Motor function performance in individuals with RYR1-related myopathies

Long-term Natural History of Pediatric Dominant and Recessive RYR1-Related Myopathy

BACKGROUND AND OBJECTIVES

RYR1-related myopathies are the most common congenital myopathies, but long-term natural history data are still scarce. We aim to describe the natural history of dominant and recessive RYR1-related myopathies.

METHODS

A cross-sectional and longitudinal retrospective data analysis of pediatric cases with RYR1-related myopathies seen between 1992-2019 in 2 large UK centers. Patients were identified, and data were collected from individual medical records.

RESULTS

Sixty-nine patients were included in the study, 63 in both cross-sectional and longitudinal studies and 6 in the cross-sectional analysis only. Onset ranged from birth to 7 years. Twenty-nine patients had an autosomal dominant RYR1-related myopathy, 31 recessive, 6 de novo dominant, and 3 uncertain inheritance. Median age at the first and last appointment was 4.0 and 10.8 years, respectively. Fifteen% of patients older than 2 years never walked (5 recessive, 4 de novo dominant, and 1 dominant patient) and 7% lost ambulation during follow-up. Scoliosis and spinal rigidity were present in 30% and 17% of patients, respectively. Respiratory involvement was observed in 22% of patients, and 12% needed ventilatory support from a median age of 7 years. Feeding difficulties were present in 30% of patients, and 57% of those needed gastrostomy or tube feeding. There were no anesthetic-induced malignant hyperthermia episodes reported in this cohort. We observed a higher prevalence of prenatal/neonatal features in recessive patients, in particular hypotonia and respiratory difficulties. Clinical presentation, respiratory outcomes, and feeding outcomes were consistently more severe at presentation and in the recessive group. Conversely, longitudinal analysis suggested a less progressive course for motor and respiratory function in recessive patients. Annual change in forced vital capacity was -0.2%/year in recessive vs -1.4%/year in dominant patients.

DISCUSSION

This clinical study provides long-term data on disease progression in RYR1-related myopathies that may inform management and provide essential milestones for future therapeutic interventions.

Ryanodine Receptor 1-Related Myopathies: Quantification of Intramuscular Fatty Infiltration from T1-Weighted MRI

Background:

Ryanodine receptor 1-related myopathy (RYR1-RM) can present with a selective pattern and gradient of intramuscular fatty infiltration (IMFI) on magnetic resonance imaging (MRI).

Objective:

To demonstrate an automated protocol for quantification of IMFI in the lower extremity muscles of individuals with RYR1-RM using T1-weighted MRI and to examine the relationships of IMFI with motor function and clinical severity.

Methods:

Axial images of the lower extremity muscles were acquired by T1-weighted fast spin-echo and short tau inversion recovery (STIR) sequences. A modified ImageJ-based program was used for quantification. IMFI data was analyzed by mode of inheritance, motor function, and clinical severity.

Results:

Upper and lower leg IMFI from 36 genetically confirmed and ambulatory RYR1-RM affected individuals (26 dominant and 10 recessive) were analyzed using Grey-scale quantification. There was no statistically significant difference in IMFI between dominant and recessive cases in upper or lower legs. IMFI in both upper and lower legs was inversely correlated with participant performance on the motor function measure (MFM-32) total score (upper leg: p < 0.001; lower leg: p = 0.003) and the six-minute walk test (6MWT) distance (upper leg: p < 0.001; lower leg: p = 0.010). There was no significant difference in mean IMFI between participants with mild versus severe clinical phenotypes (p = 0.257).

Conclusion:

A modified ImageJ-based algorithm was able to select and quantify fatty infiltration in a cohort of heterogeneously affected individuals with RYR1-RM. IMFI was not predictive of mode of inheritance but showed strong correlation with motor function and capacity tests including MFM-32 and 6MWT, respectively.

Progression or Not - A Small Natural History Study of Genetical Confirmed Congenital Myopathies

BACKGROUND

Clinical characteristics of patients with congenital myopathies (CM) are well known but there is a lack of knowledge about the natural history and course of disease of the different genetic subtypes. In 2010 we assessed the national cohort of Danish patients with CM to decide genetic diagnosing and describe genotype- phenotype relationships.AIM of this follow-up study was to evaluate the course of disease since the initial study and to evaluate the applicability of standard assessment methods to reflect change over time and patients own opinion on the course of disease.

METHODS

All available genetically diagnosed patients studied by us in 2010 (n = 41) were invited to the follow-up study; assessment of motor function (MFM-32), muscle strength (MRC %)and respiratory function (FVC %) and prime assessor were the same as in the initial study. Patients were asked whether the course of disease had progresses, was stable or had improved.

RESULTS

23 patients (15-61 y) accepted the invitation. Mean follow-up time was 7.7 years. Loss of muscle strength was more prominent in patients with mutations in DNM2, RYR1 and TPM2/3 genes and deterioration in FVC % was more evident in patients carrying NEB and ACTA1 gene mutations. MFM-sum score was less sensitive to change compared to MRC-sum score. In general, agreement between the patient's own opinion of the course of disease and results of assessments was good.

CONCLUSION

The number of patients in the study is too small to be conclusive, but the results indicate that CM can be stable or slowly progressive depending on the genetic subtype.

Is Exercise-Induced Fatigue a Problem in Children with Duchenne Muscular Dystrophy?

OBJECTIVE

Duchenne muscular dystrophy (DMD) is a devastating X-linked muscular disorder. The number of studies investigating new therapeutic approaches is substantially increasing. This study aims to investigate the impact and diagnostic value of exercise-induced fatigue in DMD, which has been proposed as a suitable outcome parameter in other conditions like spinal muscular atrophy.

PATIENTS AND METHODS

A cohort of 55 DMD patients (49 of them treated with steroids and 9 with ataluren) underwent a total of 241 6MWT (mean 4.4 tests/patient) which were retrospectively analyzed. Exercise-induced fatigue was assessed by the ratio between the distance achieved in the sixth minute and the distance in the second minute of the 6MWT. In previous studies a quotient above 1 was defined as a sign of fatigue.

RESULTS

The average fatigue quotient in the whole cohort of patients was 1.0. In a further analysis no impact of age, steroid therapy, ataluren therapy, overall disability, and distance in the 6-minute walk test (6MWT) on fatigue in DMD patients could be shown.

CONCLUSION

Our data show that fatigue does not play a relevant role in DMD. Analysis of fatigue is not a useful outcome parameter in DMD studies. For this reason we suggest the 2MWT, which is better accepted by the patients, as an alternative to the commonly 6MWT.