Identification of a Novel Frameshift Variant in MYF5 Leading to External Ophthalmoplegia with Rib and Vertebral Anomalies.

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.

COQ7 defect causes prenatal onset of mitochondrial CoQ10 deficiency with cardiomyopathy and gastrointestinal obstruction.

COQ7 pathogenetic variants cause primary CoQ10 deficiency and a clinical phenotype of encephalopathy, peripheral neuropathy, or multisystemic disorder. Early diagnosis is essential for promptly starting CoQ10 supplementation. Here, we report novel compound heterozygous variants in the COQ7 gene responsible for a prenatal onset (20 weeks of gestation) of hypertrophic cardiomyopathy and intestinal dysmotility in a Bangladesh consanguineous family with two affected siblings. The main clinical findings were dysmorphisms, recurrent intestinal occlusions that required ileostomy, left ventricular non-compaction cardiomyopathy, ascending aorta dilation, arterial hypertension, renal dysfunction, diffuse skin desquamation, axial hypotonia, neurodevelopmental delay, and growth retardation. Exome sequencing revealed compound heterozygous rare variants in the COQ7 gene, c.613_617delGCCGGinsCAT (p.Ala205HisfsTer48) and c.403A>G (p.Met135Val). In silico analysis and functional in vitro studies confirmed the pathogenicity of the variants responsible for abolished activities of complexes I + III and II + III in muscle homogenate, severe decrease of CoQ10 levels, and reduced basal and maximal respiration in patients' fibroblasts. The first proband deceased at 14 months of age, whereas supplementation with a high dose of CoQ10 (30 mg/kg/day) since the first days of life modified the clinical course in the second child, showing a recovery of milestones acquirement at the last follow-up (18 months of age). Our study expands the clinical spectrum of primary CoQ10 deficiency due to COQ7 gene defects and highlights the essential role of multidisciplinary and combined approaches for a timely diagnosis.

Oculomasticatory rhythmic movements, insomnia and stroke-like episodes in a patient with POLG mutation.

The POLG mutation, a leading cause of mitochondrial diseases, exhibits a wide-ranging age of onset and a complex clinical presentation. We encountered an atypical clinical profile in an elderly man with a POLG mutation, characterised by a stroke-like episode, chronic insomnia and transient oculomasticatory rhythmic movement. History revealed chronic constipation since his 50s and progressive bilateral ophthalmoplegia since his early 60s. Subsequently, he had experienced acute encephalopathy and later developed chronic insomnia. The present neurological examination showed bilateral complete ophthalmoplegia, ptosis, and rhythmic ocular and jaw movements. Imaging indicated findings suggestive of a stroke-like episode and eventual genetic analysis revealed a homozygous missense mutation in the POLG gene. This case expands the clinical spectrum of POLG mutations in individuals over 60 years, showcasing the rare combination of a stroke-like episode, chronic insomnia and oculomasticatory rhythmic movement.

Tubulin CFEOM mutations both inhibit or activate kinesin motor activity.

Kinesin-mediated transport along microtubules is critical for axon development and health. Mutations in the kinesin Kif21a, or the microtubule subunit ß-tubulin, inhibit axon growth and/or maintenance resulting in the eye-movement disorder congenital fibrosis of the extraocular muscles (CFEOM). While most examined CFEOM-causing ß-tubulin mutations inhibit kinesin-microtubule interactions, Kif21a mutations activate the motor protein. These contrasting observations have led to opposed models of inhibited or hyperactive Kif21a in CFEOM. We show that, contrary to other CFEOM-causing ß-tubulin mutations, R380C enhances kinesin activity. Expression of ß-tubulin-R380C increases kinesin-mediated peroxisome transport in S2 cells. The binding frequency, percent motile engagements, run length and plus-end dwell time of Kif21a are also elevated on ß-tubulin-R380C compared with wildtype microtubules in vitro. This conserved effect persists across tubulins from multiple species and kinesins from different families. The enhanced activity is independent of tail-mediated kinesin autoinhibition and thus utilizes a mechanism distinct from CFEOM-causing Kif21a mutations. Using molecular dynamics, we visualize how ß-tubulin-R380C allosterically alters critical structural elements within the kinesin motor domain, suggesting a basis for the enhanced motility. These findings resolve the disparate models and confirm that inhibited or increased kinesin activity can both contribute to CFEOM. They also demonstrate the microtubule's role in regulating kinesins and highlight the importance of balanced transport for cellular and organismal health.

The clinical, myopathological, and genetic analysis of 155 Chinese mitochondrial ophthalmoplegia patients with mitochondrial DNA single large deletions.

BACKGROUND: Progressive external ophthalmoplegia (PEO) is a common subtype of mitochondrial encephalomyopathy. OBJECTIVE: The study aimed to investigate the relationship between mitochondrial DNA (mtDNA) abnormalities, muscle pathology, and clinical manifestations in Chinese patients with single large-scale mtDNA deletion presenting with PEO. METHODS: This is a retrospective single-center study. Patients with PEO who had a single large deletion in mitochondrial DNA were included in this study. The associations were analyzed between mtDNA deletion patterns, myopathological changes, and clinical characteristics. RESULTS: In total, 155 patients with mitochondrial PEO carrying single large-scale mtDNA mutations were enrolled, including 137 chronic progressive external ophthalmoplegia (CPEO) and 18 Kearns-Sayre syndrome (KSS) patients. The onset ages were 9.61 ± 4.12 in KSS and 20.15 ± 9.06 in CPEO. The mtDNA deletions ranged from 2225 bp to 9131 bp, with m.8470_13446del being the most common. The KSS group showed longer deletions than the CPEO group (p = 0.004). Additionally, a higher number of deleted genes encoding respiratory chain complex subunits (p = 0.001) and tRNA genes (p = 0.009) were also observed in the KSS group. A weak negative correlation between the mtDNA deletion size and ages of onset (p < 0.001, r = -0.369) was observed. The proportion of ragged red fibers, ragged blue fibers, and cytochrome c negative fibers did not correlate significantly with onset ages (p > 0.05). However, a higher percentage of abnormal muscle fibers corresponds to an increased prevalence of exercise intolerance, limb muscle weakness, dysphagia, and cerebellar ataxia. CONCLUSION: We reported a large Chinese cohort consisting of mitochondrial PEO patients with single large-scale mtDNA deletions. Our results demonstrated that the length and locations of mtDNA deletions may influence onset ages and clinical phenotypes. The severity of muscle pathology could not only indicate diagnosis but also may be associated with clinical manifestations beyond the extraocular muscles.

Ocular manifestations of mitochondrial neurogastrointestinal encephalomyopathy: A case report and literature review.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal recessive multisystem disorder that often presents with gastrointestinal and neurological symptoms. Here we report a 33-year-old male who presented with a 16-year history of diarrhea with black stool and progressive weight loss. He complained of progressive bilateral blurred vision, upper eyelids heaviness, ocular motility impairment, and color blindness. Peripheral neuropathy, bilateral sensorineural deafness, hyperlactatemia, diabetes mellitus, hepatic steatosis, blood coagulation dysfunction, and diffuse leukoencephalopathy were detected in the systemic evaluation. Based on the novel homozygous pathogenic variant in the TYMP gene (c.1159+1G>A), he was diagnosed with MNGIE. On ophthalmic examinations, the thickness of the inner retina and ganglion cell complex significantly decreased. ERG showed diffusely decreased amplitudes. The electronegative electroretinogram, which was first reported in MNGIE, indicated a more severe inner retina impairment. The bilateral papillomacular bundle defect and central vision loss in MNGIE are consistent with classical mitochondrial optic neuropathies' features. According to the literature, pigmentary retinopathy, optic neuropathy, and abnormal pupillary reflexes are uncommon ocular features of MNGIE. This study contributes to a better understanding of ocular manifestations in MNGIE and demonstrates that MNGIE may have dyschromatopsia and an electronegative electroretinogram.

Titin related myopathy with ophthalmoplegia. A novel phenotype.

Titin-related myopathy is an emerging genetic neuromuscular disorder with a wide spectrum of clinical phenotypes. To date, there have not been reports of patients with this disease that presented with extraocular muscle involvement. Here we discuss a 19-year-old male with congenital weakness, complete ophthalmoplegia, thoracolumbar scoliosis, and obstructive sleep apnea. Muscle magnetic resonance imaging revealed severe involvement of the gluteal and anterior compartment muscles, and clear adductor sparing, while muscle biopsy of the right vastus lateralis showed distinctive cap-like structures. Trio Whole Exome Sequencing (WES) showed compound heterozygous likely pathologic variants in the TTN gene. (c.82541_82544dup (p.Arg27515Serfs*2) in exon 327 (NM_001267550.2) and c.31846+1G>A (p.?) in exon 123 (NM_001267550.2). To our knowledge, this is the first report of a TTN-related disorder associated with ophthalmoplegia.

Progressive external ophthalmoplegia.

Progressive external ophthalmoplegia (PEO), characterized by ptosis and impaired eye movements, is a clinical syndrome with an expanding number of etiologically distinct subtypes. Advances in molecular genetics have revealed numerous pathogenic causes of PEO, originally heralded in 1988 by the detection of single large-scale deletions of mitochondrial DNA (mtDNA) in skeletal muscle of people with PEO and Kearns-Sayre syndrome. Since then, multiple point variants of mtDNA and nuclear genes have been identified to cause mitochondrial PEO and PEO-plus syndromes, including mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) and sensory ataxic neuropathy dysarthria ophthalmoplegia (SANDO). Intriguingly, many of those nuclear DNA pathogenic variants impair maintenance of the mitochondrial genome causing downstream mtDNA multiple deletions and depletion. In addition, numerous genetic causes of nonmitochondrial PEO have been identified.

Macrocytosis in Mitochondrial DNA Deletion Syndromes.

Large single mitochondrial DNA (mtDNA) deletion syndrome is a rare inborn error of metabolism with variable heteroplasmy levels and clinical phenotype among affected individuals. Chronic progressive external ophthalmoplegia (CPEO) is the most common phenotype in adults with this form of mitochondrial disease [J Intern Med. 2020;287(6):592-608 and Biomed Rep. 2016;4(3):259-62]. The common CPEO clinical manifestations are ptosis and ophthalmoplegia. More variable phenotypic manifestations of CPEO (CPEO plus) include involvement of the peripheral nervous system and myopathy. Here, we describe a 62-year-old female with CPEO and the major mtDNA deletion present at 40% heteroplasmy, who had a coexistent previously undescribed CPEO phenotypic feature of persistent unexplained macrocytosis without anemia. Building on this case, we reviewed other major mtDNA deletion cases seen in our Adult Metabolic Diseases Clinic (AMDC) at the University of British Columbia, Vancouver, Canada, from 2016 to 2022. The major mtDNA deletion cases (n = 26) were compared with mtDNA missense variants identified in the clinic over the same period who acted as the comparison group (n = 16). Of these, the most frequent diagnosis was maternally inherited diabetes and deafness and mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes. Ten out of 26 (38%) of mtDNA deletion patients had macrocytosis with elevated mean corpuscular volume (MCV), median (interquartile range) of 108 fL (102-114 fL). Seven of the patients with macrocytosis had no pertinent etiology. None of the comparison group had macrocytosis. There was a significant difference (p = 0.000) between the MCV and MCH in the mtDNA deletion group compared to the comparison group. This communication sheds light on the association of macrocytosis with the mtDNA deletion syndrome. It would be of great interest to determine if the association is found in other mitochondrial disease clinic populations.

Chronic progressive external ophthalmoplegia plus syndrome due to homozygous missense variant in TOP3A gene.

Chronic progressive external ophthalmoplegia (CPEO) plus syndrome due to pathogenic biallelic variants in TOP3A gene has been described in only one single patient. We report two adult siblings with c.614A>G (p.Asp205Gly) homozygous missense variant in the TOP3A gene who had CPEO plus syndrome.

Phenotype, genotype, and management of congenital fibrosis of extraocular muscles type 1 in 16 Chinese families.

PURPOSE: Congenital 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. METHODS: The 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. RESULTS: Affected 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. CONCLUSION: Instead 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.

[Chronic progressive external ophthalmoplegia that could not be diagnosed by biceps muscle biopsy, but was genetically diagnosed by extraocular muscle biopsy].

A 48-year-old Japanese male experienced slowly progressive diplopia. He had no family history and was negative for the edrophonium chloride test. Blood analysis showed elevated lactic acid and pyruvic acid levels, suggesting mitochondrial disease. A muscle biopsy from the biceps brachii was performed, but no pathological or genetical mitochondrial abnormalities were detected. Subsequently, he underwent muscle plication for diplopia in which the right inferior rectus muscle was biopsied. Genetic examination of genomic DNA extracted from the extraocular muscle tissue revealed multiple mitochondrial gene deletions, with a heteroplasmy rate of approximately 35%, resulting in the diagnosis of chronic progressive external ophthalmoplegia. In mitochondrial diseases, the tissue distribution of mitochondria with disease-associated variants in mtDNA should be noted, and it is important to select the affected muscle when performing a biopsy for an accurate diagnosis.

Distal Arthrogryposis type 5 in an Italian family due to an autosomal dominant gain-of-function mutation of the PIEZO2 gene.

BACKGROUND: Arthrogryposis multiplex congenita (AMC) is a group of clinically and etiologically heterogeneous conditions, characterized by prenatal onset contractures affecting two or more joints. Its incidence is about 1 in 3000 live births. AMC may be distinguished into amyoplasia, distal and syndromic arthrogryposis. Distal arthrogryposis (DA) predominantly affects hands and feet. It is currently divided into more than ten subtypes (DA1, DA2A/B, DA3-10), based on clinical manifestations, gene mutations and inheritance pattern. Among them, only a few patients with DA5 have been reported. It is associated to a gain-of-function pathogenic variant of the PIEZO2 gene, encoding for an ion-channel necessary to convert mechanical stimulus to biological signals and crucial for the development of joints, neuromuscular and respiratory systems. Main clinical features include multiple distal contractures, short stature, ptosis, ophthalmoplegia and, in some cases, restrictive lung disease. CASE PRESENTATION: Hereby, we report on a four-generation Italian family with DA5. Our first proband was a newborn with prenatal suspicion of AMC. At birth, clinical findings were compatible with a DA diagnosis. Family history was positive for the mother with short stature, ophthalmoplegia, short neck, and contractures of the joints of distal extremities, and for three other relatives on the maternal side, including grandfather and great-grandmother, who all shared similar findings. Thus, we performed a next generation sequencing analysis (NGS) of the genes associated to AMC and of those involved in DA. The gain-of-function heterozygous mutation c.8181_8183delAGA (p.Glu2727del) of PIEZO2 was identified in the proband, and the same mutation was also found in the mother, confirming the autosomal dominant inheritance of the condition. CONCLUSIONS: Our patients contribute to the current DA5 genomic database, and to a better characterization of the disease. Clinicians may have suspicion of a DA diagnosis based on suggestive (also prenatal) clinical findings, which must be then confirmed by NGS analysis. Since natural history varies widely among different DA disorders, detection of the underlying causal variant is essential for the identification of the exact subtype, and to its adequate management, which must rely on a multidisciplinary and individualized approach.

Infantile esotropia in a family with TUBB3 mutation associated congenital fibrosis of extraocular muscles.

BACKGROUND: The TUBB3 gene has been reported to be associated with type 3 congenital fibrosis of the extraocular muscles (CFEOM). The clinical features of CFEOM3 that are linked to TUBB3 mutations are diverse, ranging from mild ptosis and limitation of extraocular movement to severe ocular motility problems and central nervous system abnormalities. MATERIALS AND METHODS: This was a single retrospective case report. RESULT: This case report describes a patient with infantile esotropia, who had a heterozygous variant in TUBB3 c.904 G > A (p.A302T) known to cause CFEOM3 and her family members, who presented with manifestations associated with CFEOM3. CONCLUSION: Given the diverse clinical features of CFEOM3, the possibility of the occurrence of CFEOM3 should be considered when there is a congenital abnormality of extraocular muscle movement and a positive family history.

A Novel De Novo TUBB3 Variant Causing Developmental Delay, Epilepsy and Mild Ophthalmological Symptoms in a Chinese Child.

Heterozygous missense mutations in TUBB3 have been implicated in various neurological disorders encompassing either isolated congenital fibrosis of the extraocular muscles type 3 (CFEOM3) or complex cortical dysplasia with other brain malformations 1 (CDCBM1). The description of seizures in patients with TUBB3 mutations is rare. Here, we reported a patient who had febrile seizures before and focal seizure this time, which was diagnosed as epilepsy in combination with an abnormal EEG. MRI showed hypoplastic corpus callosum. Mutation analysis showed a novel de novo heterozygous variant of the TUBB3 gene (NM_006086), c.763G > A (p.V255I). The patient had global developmental delay, photophobia and elliptic pupils, but lacking extraocular muscle involvement and malformations of cortical development, which might be a less severe phenotype of TUBB3 mutations. This is the first report of elliptic pupils in a patient with TUBB3 mutations and expands the spectrum of TUBB3 phenotypes. It indicates that the phenotypic range of TUBB3 mutations might exist on more of a continuum than as a discrete entity, with severity ranging from mild to severe. Further studies are needed to elucidate the complete spectrum of TUBB3-related phenotypes.

Identical twins with progressive kyphoscoliosis and ophthalmoplegia.

The possible differential diagnoses for children presenting with kyphoscoliosis, skeletal deformities and ophthalmoplegia are diverse. We present 11-year-old identical twins with these symptoms, with interesting etiological concern for those practicing in the fields of neurology, pediatrics, spine surgery and related specialties. A new presentation for a rare genetic condition was the final diagnosis for our patients. In this movement disorder round we describe our approach to this clinical constellation and discuss clinical significance of this genetic condition.

TUBB3 Arg262His causes a recognizable syndrome including CFEOM3, facial palsy, joint contractures, and early-onset peripheral neuropathy.

Microtubules are formed from heterodimers of alpha- and beta-tubulin, each of which has multiple isoforms encoded by separate genes. Pathogenic missense variants in multiple different tubulin isoforms cause brain malformations. Missense mutations in TUBB3, which encodes the neuron-specific beta-tubulin isotype, can cause congenital fibrosis of the extraocular muscles type 3 (CFEOM3) and/or malformations of cortical development, with distinct genotype-phenotype correlations. Here, we report fourteen individuals from thirteen unrelated families, each of whom harbors the identical NM_006086.4 (TUBB3):c.785G>A (p.Arg262His) variant resulting in a phenotype we refer to as the TUBB3 R262H syndrome. The affected individuals present at birth with ptosis, ophthalmoplegia, exotropia, facial weakness, facial dysmorphisms, and, in most cases, distal congenital joint contractures, and subsequently develop intellectual disabilities, gait disorders with proximal joint contractures, Kallmann syndrome (hypogonadotropic hypogonadism and anosmia), and a progressive peripheral neuropathy during the first decade of life. Subsets may also have vocal cord paralysis, auditory dysfunction, cyclic vomiting, and/or tachycardia at rest. All fourteen subjects share a recognizable set of brain malformations, including hypoplasia of the corpus callosum and anterior commissure, basal ganglia malformations, absent olfactory bulbs and sulci, and subtle cerebellar malformations. While similar, individuals with the TUBB3 R262H syndrome can be distinguished from individuals with the TUBB3 E410K syndrome by the presence of congenital and acquired joint contractures, an earlier onset peripheral neuropathy, impaired gait, and basal ganglia malformations.

A review of core myopathy: central core disease, multiminicore disease, dusty core disease, and core-rod myopathy.

Core myopathies are clinically, pathologically, and genetically heterogeneous muscle diseases. Their onset and clinical severity are variable. Core myopathies are diagnosed by muscle biopsy showing focally reduced oxidative enzyme activity and can be pathologically divided into central core disease, multiminicore disease, dusty core disease, and core-rod myopathy. Although RYR1-related myopathy is the most common core myopathy, an increasing number of other causative genes have been reported, including SELENON, MYH2, MYH7, TTN, CCDC78, UNC45B, ACTN2, MEGF10, CFL2, KBTBD13, and TRIP4. Furthermore, the genes originally reported to cause nemaline myopathy, namely ACTA1, NEB, and TNNT1, have been recently associated with core-rod myopathy. Genetic analysis allows us to diagnose each core myopathy more accurately. In this review, we aim to provide up-to-date information about core myopathies.

A 7-year old female with arthrogryposis multiplex congenita, Duane retraction syndrome, and Marcus Gunn phenomenon due to a ZC4H2 gene mutation: a clinical presentation of the Wieacker-Wolff syndrome.

Background: Duane retraction syndrome and arthrogryposis multiplex congenita have an incidence of approximately 1:1500-1:3000 live births. However, the association of these two entities with a Marcus-Gunn might be a rare and, until now, under-recognized clinical presentation of the Wieacker-Wolff Syndrome.Patient and methods: We report a 7-year-old female with dysmorphic features, global developmental delay, arthrogryposis multiplex congenita (AMC), Duane retraction syndrome (DRS), and unilateral Marcus Gunn jaw winking.Results: Whole Exome Sequencing showed a de novo premature stop codon in ZC4H2. Extensive genetic and metabolic work was negative otherwise and Brain MRI showed delayed non-specific myelination abnormalities. She continues to have significant delays but does not have regression, seizures or other neurological complications. She has required a multidisciplinary approach for the management of her multiple contractures.Conclusion: This case confirms ZC4H2 as a cause of syndromic DRS and extends the ZC4H2 phenotype to include Marcus Gunn jaw winking.