Electrocardiographic findings in children with spinal muscular atrophy

AAV9-mediated SMN gene therapy rescues cardiac desmin but not lamin A/C and elastin dysregulation in Smn2B/- spinal muscular atrophy mice

Structural, functional and molecular cardiac defects have been reported in spinal muscular atrophy (SMA) patients and mouse models. Previous quantitative proteomics analyses demonstrated widespread molecular defects in the severe Taiwanese SMA mouse model. Whether such changes are conserved across different mouse models, including less severe forms of the disease, has yet to be established. Here, using the same high-resolution proteomics approach in the less-severe Smn2B/- SMA mouse model, 277 proteins were found to be differentially abundant at a symptomatic timepoint (post-natal day (P) 18), 50 of which were similarly dysregulated in severe Taiwanese SMA mice. Bioinformatics analysis linked many of the differentially abundant proteins to cardiovascular development and function, with intermediate filaments highlighted as an enriched cellular compartment in both datasets. Lamin A/C was increased in the cardiac tissue, whereas another intermediate filament protein, desmin, was reduced. The extracellular matrix (ECM) protein, elastin, was also robustly decreased in the heart of Smn2B/- mice. AAV9-SMN1-mediated gene therapy rectified low levels of survival motor neuron protein and restored desmin levels in heart tissues of Smn2B/- mice. In contrast, AAV9-SMN1 therapy failed to correct lamin A/C or elastin levels. Intermediate filament proteins and the ECM have key roles in cardiac function and their dysregulation may explain cardiac impairment in SMA, especially since mutations in genes encoding these proteins cause other diseases with cardiac aberration. Cardiac pathology may need to be considered in the long-term care of SMA patients, as it is unclear whether currently available treatments can fully rescue peripheral pathology in SMA.

Review of cardiac safety in onasemnogene abeparvovec gene replacement therapy: translation from preclinical to clinical findings

Human gene replacement therapies such as onasemnogene abeparvovec (OA) use recombinant adeno-associated virus (rAAV) vectors to treat monogenic disorders. The heart and liver are known target organs of toxicity in animals; with cardiac and hepatic monitoring recommended in humans after OA dosing. This manuscript provides a comprehensive description of cardiac data from preclinical studies and clinical sources including clinical trials, managed access programs and the post-marketing setting following intravenous OA administration through 23 May 2022. Single dose mouse GLP-Toxicology studies revealed dose-dependent cardiac findings including thrombi, myocardial inflammation and degeneration/regeneration, which were associated with early mortality (4-7 weeks) in the high dose groups. No such findings were documented in non-human primates (NHP) after 6 weeks or 6 months post-dose. No electrocardiogram or echocardiogram abnormalities were noted in NHP or humans. After OA dosing, some patients developed isolated elevations in troponin without associated signs/symptoms; the reported cardiac adverse events in patients were considered of secondary etiology (e.g. respiratory dysfunction or sepsis leading to cardiac events). Clinical data indicate cardiac toxicity observed in mice does not translate to humans. Cardiac abnormalities have been associated with SMA. Healthcare professionals should use medical judgment when evaluating the etiology and assessment of cardiac events post OA dosing so as to consider all possibilities and manage the patient accordingly.

Cardiac pathology in spinal muscular atrophy: a systematic review

Background

Hereditary proximal spinal muscular atrophy (SMA) is a severe neuromuscular disease of childhood caused by homozygous loss of function of the survival motor neuron (SMN) 1 gene. The presence of a second, nearly identical SMN gene (SMN2) in the human genome ensures production of residual levels of the ubiquitously expressed SMN protein. Alpha-motor neurons in the ventral horns of the spinal cord are most vulnerable to reduced SMN concentrations but the development or function of other tissues may also be affected, and cardiovascular abnormalities have frequently been reported both in patients and SMA mouse models.

Methods

We systematically reviewed reported cardiac pathology in relation to SMN deficiency. To investigate the relevance of the possible association in more detail, we used clinical classification systems to characterize structural cardiac defects and arrhythmias.

Conclusions

Seventy-two studies with a total of 264 SMA patients with reported cardiac pathology were identified, along with 14 publications on SMA mouse models with abnormalities of the heart. Structural cardiac pathology, mainly septal defects and abnormalities of the cardiac outflow tract, was reported predominantly in the most severely affected patients (i.e. SMA type 1). Cardiac rhythm disorders were most frequently reported in patients with milder SMA types (e.g. SMA type 3). All included studies lacked control groups and a standardized approach for cardiac evaluation.

The convergence to specific abnormalities of cardiac structure and function may indicate vulnerability of specific cell types or developmental processes relevant for cardiogenesis. Future studies would benefit from a controlled and standardized approach for cardiac evaluation in patients with SMA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-017-0613-5) contains supplementary material, which is available to authorized users.

Spinal muscular atrophy: a motor neuron disorder or a multi-organ disease?

Spinal muscular atrophy (SMA) is an autosomal recessive disorder that is the leading genetic cause of infantile death. SMA is characterized by loss of motor neurons in the ventral horn of the spinal cord, leading to weakness and muscle atrophy. SMA occurs as a result of homozygous deletion or mutations in Survival Motor Neuron-1 (SMN1). Loss of SMN1 leads to a dramatic reduction in SMN protein, which is essential for motor neuron survival. SMA disease severity ranges from extremely severe to a relatively mild adult onset form of proximal muscle atrophy. Severe SMA patients typically die mostly within months or a few years as a consequence of respiratory insufficiency and bulbar paralysis. SMA is widely known as a motor neuron disease; however, there are numerous clinical reports indicating the involvement of additional peripheral organs contributing to the complete picture of the disease in severe cases. In this review, we have compiled clinical and experimental reports that demonstrate the association between the loss of SMN and peripheral organ deficiency and malfunction. Whether defective peripheral organs are a consequence of neuronal damage/muscle atrophy or a direct result of SMN loss will be discussed.

Type III spinal muscular atrophy mimicking muscular dystrophies

Types III and IV spinal muscular atrophy represent a diagnostic challenge due to the great variability in their presentation. We report a series of eight patients with type III spinal muscular atrophy who were followed for a long time for possible muscular dystrophy or myopathy, confirming its clinical heterogeneity and propensity to delayed diagnosis. Clinical examination revealed heterogeneous findings, where the diagnosis of type III spinal muscular atrophy was not immediately apparent in many patients as their clinical and laboratory abnormalities were consistent with muscular dystrophy or myopathy. The presence of dystrophic features such as hypertrophy of the calves, weakness of the limb girdle, high serum creatine kinase levels, and myopathic histopathology should not divert attention from the possibility of spinal muscular atrophy. It is strongly recommended to give variable presentations enough thought and to consider the autosomal recessive type III spinal muscular atrophy in the diagnostic evaluation.

Medical considerations of long-term survival of Werdnig-Hoffmann disease

OBJECTIVES

To report intercurrent nonrespiratory complications of unprecedented survival for Werdnig-Hoffman disease (spinal muscular atrophy type 1 [SMA 1]).

DESIGN

A retrospective chart review and caregiver questionnaire for 103 consecutively referred SMA 1 patients for whom death was prevented during infancy.

RESULTS

Overall, 15 of 63 (23.8%) respondents had severe, symptomatic bradycardias. Thirteen of 25 males had bilateral cryptorchidism, and two were unilateral. Ten of 42 (24%) respondents had recurrent oral candidiasis, and eight (19.0%) had recurrent nonoral candidiasis. All patients had hip dislocation/subluxation. They had collapsing spines and scoliosis by 1 yr of age. Ninety-six had indwelling gastrostomy/nasogastric tubes before 24 mos of age. Twenty-six underwent fundoplication to decrease reflux. Fifty-seven were on modified elemental diets with reported benefits. About one half had early pubarche. Three patients had episodes of acute pancreatitis. One untreated patient died of candidal endocarditis at 4 mos of age, and a second child had mitral valve candidiasis on autopsy.

CONCLUSION

Prolonged survival of SMA 1 results in a high incidence of concomitant medical conditions that need to be addressed.