron 1 (SMN1) gene causes spinal muscular atrophy (SMA). The SMN protein is known to play a role in RNA metabolism, neurite outgrowth, and cell survival. Yet, it remains unclear how SMN deficiency causes selective motor neuron death and muscle atrophy seen in SMA. Previously, we have shown that skin fibroblasts from SMA patients are more sensitive to the DNA topoisomerase I inhibitor camptothecin, supporting a role for SMN in cell survival. Here, we examine the potential mechanism of camptothecin sensitivity in SMA fibroblasts. RESULTS: Camptothecin treatment reduced the DNA relaxation activity of DNA topoisomerase I in human fibroblasts. In contrast, kinase activity of DNA topoisomerase I was not affected by camptothecin, because levels of phosphorylated SR proteins were not decreased. Upon camptothecin treatment, levels of p53 were markedly increased. To determine if p53 plays a role in the increased sensitivity of SMA fibroblasts to camptothecin, we analyzed the sensitivity of SMA fibroblasts to another DNA topoisomerase I inhibitor, beta-lapachone. This compound is known to induce death via a p53-independent pathway in several cancer cell lines. We found that beta-lapachone did not induce p53 activation in human fibroblasts. In addition, SMA and control fibroblasts showed essentially identical sensitivity to this compound. By immunofluorescence staining, SMN and p53 co-localized in gems within the nucleus, and this co-localization was overall reduced in SMA fibroblasts. However, depletion of p53 by siRNA did not lessen the camptothecin sensitivity in SMA fibroblasts. CONCLUSION: Even though p53 and SMN are associated, the increased sensitivity of SMA fibroblasts to camptothecin does not occur through a p53-dependent mechanism.

Clinical, histological and genetic characterization of reducing body myopathy caused by mutations in FHL1.

We recently identified the X-chromosomal four and a half LIM domain gene FHL1 as the causative gene for reducing body myopathy, a disorder characterized by progressive weakness and intracytoplasmic aggregates in muscle that exert reducing activity on menadione nitro-blue-tetrazolium (NBT). The mutations detected in FHL1 affected highly conserved zinc coordinating residues within the second LIM domain and lead to the formation of aggregates when transfected into cells. Our aim was to define the clinical and morphological phenotype of this myopathy and to assess the mutational spectrum of FHL1 mutations in reducing body myopathy in a larger cohort of patients. Patients were ascertained via the detection of reducing bodies in muscle biopsy sections stained with menadione-NBT followed by clinical, histological, ultrastructural and molecular genetic analysis. A total of 11 patients from nine families were included in this study, including seven sporadic patients with early childhood onset disease and four familial cases with later onset. Weakness in all patients was progressive, sometimes rapidly so. Respiratory failure was common and scoliosis and spinal rigidity were significant in some of the patients. Analysis of muscle biopsies confirmed the presence of aggregates of FHL1 positive material in all biopsies. In two patients in whom sequential biopsies were available the aggregate load in muscle sections appeared to increase over time. Ultrastructural analysis revealed that cytoplasmic bodies were regularly seen in conjunction with the reducing bodies. The mutations detected were exclusive to the second LIM domain of FHL1 and were found in both sporadic as well as familial cases of reducing body myopathy. Six of the nine mutations affected the crucial zinc coordinating residue histidine 123. All mutations in this residue were de novo and were associated with a severe clinical course, in particular in one male patient (H123Q). Mutations in the zinc coordinating residue cysteine 153 were associated with a milder phenotype and were seen in the familial cases in which the boys were still more severely affected compared to their mothers. We expect the mild end of the spectrum to significantly expand in the future. On the severe end of the spectrum we define reducing body myopathy as a progressive disease with early, but not necessarily congenital onset, distinguishing this condition from the classic essentially non-progressive congenital myopathies.

Increased susceptibility of spinal muscular atrophy fibroblasts to camptothecin-induced cell death.

Spinal muscular atrophy (SMA) is a neuromuscular disease caused by deletions or mutations in the telomeric copy of the survival motor neuron (SMN1) gene. Although the SMN protein has been implicated in the biogenesis of ribonucleoprotein complexes and RNA processing, it is not clear how these functions contribute to the pathogenesis of SMA. To gain a further understanding of SMN function, we have investigated its role in cell survival in skin fibroblasts derived from SMA patients and age-matched controls. SMA fibroblasts exposed to camptothecin, a specific inhibitor of DNA topoisomerase I, consistently showed cell death at a lower concentration than normal controls. Treatment with other cell death-inducing agents did not cause differences in survival of SMA fibroblasts as compared with control fibroblasts. Camptothecin treatment resulted in activation of caspase-3 with generation of the caspase-3 cleavage product, poly ADP-ribose polymerase (PARP). Depletion of SMN protein by RNA interference in control fibroblasts increased caspase-3 activity, whereas transfection of SMA fibroblasts with wild-type SMN decreased caspase-3 activity. Our data demonstrate that SMA fibroblasts are more prone to some, but not all, death-stimuli. Vulnerability to death-stimuli is associated with decreased levels of SMN protein and is mediated by activation of caspase-3.