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FXR1 is an alternatively spliced gene that encodes RNA binding proteins (FXR1P) involved in muscle development. In contrast to other tissues, cardiac and skeletal muscle express two FXR1P isoforms that incorporate an additional exon-15. We report that recessive mutations in this particular exon of FXR1 cause congenital multi-minicore myopathy in humans and mice. Additionally, we show that while Myf5 -dependent depletion of all FXR1P isoforms is neonatal lethal, mice carrying mutations in exon-15 display non-lethal myopathies which vary in severity depending on the specific effect of each mutation on the protein. FXR1P is a RNA binding protein involved in muscle development. Here, the authors show that mutations in FXR1 exon 15, which is alternatively spliced in muscle, cause multi-minicore myopathy in humans and in mouse models.

PurposeCongenital fibrosis of extraocular muscles type 1 (CFEOM1), a classical subtype of CFEOM, is characterized by restrictive ophthalmoplegia and ptosis. It is mainly caused by aberrant neural innervation of the extraocular muscles. This study aimed to investigate the genetic characteristics and clinical manifestations of CFEOM1 in Chinese families.MethodsThe clinical data, including ocular examinations, magnetic resonance imaging (MRI), and surgical procedures of affected individuals from 16 Chinese CFEOM1 families, were collected. The genomic DNA of 16 probands and their family members were sequenced for causative KIF21A gene mutations. Linkage analysis using microsatellite markers across KIF21A was also conducted.ResultsAffected individuals were presented with bilateral non-progressive ptosis, restricted horizontal eye movement, fixed infraduction of both eyes, compensatory chin-up head position, and neuromuscular abnormalities. Three heterozygous KIF21A mutations, c.2860C > T (p.R954W) (in eight families), c.2861G > T (p.R954L) (in two families), and c.2861G > A (p.R954Q) (in two families) were identified, which implied that hotspot mutations were common in Chinese CFEOM1 families. Germline Mosaicism was likely to be the cause of affected individuals with asymptomatic parents without KIF21A mutations presented in the eight families. Two affected individuals underwent modified levator muscle complex suspension surgery and achieved a good result without any complications.ConclusionInstead of evaluating the whole CFEOM1 gene variant, hotspot mutations could be given priority for screening. The occurrence of germline mosaicism has to be taken into account in genetic counseling. Patients with CFEOM1 who have ptosis may benefit from an innovative surgical procedure called modified levator muscle complex suspension.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is caused by pathogenic mutations in the nuclear TYMP gene, which encodes the cytosolic enzyme thymidine phosphorylase. In addition to the systemic accumulation of thymidine and deoxyuridine, several case studies have reported abnormalities in a range of other metabolites in patients with MNGIE. Since metabolites are intermediates or end-products of numerous biochemical reactions, they serve as highly informative indicators of an organism’s metabolic activity. This study aimed to perform an untargeted metabolomic profiling to determine whether individuals with MNGIE exhibit a distinct plasma metabolic signature compared to 15 age- and sex-matched healthy controls. Metabolites were profiled using Ultra-High-Performance Liquid Chromatography–Mass Spectrometry (UHPLC-MS). A total of 160 metabolites were found to be significantly upregulated and 260 downregulated in patients with MNGIE. KEGG pathway enrichment analysis revealed disruptions in 20 metabolic pathways, with arachidonic acid metabolism and bile acid biosynthesis being the most significantly upregulated. Univariate receiver operating characteristic (ROC) curve analyses identified 23 individual metabolites with diagnostic potential, each showing an area under the curve (AUC) ≥ 0.80. We propose that an impaired resolution of inflammation contributes to a chronic inflammatory state in MNGIE, potentially driving disease progression. Additionally, we suggest that the gut–liver axis plays a central role in MNGIE pathophysiology, with hepatic function being bidirectionally influenced by gut-derived factors.

Myogenic transcription factors with a basic helix–loop–helix (bHLH) such as MYOD, myogenin, MRF4, and MYF5 contribute to muscle differentiation and regulation. The MYF5 gene located on chromosome 12 encodes for myogenic factor 5 (MYF5), which has a role in skeletal and extraocular muscle development and rib formation. Variants in MYF5 were found to cause external ophthalmoplegia with rib and vertebral anomalies (EORVA), a rare recessive condition. To date, three homozygous variants in MYF5 have been reported to cause EORVA in six members of four unrelated families. Here, we present a novel homozygous MYF5 frameshift variant, c.596dupA p. (Asn199Lysfs*49), causing premature protein termination and presenting with external ophthalmoplegia, ptosis, and scoliosis in three siblings from a consanguineous family of Pakistani origin. With four MYF5 variants now discovered, genetic testing and paediatric assessment for extra-ocular features should be considered in all cases of congenital ophthalmoplegia.

Inherited deficiency of thymidine phosphorylase (TP), encoded by TYMP , leads to a rare disease with multiple mitochondrial DNA (mtDNA) abnormalities, mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). However, the impact of TP deficiency on lysosomes remains unclear, which are important for mitochondrial quality control and nucleic acid metabolism. Muscle biopsy tissue and skin fibroblasts from MNGIE patients, patients with m.3243 A > G mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) and healthy controls (HC) were collected to perform mitochondrial and lysosomal functional analyses. In addition to mtDNA abnormalities, compared to controls distinctively reduced expression of LAMP1 and increased mitochondrial content were detected in the muscle tissue of MNGIE patients. Skin fibroblasts from MNGIE patients showed decreased expression of LAMP2, lowered lysosomal acidity, reduced enzyme activity and impaired protein degradation ability. TYMP knockout or TP inhibition in cells can also induce the similar lysosomal dysfunction. Using lysosome immunoprecipitation (Lyso- IP), increased mitochondrial proteins, decreased vesicular proteins and V-ATPase enzymes, and accumulation of various nucleosides were detected in lysosomes with TP deficiency. Treatment of cells with high concentrations of dThd and dUrd also triggers lysosomal dysfunction and disruption of mitochondrial homeostasis. Therefore, the results provided evidence that TP deficiency leads to nucleoside accumulation in lysosomes and lysosomal dysfunction, revealing the widespread disruption of organelles underlying MNGIE. Graphical Abstract

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a multi-system disorder caused by several homozygous or compound heterozygous mutations, mostly in the nuclear gene of TYMP. Our current knowledge on the underlying pathology of the disease is derived through the study of about 200 cases of different ethnicities. Clinical presentations include severe cachexia, weakness, ptosis, diplopia, abdominal cramps or digestive tract disorders, hearing impairment, and paresthesia.Herein, we aim to present five novel mutations of the nuclear gene of TYMP in six Iranian patients diagnosed with MNGIE. In our population, age at the time of diagnosis was 18 to 49 years, while the onset of the symptoms varied from 13 to 20 years. We detected two pathogenic non-frameshift nonsense premature stop codon mutations (c.1013C > A, and c.130C > T), one variant of uncertain significance (VUS) non-frameshift missense mutation (c.345G > T), one likely pathogenic frameshift insertion (c.801_802insCGCG), and one likely benign homozygous non-frameshift deletion (c.1176_1187del) from two siblings. Our findings also confirm the autosomal recessive inheritance pattern of MNGIE in the Iranian population. The lack of knowledge in the area of nuclear gene-modifier genes shadows the genotype–phenotype relationships of MNGIE.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) syndrome is an extremely rare multisystem disorder with autosomal recessive inheritance and impairs mitochondrial DNA replication, which causes myopathy and neurodegeneration. The classical symptoms of this syndrome are progressive gastrointestinal dysmotility and peripheral neuropathy. We are presenting a patient who had MNGIE syndrome and presented with anejaculation for the first time in the literature. A 27-year-old male patient applied to the urology clinic with anejaculation. It was learned that the patient had lifelong anejaculation and had no problems with libido, erection, or orgasm from his sexual history. In the evaluation of the etiology of anejaculation, the patient did not have any known causes of anejaculation. From the patient’s medical history, it was learned that he was diagnosed with MNGIE syndrome when he presented to another hospital with gastrointestinal symptoms 5 years ago. Neurodegenerative diseases are the potential cause of anejaculation due to sensorimotor neuropathy and paresthesia. The patient was given genetic counseling and was informed about assisted reproductive techniques and that his partner should be screened for MNGIE syndrome. In conclusion, when evaluating neurodegenerative diseases, it is of great importance to question the patients’ sexual problems, which are important for their quality of life, and to provide appropriate counseling.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an ultra-rare disease for which there are currently no validated outcome measures for assessing therapeutic intervention efficacy. The aim of this study was to identify a plasma and/or serum microRNA (miRNA) biomarker panel for MNGIE. Sixty-five patients and 65 age and sex matched healthy controls were recruited and assigned to one of four study phases: (i) discovery for sample size determination; (ii) candidate screening; (iii) candidate validation; and (iv) verifying the performance of the validated miRNA panel in four patients treated with erythrocyte-encapsulated thymidine phosphorylase (EE-TP), an enzyme replacement under development for MNGIE. Quantitative PCR (qPCR) was used to profile miRNAs in serum and/or plasma samples collected for the discovery, validation and performance phases, and next generation sequencing (NGS) analysis was applied to serum samples assigned to the candidate screening phase. Forty-one differentially expressed candidate miRNAs were identified in the sera of patients (p < 0.05, log2 fold change > 1). The validation cohort revealed that of those, 27 miRNAs were upregulated in plasma and three miRNAs were upregulated in sera (p < 0.05). Through binary logistic regression analyses, five plasma miRNAs (miR-192-5p, miR-193a-5p, miR-194-5p, miR-215-5p and miR-34a-5p) and three serum miRNAs (miR-192-5p, miR-194-5p and miR-34a-5p) were shown to robustly distinguish MNGIE from healthy controls. Reduced longitudinal miRNA expression of miR-34a-5p was observed in all four patients treated with EE-TP and coincided with biochemical and clinical improvements. We recommend the inclusion of the plasma exploratory miRNA biomarker panel in future clinical trials of investigational therapies for MNGIE; it may have prognostic value for assessing clinical status.

Background Mitochondrial neurogastrointestinal encephalopathy (MNGIE) is a rare autosomal recessive disorder caused by variants in the TYMP gene, which encodes thymidine phosphorylase (TP). It is characterized by multisystem involvement, with prominent gastrointestinal, neurological, and systemic manifestations that typically exhibit progressive worsening over time. Methods We characterized a multigenerational MNGIE family through comprehensive proband analysis, identifying compound heterozygous TYMP variants (c.131G > C, p.Arg44Pro and c.1268T>G, p.Leu423Arg in trans) as the molecular basis of disease. Extended family testing for genetic counseling confirmed no secondary pathogenic variants. Muscle biopsies were analyzed using comprehensive staining techniques. Genomic analysis involved next-generation sequencing (NGS) of the proband’s DNA and Sanger sequencing of family members’ DNA to confirm variants. In silico analysis utilized bioinformatics tools and protein modeling to predict pathogenicity and assess structural impacts, with variant classification adhering to American College of Medical Genetics and Genomics(ACMG) guidelines. Additionally, a literature review of Chinese MNGIE cases was conducted to contextualize the findings. Results The proband exhibited characteristic MNGIE features, including gastrointestinal dysmotility, diffuse leukoencephalopathy on brain MRI (magnetic resonance imaging), and electrophysiologically confirmed peripheral neuropathy. Muscle biopsy revealed ragged red fibers, cytochrome c oxidase-deficient fibers, and enhanced succinate dehydrogenase activity in blood vessels, consistent with mitochondrial dysfunction. Genetic analysis identified a novel TYMP variant (c.1268T > G, p.Leu423Arg) and a known variant (c.131G > C, p.Arg44Pro) in the proband, both classified as likely pathogenic according to ACMG guidelines. Molecular analysis of other 11 family members detected heterozygous carriers of either the c.1268T > G or c.131G > C variant in six asymptomatic individuals. In silico analysis confirmed that both variants are highly conserved and likely pathogenic. Protein modeling revealed that both variants compromise structural integrity and conformation, impairing TP function. Homozygous or compound heterozygous missense variants were identified as the predominant genetic alterations in 16 Chinese MNGIE cases, with gastrointestinal and neurological symptoms being the most common clinical manifestations. Conclusions This study enriches the variant spectrum in Chinese patients, highlights the importance of early diagnosis prior to the onset of cachexia and irreversible tissue damage, and enhances the understanding of genetic heterogeneity.

Purpose Mitochondrial DNA (mtDNA) depletion syndrome (MDDS) encompasses a group of genetic disorders of mtDNA maintenance. Mutation of RRM2B is an uncommon cause of infantile-onset encephalomyopathic MDDS. Here we describe the natural history of this disease. Methods Multinational series of new genetically confirmed cases from six pediatric centers. Results Nine new cases of infantile-onset RRM2B deficiency, and 22 previously published cases comprised a total cohort of 31 patients. Infants presented at a mean of 1.95 months with truncal hypotonia, generalized weakness, and faltering growth. Seizures evolved in 39% at a mean of 3.1 months. Non-neurological manifestations included respiratory distress/failure (58%), renal tubulopathy (55%), sensorineural hearing loss (36%), gastrointestinal disturbance (32%), eye abnormalities (13%), and anemia (13%). Laboratory features included elevated lactate (blood, cerebrospinal fluid (CSF), urine, magnetic resonance (MR), spectroscopy), ragged-red and cytochrome c oxidase–deficient fibers, lipid myopathy, and multiple oxidative phosphorylation enzyme deficiencies in skeletal muscle. Eight new RRM2B variants were identified. Patients with biallelic truncating variants had the worst survival. Overall survival was 29% at 6 months and 16% at 1 year. Conclusions Infantile-onset MDDS due to RRM2B deficiency is a severe disorder with characteristic clinical features and extremely poor prognosis. Presently management is supportive as there is no effective treatment. Novel treatments are urgently needed.