GNE Gene Research Articles

Novel variants and genotype-phenotype correlation in a multicentre cohort of GNE myopathy in China

BackgroundGlcNAc2-epimerase (GNE) myopathy is a rare autosomal recessive disorder caused by pathogenic variants in the GNE gene, which is essential for the sialic acid biosynthesis pathway.ObjectiveThis multi-centre study aimed to...

Human induced pluripotent stem cell line (FDHSi005-A) derived from a patient with a deep intronic variant in the GNE gene

GlcNAc2-epimerase myopathy is a rare autosomal recessive myopathy characterized by distal involvement in the lower extremities. Our study reprogrammed human-induced pluripotent stem cells from peripheral blood mononuclear cells of a patient with GNE gene deep intronic variant c.862 + 870C>T and c.478C>T compound heterozygous mutations that co-segregated with the disease. The generated iPSCs express pluripotent cell markers with no mycoplasma contamination. Additionally, these iPSCs demonstrated pluripotency, the capacity to differentiate into the three germ layers, and maintained normal karyotypes. Importantly, we identified that these iPSCs possess the same specific mutations as the patient, making them a robust model for studying GNE myopathy and developing potential therapeutic interventions.

Induced Muscle and Liver Absence of Gne in Postnatal Mice Does Not Result in Structural or Functional Muscle Impairment.

GNE Myopathy is a unique recessive neuromuscular disorder characterized by adult-onset, slowly progressive distal and proximal muscle weakness, caused by mutations in the GNE gene which is a key enzyme in the biosynthesis of sialic acid. To date, the precise pathophysiology of the disease is not well understood and no reliable animal model is available. Gne KO is embryonically lethal in mice. To gain insights into GNE function in muscle, we have generated an inducible muscle Gne KO mouse. To minimize the contribution of the liver to the availability of sialic acid to muscle via the serum, we have also induced combined Gne KO in liver and muscle. A mouse carrying loxp sequences flanking Gne exon3 was generated by Crispr/Cas9 and bred with a human skeletal actin (HSA) promoter driven CreERT mouse. Gne muscle knock out was induced by tamoxifen injection of the resulting homozygote GneloxpEx3loxp/HSA Cre mouse. Liver Gne KO was induced by systemic injection of AAV8 vectors carrying the Cre gene driven by the hepatic specific promoter of the thyroxine binding globulin gene. Characterization of these mice for a 12 months period showed no significant changes in their general behaviour, motor performance, muscle mass and structure in spite of a dramatic reduction in sialic acid content in both muscle and liver. We conclude that post weaning lack of Gne and sialic acid in muscle and liver have no pathologic effect in adult mice. These findings could reflect a strong interspecies versatility, but also raise questions about the loss of function hypothesis in Gne Myopathy. If these findings apply to humans they have a major impact on therapeutic strategies.

A novel variant in the GNE gene in a Malian patient presenting with distal myopathy.

GNE-myopathy (GNE-M) is a rare autosomal recessive disorder caused by variants in the GNE gene. We report a novel variant in GNE causing GNE-M in a Malian family. A 19-year-old male patient from consanguineous marriage was seen for progressive walking difficulty. Neurological examination found predominant distal muscle weakness and atrophy, decreased tendon reflexes, predominating in lower limbs. Electroneuromyography showed an axonal neuropathy pattern. However, whole exome sequencing (WES) revealed a novel biallelic variant in GNE c.1838G > A:p.Gly613Glu, segregating with the phenotype within the family. This study highlights its diagnosis challenges in sub-Saharan Africa and broadens the genetic spectrum of this rare disease.

A novel mutation alters GNE bifunctional enzyme activity and leads to familial inherited GNE diseases

Distal myopathies are a group of rare heterogeneous diseases that are mostly caused by genetic factors. At least 20 genes have been associated with distal myopathies. We performed whole-exome sequencing to identify the genetic cause of disease in a family with distal myopathy. Following the American College of Medical Genetics and Genomics (ACMG) guidelines, we analyzed the sequencing results and screened suspicious mutations based on mutation frequency, functional impact, and disease inheritance pattern. The harmfulness of the mutations was predicted using bioinformatics methods, and the pathogenic mutations were determined. We identified a novel amino acid mutation (NP_005467.1:p.S663L) on the GNE gene that may cause familial distal myopathy. This mutation is the result of the simultaneous mutation of two adjacent nucleotides (c.1988C > T, c.1989C > A) in the codon. First, we measured the mRNA and protein expression of the GNE gene in the lymphoblastoid cell lines (LCLs) of the probands and their family members. Second, GNE vectors carrying the novel mutation, two other known pathogenic mutations, and the wild-type gene were constructed and transfected into HEK293T cells. The enzymatic activity of these GNE variants was investigated and showed that the p.S663L mutation significantly reduced the activity of the bifunctional GNE enzyme without altering the expression level of the GNE protein. Furthermore, the mutation may also alter the immunogenicity of the 3′ end of the GNE protein, potentially affecting its oligomer formation. In this study, a novel GNE gene mutation that may cause distal myopathy was identified, expanding the spectrum of genetic mutations associated with this disease.

Large phenotypic diversity by genotype in patients with GNE myopathy: 10years after the establishment of a national registry in Japan.

GNE myopathy is an ultra-rare autosomal recessive distal myopathy caused by pathogenic variants of the GNE gene, which encodes a key enzyme in sialic acid biosynthesis. The present study aimed to examine the long-term progression of GNE myopathy, genotype-phenotype correlations, and complications to provide useful information for predicting patient progression and designing clinical trials using a large collection of registry data over a 10-year period. We analyzed 220 Japanese patients with GNE myopathy from a national registry in Japan. Diagnoses were confirmed by genetic curators based on genetic analysis reports. We analyzed registration sheets and annually updated items completed by attending physicians. In total, 197 of 220 participants (89.5%) carried p.D207V or p.V603L in at least one allele. The median disease duration to loss of ambulation was estimated to be 10 years in p.V603L homozygotes (n = 48), whereas more than 90% of p.D207V/p.V603L compound heterozygotes were estimated to be ambulatory even 20 years after disease onset according to Kaplan-Meier analysis (p < 0.001). Moreover, participants with a younger age of onset lost ambulation earlier regardless of genotype. A decline in respiratory function was observed as the disease progressed, particularly in p.V603L homozygotes, whereas none of the p.D207V/p.V603L compound heterozygotes showed a decline. The present study demonstrated large differences in disease progression and respiratory function between genotypes. Moreover, age of onset was found to be an indicator of disease severity regardless of genotype in GNE myopathy patients. These results may help stratify patients in clinical trials and predict disease progression.

Recessive GNE Mutations in Korean Nonaka Distal Myopathy Patients with or without Peripheral Neuropathy.

Autosomal recessive Nonaka distal myopathy is a rare autosomal recessive genetic disease characterized by progressive degeneration of the distal muscles, causing muscle weakness and decreased grip strength. It is primarily associated with mutations in the GNE gene, which encodes a key enzyme of sialic acid biosynthesis (UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase). This study was performed to find GNE mutations in six independent distal myopathy patients with or without peripheral neuropathy using whole-exome sequencing (WES). In silico pathogenic prediction and simulation of 3D structural changes were performed for the mutant GNE proteins. As a result, we identified five pathogenic or likely pathogenic missense variants: c.86T>C (p.Met29Thr), c.527A>T (p.Asp176Val), c.782T>C (p.Met261Thr), c.1714G>C (p.Val572Leu), and c.1771G>A (p.Ala591Thr). Five affected individuals showed compound heterozygous mutations, while only one patient revealed a homozygous mutation. Two patients revealed unreported combinations of combined heterozygous mutations. We observed some specific clinical features, such as complex phenotypes of distal myopathy with distal hereditary peripheral neuropathy, an earlier onset of weakness in legs than that of hands, and clinical heterogeneity between two patients with the same set of compound heterozygous mutations. Our findings on these genetic causes expand the clinical spectrum associated with the GNE mutations and can help prepare therapeutic strategies.

Pseudoexon activation by deep intronic variation in GNE myopathy with thrombocytopenia.

GNE myopathy is a rare autosomal recessive disorder caused by pathogenic variants in the GNE gene, which is essential for the sialic acid biosynthesis pathway. Although over 300 GNE variants have been reported, some patients remain undiagnosed with monoallelic pathogenic variants. This study aims to analyze the entire GNE genomic region to identify novel pathogenic variants. Patients with clinically compatible GNE myopathy and monoallelic pathogenic variants in the GNE gene were enrolled. The other GNE pathogenic variant was verified using comprehensive methods including exon 2 quantitative polymerase chain reaction and nanopore long-read single-molecule sequencing (LRS). A deep intronic GNE variant, c.862+870C>T, was identified in nine patients from eight unrelated families. This variant generates a cryptic splice site, resulting in the activation of a novel pseudoexon between exons 5 and 6. It results in the insertion of an extra 146 nucleotides into the messengerRNA (mRNA), which is predicted to result in a truncated humanGNE1(hGNE1) protein. Peanut agglutinin（PNA） lectin staining of muscle tissues showed reduced sialylation of mucin O-glycans on sarcolemmal glycoproteins. Notably, a third of patients with the c.862+870C>T variant exhibited thrombocytopenia. A common core haplotype harboring the deep intronic GNE variant was found in all these patients. The transcript with pseudoexon activation potentially affects sialic acid biosynthesis via nonsense-mediated mRNA decay, or resulting in a truncated hGNE1 protein, which interferes with normal enzyme function. LRS is expected to be more frequently incorporated in genetic analysis given its efficacy in detecting hard-to-find pathogenic variants.

Preserved Forearm and Hand Muscles and Diaphragm with Mild Cardiac and Respiratory Involvement in a Patient with GNE Myopathy Harboring Homozygous Variants in GNE (c.1807G>C, p.V603L) over Four Decades after the Onset.

We encountered a 67-year-old Japanese man with GNE myopathy and homozygous variants (c.1807G>C, p.V603L) of the GNE gene. The patient developed weakness in the left foot at 24 years old and could only move his wrist joints and hands 43 years after the onset. This genotype is the most common variant and causes severe muscle involvement; however, the distal upper extremities are preserved until the end-stage of the disease. Although severe heart failure is rare in GNE myopathy, mild cardiac dysfunction (ejection fraction 46.1%) was observed. Furthermore, respiratory dysfunction was noted with a preserved diaphragm.

Wolman’s Disease and GNE Myopathy Frequency to Religion

Complete absence or deficiency of Lysosomal acid lipase (LAL) leads to the rare infantile disorder Wolman's Disease [1]. Decreased function of GNE can lead to GNE myopathy [2]. Although both pathological phenotypes are rare, LAL deficiency only affects 1 in every 500,000 births and dysfunction of GNE affects 1 in every 1,000,000 births, there is a higher incidence in the religious groups of the Middle East; the incidence is projected to be as high as 1 in every 4,200 births [3,4]. The LIPA gene encodes for LAL while the GNE gene encodes for UDPN- acetylglucosamine (GlcNAc) 2-epimerase/N-acetylmannosamine (ManNAc) kinase [4,5]. LAL catalyzes the hydrolysis of cholesterol esters and triglycerides [6]. GlcNAc and ManNAc are responsible for the biosynthesis of sialic acid [7]. Presence of variations in GNE genes are known to impair the enzymes and lead to pathological phenotypes. This study reports the prevalence of mutations c.260G&gt;T; p.G87V and c.894G&gt;A; E8SJM in the lipase gene (LIPA) and c.2228T&gt;C p.M743T in GNE gene amongst different religions. We sequenced 1,354 samples for the presence of the variations in LIPA exon 4 and 8 along with GNE exon 13(formerly exon 12). The sample population comprised individuals of varying Middle Eastern religions such as Mizrahi Jewish, Muslims, Christians, Baha’i, Catholic, Buddhist and Zoroastrian. The other religions that were not Mizrahi Jewish were classified under “Non-Jewish” to have a more even distribution. LIPA gene exon 4 variation p.G87V had a heterozygous frequency of 22 in 1,354(1.62%) with 20 of 22(90.9%) heterozygotes being Mizrahi Jewish while 2 of 22(9.09%) heterozygotes were Non-Jewish. Exon 8 splice junction mutation E8SJM, G&gt;A transition at position 1 had a frequency of 2 in 1,354 (0.14%) with 2 of 2(100%) heterozygotes being Mizrahi Jewish. GNE exon 13 variation p.M743T (formerly exon 12 p.M712T) had a mutation frequency of 58 in 1,354(4.28%) with 5 of these 58(8.62%) samples being homozygous while 53 of the 58(91.37%) were heterozygous. In 58 samples that yielded a mutation, 54 of them were Mizarhi jewish (93.1%).

Evaluation of N-Acetylmannosamine Administration to Restore Sialylation in GNE-Deficient Human Embryonal Kidney Cells.

A key mechanism in the neuromuscular disease GNE myopathy (GNEM) is believed to be that point mutations in the GNE gene impair sialic acid synthesis - maybe due to UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) activity restrictions - and resulting in muscle tissue loss. N-acetylmannosamine (ManNAc) is the first product of the bifunctional GNE enzyme and can therefore be regarded as a precursor of sialic acids. This study investigates whether this is also a suitable substance for restoring the sialic acid content in GNE-deficient cells. A HEK-293 GNE-knockout cell line was generated using CRISPR-Cas9 and analyzed for its ability to synthesize sialic acids. The cells were then supplemented with ManNAc to compensate for possible GNE inactivity and thereby restore sialic acid synthesis. Sialic acid levels were monitored by immunoblot and high performance liquid chromatography (HPLC). The HEK-293 GNE-knockout cells showed almost no polysialylation signal (immunoblot) and a reduced overall (-71%) N-acetylneuraminic acid (Neu5Ac) level (HPLC) relative to total protein and normalized to wild type level. Supplementation of GNE-deficient HEK-293 cells with 2 mM ManNAc can restore polysialylation and free intracellular sialic acid levels to wild type levels. The addition of 1 mM ManNAc is sufficient to restore the membrane-bound sialic acid level. Although the mechanism behind this needs further investigation and although it remains unclear why adding ManNAc to GNE-deficient cells is sufficient to elevate polysialylation back to wild type levels - since this substance is also converted by the GNE, all of this might yet prove helpful in the development of an appropriate therapy for GNEM.

Treatment and Follow-up Data for Young Patients with a Gne Defect and Congenital Thrombocytopenia

Congenital thrombocytopenia can be associated not only with a reduced production, but also with an accelerated degradation of platelets. Sialic acid binds to platelet surface glycoproteins and protects platelets from degradation via the Ashwell-Morell receptor. The GNE gene encodes an enzyme that initiates and regulates the biosynthesis of N-acetylneuraminic acid, a precursor of sialic acids. According to OMIM alterations in GNE are autosomal recessive associated with adult-onset progressive GNE myopathy (with or without thrombocytopenia) and autosomal dominant with sialuria. In recent years, biallelic GNE mutations located mainly in the N-acetylmannosamine (ManNAc) kinase domain of GNE have been described in children/young adults with otherwise unexplained thrombocytopenia. Recently, we identified compound heterozygous GNE variants in a young girl (Pt.1) with life-threatening intracranial bleeding and severe congenital thrombocytopenia (lowest platelet count 5 x 10 9/L), who needed weekly platelet transfusions. We showed decreased α2,3 sialic acid and increased terminal galactose and α2,6 sialic acid moieties in the girl´s platelets. She received hematopoietic stem cell transplantation (HSCT) at 2,3 years, which normalized platelet counts and function. Follow-up data showed normalized platelet function (20 months after HSCT) and counts (20, 21, and 23 months after HSCT). Following HSCT, the platelet lectin profile was markedly different from before transplantation with an increase in α2,3 sialic acid recognizing lectins WGA and MAL I compared with data before transplantation, indicating that sialic acid moieties have been normalized. Additionally, we identified a biallelic GNE variant in two siblings (Pt.2 and Pt.3) affected by congenital thrombocytopenia. Pt.2 is a 1,8-year-old boy with thrombocytopenia since birth (lowest platelet count 6 x10 9/L) who needed weekly platelet transfusions. His 17-year-old sister (Pt.3) presented with lifelong thrombocytopenia and suspected chronic immune thrombocytopenia; however, therapy with immunoglobulin and steroids did not elevate the platelets. The parents and two other siblings were clinically not affected. Flow cytometry performed for the affected siblings showed severely decreased thrombin-induced platelet CD62 and CD63 exposure hinting at an impaired α- and δ-granule secretion. NGS identified a homozygous GNE variant (NM_001128227.3:c.1727G&amp;gt;C, p.Gly576Ala) with damaging prediction to be present in both siblings. The parents and two healthy siblings are heterozygous carriers of this variant. The nucleotide change c.1726G&amp;gt;C leading to Gly576Arg has been described compound heterozygous in a patient with GNE myopathy. For the sister (Pt.3) lectin binding analysis showed decreased α-2,3 sialylation (MAA) and increased terminal galactose (RCA120) expression on platelets. This pattern is consistent with loss of sialic acid synthesis and indicative of rapid platelet clearance. She had received therapy with romiplostim since she was 12, resulting in stable platelet counts (&amp;gt; 50 x10 9/L). At the age of 1 year, Pt.2 also started with romiplostim therapy. During the 8-month treatment, platelet counts were mainly stable above 30 x 10 9/L. Only two transfusions were necessary when platelet counts dropped to 18 and 11 x 10 9/L. In conclusion, this research elucidates novel associations between GNE mutations, specifically within the ManNAc kinase domain, and congenital thrombocytopenia. These findings were derived from studying three patients carrying such mutations, underscoring this discovery's potential broad relevance. Importantly, this alteration in the GNE gene, traditionally associated with GNE myopathy, prompts us to anticipate and closely monitor the potential future development of this neuromuscular condition in these patients. Of particular interest is the effectiveness of romiplostim in ameliorating thrombocytopenia in these cases. Both siblings in our study exhibited stable, acceptable platelet counts in response to this therapy, suggesting that romiplostim might offer a promising therapeutic strategy for managing congenital thrombocytopenia linked to GNE mutations.

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 of Aceneuramic Acid for Distal Myopathy with Rimmed Vacuoles

Distal myopathy with rimmed vacuoles (DMRV), also known as GNE myopathy, is a rare disease affecting the distal muscles, such as the tibialis anterior muscle. The GNE gene, which codes for a key enzyme in the sialic acid biosynthesis pathway, is mutated in a homozygous or compound heterozygous manner, and the lack of sialic acid in skeletal muscle is the critical underlying mechanism in DMRV pathogenesis. DMRV mouse models were established, and supplementation with sialic acid improved the phenotypes of the models. A phase 1 clinical trial using aceneuramic acid was conducted at Tohoku University Hospital, Japan, followed by trials using a slow-release product. A phase II/III study, subsequent extended trial, and confirmatory trial were also conducted. Regulatory approval is currently under review.

PB0357 Hereditary Thrombocytopenia with Platelet Sialic Acid Deficiency and Mutations in the GNE Genes

PB0357 Hereditary Thrombocytopenia with Platelet Sialic Acid Deficiency and Mutations in the GNE Genes

Development of Assays to Measure GNE Gene Potency and Gene Replacement in Skeletal Muscle.

GNE myopathy (GNEM) is a severe muscle disease caused by mutations in the UDP-GlcNAc-2-epimerase/ManNAc-6-kinase (GNE) gene, which encodes a bifunctional enzyme required for sialic acid (Sia) biosynthesis. To develop assays to demonstrate the potency of AAV gene therapy vectors in making Sia and to define the dose required for replacement of endogenous mouse Gne gene expression with human GNE in skeletal muscles. A MyoD-inducible Gne-deficient cell line, Lec3MyoDI, and a GNE-deficient human muscle cell line, were made and tested to define the potency of various AAV vectors to increase binding of Sia-specific lectins, including MAA and SNA. qPCR and qRT-PCR methods were used to quantify AAV biodistribution and GNE gene expression after intravenous delivery of AAV vectors designed with different promoters in wild-type mice. Lec3 cells showed a strong deficit in MAA binding, while GNE-/-MB135 cells did not. Overexpressing GNE in Lec3 and Lec3MyoDI cells by AAV infection stimulated MAA binding in a dose-dependent manner. Use of a constitutive promoter, CMV, showed higher induction of MAA binding than use of muscle-specific promoters (MCK, MHCK7). rAAVrh74.CMV.GNE stimulated human GNE expression in muscles at levels equivalent to endogenous mouse Gne at a dose of 1×1013vg/kg, while AAVs with muscle-specific promoters required higher doses. AAV biodistribution in skeletal muscles trended higher when CMV was used as the promoter, and this correlated with increased sialylation of its viral capsid. Lec3 and Lec3MyoDI cells work well to assay the potency of AAV vectors in making Sia. Systemic delivery of rAAVrh74.CMV.GNE can deliver GNE gene replacement to skeletal muscles at doses that do not overwhelm non-muscle tissues, suggesting that AAV vectors that drive constitutive organ expression could be used to treat GNEM.

GNE myopathy: can homozygous asymptomatic subjects give a clue for the identification of protective factors?

GNE myopathy is caused by bi allelic recessive mutations in the GNE gene. The largest identified cohort of GNE myopathy patients carries a homozygous mutation- M743T (the “Middle Eastern” mutation). More than 160 such patients in 67 families have been identified by us. Mean onset in this cohort is 30 years (range 17–48) with variable disease severity. However, we have identified two asymptomatic females, homozygous for M743T in two different families, both with affected siblings. The first showed no myopathy when examined at age 76 years. The second has no sign of disease at age 60 years. Since both agreed only for testing of blood, we performed exome and RNA sequencing of their blood and that of their affected siblings. Various filtering layers resulted in 2723 variant loci between symptomatic and asymptomatic individuals, representing 1364 genes. Among those, 39 genes are known to be involved in neuromuscular diseases, and only in two of them the variant is located in the proper exon coding region, resulting in a missense change. Surprisingly, only 27 genes were significantly differentially expressed between the asymptomatic and the GNE myopathy affected individuals, with three overexpressed genes overlapping between exome and RNA sequencing. Although unable to unravel robust candidate genes, mostly because of the very low number of asymptomatic individuals analyzed, and because of the tissue analyzed (blood and not muscle), this study resulted in relatively restricted potential candidate protective genes, emphasizing the power of using polarized phenotypes (completely asymptomatic vs clearly affected individuals) with the same genotype to unmask those genes which could be used as targets for disease course modifiers.

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

BackgroundA 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.MethodsWe 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.ResultsA 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.ConclusionsThe 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).

Bialelic Pathogenic (c.830G&gt;A(p.R277Q)) Variant Disrupting the GNE Gene Function and Causes Nonaka myopathy Phenotype

Bialelic Pathogenic (c.830G&gt;A(p.R277Q)) Variant Disrupting the GNE Gene Function and Causes Nonaka myopathy Phenotype

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

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. We evaluated the safety and efficacy of oral supplementation of aceneuramic acid in patients with GNE myopathy. 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. 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. The present study indicates that oral administration of SA-ER tablets is effective and safe in patients with GNE myopathy in Japan.