Results from a 3-year Non-interventional, Observational Disease Monitoring Program in Adults with GNE Myopathy

Pharmacokinetics and clinical efficacy of 6'-sialyllactose in patients with GNE myopathy: Randomized pilot trial

GNE myopathy, caused by biallelic mutations in the GNE gene, is characterized by initial ankle dorsiflexor weakness and rimmed vacuoles in the muscle histopathology, resulting in reduced sialic acid production. Sialyllactose is a source of sialic acid. We performed a pilot clinical trial to analyze the pharmacokinetic properties of 6'-sialyllactose (6SL) and evaluated the safety, and efficacy of oral 6SL in patients with GNE myopathy. Ten participants were in the pharmacokinetic study, and 20 in the subsequent clinical trial. For the pharmacokinetic study, participants were administered either 3 g (low-dose) or 6 g (high-dose) of 6SL in a single dose. Plasma concentrations of 6SL, sialic acid, and sialic acid levels on the surface of red blood cells were periodically assessed in blood samples. Patients were randomly allocated to test (low- and high-dose groups) or placebo groups for the trial. Motor function, ambulation, plasma 6SL and sialic acid concentrations, GNE myopathy-functional activity scale scores, and MRI findings were assessed. 6SL was well tolerated, except for self-limited gastrointestinal discomfort. Free sialic acid in both low- and high-dose groups significantly increased at 6 and 12 weeks, but not in the placebo group. In the high-dose group, proximal limb powers improved with daily 6SL. Considering the fat fraction on muscle MRI, results in the high-dose group were superior to those in the low-dose group. 6SL may be a good candidate for GNE myopathy therapeutics as it induces an increase or reduces the decrease in limb muscle power, attenuates muscle degeneration, and improves the biochemical properties of sialic acid.

Efficacy confirmation study of aceneuramic acid administration for GNE myopathy in Japan

BACKGROUND

A rare muscle disease, GNE myopathy is caused by mutations in the GNE gene involved in sialic acid biosynthesis. Our recent phase II/III study has indicated that oral administration of aceneuramic acid to patients slows disease progression.

METHODS

We conducted a phase III, randomized, placebo-controlled, double-blind, parallel-group, multicenter study. Participants were assigned to receive an extended-release formulation of aceneuramic acid (SA-ER) or placebo. Changes in muscle strength and function over 48 weeks were compared between treatment groups using change in the upper extremity composite (UEC) score from baseline to Week 48 as the primary endpoint and the investigator-assessed efficacy rate as the key secondary endpoint. For safety, adverse events, vital signs, body weight, electrocardiogram, and clinical laboratory results were monitored.

RESULTS

A total of 14 patients were enrolled and given SA-ER (n = 10) or placebo (n = 4) tablets orally. Decrease in least square mean (LSM) change in UEC score at Week 48 with SA-ER (- 0.115 kg) was numerically smaller as compared with placebo (- 2.625 kg), with LSM difference (95% confidence interval) of 2.510 (- 1.720 to 6.740) kg. In addition, efficacy was higher with SA-ER as compared with placebo. No clinically significant adverse events or other safety concerns were observed.

CONCLUSIONS

The present study reproducibly showed a trend towards slowing of loss of muscle strength and function with orally administered SA-ER, indicating supplementation with sialic acid might be a promising replacement therapy for GNE myopathy.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov (NCT04671472).

Phase II/III Study of Aceneuramic Acid Administration for GNE Myopathy in Japan

BACKGROUND

GNE myopathy is an ultra-rare muscle disease characterized by a reduction in the synthesis of sialic acid derived from pathogenic variants in the GNE gene. No treatment has been established so far.

OBJECTIVE

We evaluated the safety and efficacy of oral supplementation of aceneuramic acid in patients with GNE myopathy.

METHODS

This multicenter, placebo-controlled, double-blind study comprised genetically confirmed GNE myopathy patients in Japan who were randomly assigned into treatment groups of sialic acid-extended release (SA-ER) tablets (6 g/day for 48 weeks) or placebo groups (4:1). The primary endpoint of effectiveness was set as the change in total upper limb muscle strength (upper extremity composite [UEC] score) from the start of administration to the final evaluation time point.

RESULTS

Among the 20 enrolled patients (SA-ER group, 16; placebo group, 4), 19 completed this 48-week study. The mean value of change in UEC score (95% confidence interval [CI]) at 48 weeks was -0.1 kg (-2.1 to 2.0) in the SA-ER group and -5.1 kg (-10.4 to 0.3) in the placebo group. The least squares mean difference (95% CI) between the groups in the covariance analysis was 4.8 kg (-0.3 to 9.9; P = 0.0635). The change in UEC score at 48 weeks was significantly higher in the SA-ER group compared with the placebo group (P = 0.0013) in the generalized estimating equation test repeated measurement analysis. In one patient in the SA-ER group, who was found to be pregnant 2 weeks after drug administration fetal death with tangled umbilical cord occurred at 13 weeks after the discontinuation of treatment. No other serious adverse effects were observed.

CONCLUSIONS

The present study indicates that oral administration of SA-ER tablets is effective and safe in patients with GNE myopathy in Japan.

Long-term evaluation parameters in GNE myopathy: a 5-year observational follow-up natural history study

Background

A number of clinical trials targeting GNE myopathy patients have been conducted. However, useful clinical parameters for postmarketing surveillance and long-term clinical observation have not yet been established.

Objective

We conducted a 5-year observational follow-up natural history study to identify evaluation parameters, which may be useful for the long-term observation of GNE myopathy patients.

Methods

Thirty-three genetically confirmed GNE myopathy patients were recruited and evaluated at study entry (baseline) and yearly in a 5-year follow-up. Hand-held dynamometer measurements of knee extension strength, grip power and pinch power, summed Manual Muscle Testing (MMT) score of 17 muscles, Gross Motor Function Measure (GMFM), 6 min walk test, percent vital capacity and percent forced vital capacity (%FVC), lean body mass (whole body, arms and legs), creatine kinase, Barthel Index, modified Rankin Scale and 36-item Short Form Survey national standard scores were examined.

Results

Of the 33 patients, 22 (66%) completed evaluations for the entire 5-year follow-up period. These patients had a significant reduction in summed MMT score (p=0.005), GMFM (p=0.005), pinch power (p<0.001) and %FVC (p<0.001) at the fifth year evaluation relative to baseline. Among these parameters, summed MMT score, GMFM, pinch power and %FVC showed significant changes even in non-ambulant patients.

Conclusions

MMT, GMFM, pinch power and %FVC are useful parameters for the long-term evaluation of GNE myopathy patients.

Recent advances in establishing a cure for GNE myopathy

PURPOSE OF REVIEW

GNE myopathy is a rare autosomal recessive disease caused by biallelic variants in the GNE gene, which encodes an enzyme involved in sialic acid biosynthesis. No drugs are approved for the treatment of GNE myopathy. Following proof-of-concept of sialic acid supplementation efficacy in mouse models, multiple clinical trials have been conducted. Here, we review clinical trials of sialic acid supplementation therapies and provide new insights into the additional clinical features of GNE myopathy.

RECENT FINDINGS

Clinical trials of sialic acid supplementation have been conducted in Europe, the USA, Japan, and South Korea. Some clinical trials of NeuAc-extended release tablets demonstrated amelioration of decline in upper extremity muscle strength; however, no significant improvement was observed in phase 3 trials in Europe and USA. A phase 2 trial of ManNAc showed slowed decline of both upper and lower extremity strength. GNE myopathy patient registries have been established in Europe and Japan, and have provided information on extramuscular manifestations such as thrombocytopenia, respiratory dysfunction, and sleep apnea syndrome. Sensitive and reliable biomarkers, and a disease-specific functional activity scale, have also been investigated.

SUMMARY

We discuss recent advances in establishing a GNE myopathy cure, and discuss other prospective therapeutic options, including gene therapy.

Role of HSP70 chaperone in protein aggregate phenomenon of GNE mutant cells: Therapeutic lead for GNE Myopathy

Limited treatment options and research in understanding the pathomechanisms of rare diseases has raised concerns about their therapeutic development. One such poorly understood ultra-rare neuromuscular disorder is GNE Myopathy (GNEM) which is caused due to mutation in key sialic acid biosynthetic enzyme, GNE. Treatment with sialic acid or its derivatives/precursors slows the disease progression, but curative strategies need to be explored further. Pathologically, muscle biopsy samples of GNEM patients reveal rimmed vacuole formation due to aggregation of β-amyloid, Tau, presenilin proteins with unknown mechanism. The present study aims to understand the mechanism of protein aggregate formation in GNE mutant cells to decipher role of chaperones in disease phenotype. The pathologically relevant GNE mutations expressed as recombinant proteins in HEK cells was used as a model system for GNEM to estimate extent of protein aggregation. We identified HSP70, a chaperone, as binding partner of GNE. Downregulation of HSP70 with altered BAG3, JNK, BAX expression levels was observed in GNE mutant cells. The cell apoptosis was observed in GNE mutation specific manner. An activator of HSP70 chaperone, BGP-15, rescued the phenotypic defects due to GNE mutation, thereby, reducing protein aggregation significantly. The results were further validated in rat skeletal muscle cell lines carrying single Gne allele. Our study suggests that HSP70 activators can be a promising therapeutic target in the treatment of ultra-rare GNE Myopathy disease.

Disease monitoring programs of rare genetic diseases: transparent data sharing between academic and commercial stakeholders

It has recently been suggested that registries for rare neuromuscular diseases should be formed and governed exclusively by physicians and patients in an effort to limit conflicts of interest. Enacting such an approach would not only be challenging logistically and financially, but it would also exclude the involvement of sponsors, who are an integral component of drug development within the current compliance framework. Therefore, as an alternative to traditional registries, we propose the use of a better collaborative model for post-marketing follow-up that includes all stakeholders. We developed the concept of Disease Monitoring Programs (DMPs), which are designed to monitor disease manifestations over a 10-year period whether on a sponsored drug or not, and ensure consistent collection, ownership sharing and governance of data.