Spinal muscular atrophy within Amish and Mennonite populations: Ancestral haplotypes and natural history

The influence of genotype on the natural history of types 1 - 3 spinal muscular atrophy

The severity of spinal muscular atrophy (SMA) is inversely correlated with the number of survival of motor neuron 2 (SMN2) copies an individual has. This observational, retrospective analysis of natural history data included untreated individuals with a genetic diagnosis of types 1-3 SMA and stratified disease-related characteristics by SMN2 copy number. The outcomes investigated were time to: death, permanent ventilation, respiratory support, feeding support, scoliosis surgery, and achievement and loss of motor milestones. Of 134 individuals; 33 had two SMN2 copies and 101 had 3 or more copies. Survival was linked to increasing SMN2 copy number: mean age at death for individuals with two SMN2 copies was 8 months (standard deviation [SD]: 4 months) and 10 years (SD: 5 months) for individuals with three copies, and no deaths were reported in individuals with ≥4 SMN2 copies. Increasing SMN2 copy number was linked to a longer time to permanent ventilation, respiratory support, feeding support, and scoliosis, as well as loss of motor milestones. SMA disease-related endpoints showed distinct patterns between groups with differing SMN2 copy numbers. Prediction and assessment of disease progression may be stratified by SMN2 copy number, which will be important for evaluating the impact of treatment.

Development and assessment of educational materials for spinal muscular atrophy carrier screening in the Plain community

Spinal muscular atrophy (SMA) has been reported in both Amish and Mennonite (Plain) communities, and a higher incidence has been observed in certain Mennonite communities compared to the general population. There are several therapies for SMA, but all are most effective in pre-symptomatic newborns. To identify couples from the Wisconsin Plain community who are most likely to have a child with SMA, carrier screening is offered via mailed kits with at-home specimen collection. Our survey data about Plain families' perspectives on genetic testing suggest educational materials are needed for individuals providing informed consent with at-home specimen collection. We therefore developed a Plain population-specific educational trifold brochure about SMA carrier screening by incorporating existing medical education strategies and feedback from Plain community members and their health care providers. Along with the brochure, surveys were included in the kits to assess baseline knowledge about SMA carrier screening ("pre-education") as well as improvement in knowledge after reviewing the brochure and cultural appropriateness of the brochure ("post-education"). Fifty-five testing kits were distributed, and 26 survey pairs (pre- and post-education) were returned and analyzed (response rate 47%). Respondents had high baseline knowledge with an average of 5 of 7 questions (71%) answered correctly on the pre-education survey. Knowledge improved after reviewing the brochure as the average score increased to 6.5 of 7 questions (93%) answered correctly. Questions about risks of having an affected child after positive or negative carrier screening showed the most improvement from the pre-education to post-education surveys. Most respondents indicated the brochure was helpful, was easy to understand, and contained the right amount of information. Overall, incorporating elements of existing medical education strategies with feedback from the target population and stakeholders about appropriate language seems to be an effective method for creating beneficial, culturally responsive educational materials for the Plain population.

The impact of three SMN2 gene copies on clinical characteristics and effect of disease-modifying treatment in patients with spinal muscular atrophy: a systematic literature review

Objective

To review the clinical characteristics and effect of treatment in patients with spinal muscular atrophy (SMA) and three copies of the SMN2 gene.

Methods

We conducted a literature search in October 2022 to identify English-language clinical research on SMA that included SMN2 copy number according to PRISMA guidelines.

Results

Our search identified 44 studies examining the impact of three SMN2 copies on clinical characteristics (21 on phenotype, 13 on natural history, and 15 on functional status and other signs/symptoms). In children with type I SMA or presymptomatic infants with an SMN1 deletion, three SMN2 copies was associated with later symptom onset, slower decline in motor function and longer survival compared with two SMN2 copies. In patients with SMA type II or III, three SMN2 copies is associated with earlier symptom onset, loss of ambulation, and ventilator dependence compared with four SMN2 copies. Eleven studies examined treatment effects with nusinersen (nine studies), onasemnogene abeparvovec (one study), and a range of treatments (one study) in patients with three SMN2 copies. In presymptomatic infants, early treatment delayed the onset of symptoms and maintained motor function in those with three SMN2 copies. The impact of copy number on treatment response in symptomatic patients is still unclear.

Conclusion

SMN2 copy number is strongly correlated with SMA phenotype in patients with SMN1 deletion, while no correlation was found in patients with an SMN1 mutation. Patients with three SMN2 copies show a highly variable clinical phenotype. Early initiation of treatment is highly effective in presymptomatic patients with three SMN2 copies.

Motor and neurocognitive profiles of children with symptomatic spinal muscular atrophy type 1 with two copies of SMN2 before and after treatment: a longitudinal observational study

Introduction

Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by mutations in the survival motor neuron 1 (SMN1) gene. In clinical studies, gene replacement therapy with onasemnogene abeparvovec (formerly AVXS-101, Zolgensma®, Novartis) was efficacious in improving motor functioning in children with SMA. However, its effects on cognitive and language skills are largely unknown.

Methods

This longitudinal observational study evaluated changes in motor and neurocognitive functioning over a 1-year period after administration of onasemnogene abeparvovec in 12 symptomatic SMA type 1 patients with two copies of SMN2 aged 1.7-52.6 months at administration. Motor functioning was measured using the Children's Hospital of Philadelphia Infant Test for Neuromuscular Disorders (CHOP-INTEND) while neurocognitive assessment was measured using Griffiths III. Motor milestones and language ability were also assessed at each timepoint.

Results and discussion

Statistically significant increases in median CHOP-INTEND scores from baseline were observed at 1, 3, 6, and 12 months after onasemnogene abeparvovec administration (all p ≤ 0.005). Most (91.7%) patients were able to roll over or sit independently for >1 min at 12 months. Significant increases in the Griffiths III Foundations of Learning, Language and Communication, Eye and Hand Coordination, and Personal-Social-Emotional subscale scores were observed at 12-months, but not in the Gross Motor subscale. Speech and language abilities progressed in most patients. Overall, most patients showed some improvement in cognitive and communication performance after treatment with onasemnogene abeparvovec in addition to significant improvement in motor functioning and motor milestones. Evaluation of neurocognitive function should be considered when assessing the global functioning of patients with SMA.

A Systematic Literature Review of the Natural History of Respiratory, Swallowing, Feeding, and Speech Functions in Spinal Muscular Atrophy (SMA)

Background

Respiratory and bulbar dysfunctions (including swallowing, feeding, and speech functions) are key symptoms of spinal muscular atrophy (SMA), especially in its most severe forms. Demonstrating the long-term efficacy of disease-modifying therapies (DMTs) necessitates an understanding of SMA natural history.

Objective

This study summarizes published natural history data on respiratory, swallowing, feeding, and speech functions in patients with SMA not receiving DMTs.

Methods

Electronic databases (Embase, MEDLINE, and Evidence-Based Medicine Reviews) were searched from database inception to June 27, 2022, for studies reporting data on respiratory and/or bulbar function outcomes in Types 1-3 SMA. Data were extracted into a predefined template and a descriptive summary of these data was provided.

Results

Ninety-one publications were included: 43 reported data on respiratory, swallowing, feeding, and/or speech function outcomes. Data highlighted early loss of respiratory function for patients with Type 1 SMA, with ventilatory support typically required by 12 months of age. Patients with Type 2 or 3 SMA were at risk of losing respiratory function over time, with ventilatory support initiated between the first and fifth decades of life. Swallowing and feeding difficulties, including choking, chewing problems, and aspiration, were reported in patients across the SMA spectrum. Swallowing and feeding difficulties, and a need for non-oral nutritional support, were reported before 1 year of age in Type 1 SMA, and before 10 years of age in Type 2 SMA. Limited data relating to other bulbar functions were collated.

Conclusions

Natural history data demonstrate that untreated patients with SMA experience respiratory and bulbar function deterioration, with a more rapid decline associated with greater disease severity. This study provides a comprehensive repository of natural history data on bulbar function in SMA, and it highlights that consistent assessment of outcomes in this area is necessary to benefit understanding and approval of new treatments.

Systematic Literature Review of the Natural History of Spinal Muscular Atrophy: Motor Function, Scoliosis, and Contractures

BACKGROUND AND OBJECTIVES

Spinal muscular atrophy (SMA) is a progressive neuromuscular disorder associated with continuous motor function loss and complications, such as scoliosis and contractures. Understanding the natural history of SMA is key to demonstrating the long-term outcomes of SMA treatments. This study reviews the natural history of motor function, scoliosis, and contractures in patients with SMA.

METHODS

Electronic databases were searched from inception to June 27, 2022 (Embase, MEDLINE, and Evidence-Based Medicine Reviews). Observational studies, case-control studies, cross-sectional studies, and case series reporting on motor function (i.e., sitting, standing, and walking ability), scoliosis, and contracture outcomes in patients with types 1-3 SMA were included. Data on study design, baseline characteristics, and treatment outcomes were extracted. Data sets were generated from studies that reported Kaplan-Meier (KM) curves and pooled to generate overall KM curves.

RESULTS

Ninety-three publications were included, of which 68 reported on motor function. Of these, 10 reported KM curves (3 on the probability of sitting in patients with types 2 and 3 SMA and 8 on the probability of walking/ambulation in patients with type 3 SMA). The median time to loss of sitting (95% CI) was 14.5 years (14.1-31.5) for the type 2 SMA sitter population (their maximum ability was independent sitting). The median time to loss of ambulation (95% CI) was 13.4 years (12.5-14.5) for type 3a SMA (disease onset at age younger than 3 years) and 44.2 years (43.0-49.4) for type 3b SMA (disease onset at age 3 years or older). Studies including scoliosis and contracture outcomes mostly reported non-time-to-event data.

DISCUSSION

The results demonstrate that a high degree of motor function loss is inevitable, affecting patients of all ages. In addition, data suggest that untreated patients with types 2 and 3 SMA remain at risk of losing motor milestones during late adulthood, and patients with types 3a and 3b SMA are at risk of loss of ambulation over time. These findings support the importance of stabilization of motor function development even at older ages. Natural history data are key for the evaluation of SMA treatments as they contextualize the assessment of long-term outcomes.

Exploratory evaluation of an eye-tracking system in patients with advanced spinal muscular atrophy type I receiving nusinersen

Objective

This study evaluated the feasibility of a matching-pair test using eye-tracking technology to assess nusinersen effectiveness in patients with advanced spinal muscular atrophy (SMA) type I.

Methods

This prospective, observational study enrolled patients with 5q-SMA type I who had lost gross motor function. Three different levels of matching-pair tests were conducted using the eye-gaze system (My Tobii; TobiiDynavox Inc.) at baseline, and after 9 and 24 weeks of nusinersen treatment. The primary endpoint was the change from baseline in matching-pair test scores and response times (i.e., the time to answer matching-pair test) at 24 weeks from baseline. Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND), Pediatric Quality of Life inventory for patients with Neuromuscular Disease (PedsQL-NM) and Numerical Rating Scale (NRS) scores were also assessed as secondary endpoints. Analysis of ocular fixation was performed as an additional analysis. This study was registered at https://www.umin.ac.jp/ctr/ (UMIN000033935).

Results

Seven patients (one male, six female) aged 5–21 years (median 11 years) were enrolled; all patients were bedridden and six patients were ventilated. All seven patients were able to conduct level 1 matching-pair tests at each assessment; five patients were also able to conduct levels 2 and 3. Two patients (those with the highest CHOP-INTEND scores) were able to complete all tests correctly within 60 s. There was a non-significant trend toward improvement in CHOP-INTEND, PedsQL-NM, and NRS scores over the 6-month period. There were no significant differences in the number of actions, errors, correct answers, or response times between baseline and Week 9 or 24 at any level. However, the result of an additional analysis suggests that detection of eye movement would be useful to evaluate for advanced SMA.

Conclusions

Eye-tracking systems are possibly feasible for the assessment of treatment efficacy in patients with advanced SMA type I.

Mendelian disease research in the Plain populations of Lancaster County, Pennsylvania

Founder populations have long contributed to our knowledge of rare disease genes and phenotypes. From the pioneering work of Dr. Victor McKusick to today, research in these groups has shed light on rare recessive phenotypes, expanded the clinical spectrum of disease, and facilitated disease gene identification. Current clinical and research studies in these special groups augment the wealth of knowledge already gained, provide new insights into emerging problems such as variant interpretation and reduced penetrance, and contribute to the development of novel therapies for rare genetic diseases. Clinical developments over the past 30 years have altered the fundamental relationship with the Lancaster Plain communities: research has become more collaborative, and the knowledge imparted by these studies is now being harnessed to provide cutting-edge translational medicine to the very community of vulnerable individuals who need it most.