Oculopharyngeal muscular dystrophy, other ocular myopathies, and progressive external ophthalmoplegia

Diagnosis and Management of Seronegative Myasthenia Gravis: Lights and Shadows

Myasthenia gravis (MG) is an antibody-mediated neuromuscular disease affecting the neuromuscular junction. In most cases, autoantibodies can be detected in the sera of MG patients, thus aiding in diagnosis and allowing for early screening. However, there is a small proportion of patients who have no detectable auto-antibodies, a condition termed "seronegative MG" (SnMG). Several factors contribute to this, including laboratory test inaccuracies, decreased antibody production, immunosuppressive therapy, immunodeficiencies, antigen depletion, and immune-senescence. The diagnosis of SnMG is more challenging and is based on clinical features and neurophysiological tests. The early identification of these patients is needed in order to ensure early treatment and prevent complications. This narrative review aims to examine the latest updates on SnMG, defining the clinical characteristics of affected patients, diagnostic methods, management, and therapeutic scenarios.

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.

A complex genomic locus drives mtDNA replicase POLG expression to its disease-related nervous system regions

DNA polymerase gamma (POLG), the mtDNA replicase, is a common cause of mitochondrial neurodegeneration. Why POLG defects especially cause central nervous system (CNS) diseases is unknown. We discovered a complex genomic regulatory locus for POLG, containing three functional CNS‐specific enhancers that drive expression specifically in oculomotor complex and sensory interneurons of the spinal cord, completely overlapping with the regions showing neuronal death in POLG patients. The regulatory locus also expresses two functional RNAs, LINC00925‐RNA and MIR9‐3, which are coexpressed with POLG. The MIR9‐3 targets include NR2E1, a transcription factor maintaining neural stem cells in undifferentiated state, and MTHFD2, the regulatory enzyme of mitochondrial folate cycle, linking POLG expression to stem cell differentiation and folate metabolism. Our evidence suggests that distant genomic non‐coding regions contribute to regulation of genes encoding mitochondrial proteins. Such genomic arrangement of POLG locus, driving expression to CNS regions affected in POLG patients, presents a potential mechanism for CNS‐specific manifestations in POLG disease.

Oculopharyngodistal myopathy--a possible association with cardiomyopathy

Oculopharyngodistal myopathy is an uncommon myopathy characterised clinically by cranial and distal limb muscle weakness. Here we describe two siblings with autosomal dominant oculopharyngodistal myopathy apparently associated with dilated cardiomyopathy, which in one case progressed to ventricular hypertrabeculation/non-compaction. Electrocardiographic screening was normal and the cardiomyopathy was detected only with echocardiography. Our findings suggest that patients with oculopharyngodistal myopathy should be screened for cardiomyopathy (with both electrocardiography and echocardiography).

Mitochondrial diseases: a nosological update

Mitochondrial diseases are disorders caused by impairment of the mitochondrial respiratory chain, characterized by clinical-genetic heterogeneity and frequent multisystemic involvement. It is difficult to establish a precise genotype/phenotype correlation and obtain a definitive nosology. Today's genetic classification distinguishes disorders caused by defects in the mitochondrial genome (sporadic or maternally-inherited) from disorders caused by defects in the nuclear genome (autosomally-inherited). We report an updated classification, briefly review the main clinical syndromes and describe the most recent genetic knowledge.

Reconstructive rhytidectomy?

Muscular dystrophies are commonly considered hereditary progressive degenerative diseases that affect skeletal and cardiac muscles. Oculopharyngeal muscular dystrophy is a rare hereditary disorder of later onset consisting of progressive dysphagia and bilateral blepharoptosis unlike the peripheral muscular weakness common to other muscular dystrophies. The symptoms of progressive dysphagia, with bilateral ptosis, usually occur after the age of 40 years. The authors present a patient with oculopharyngeal muscular dystrophy and chronic facial pain relieved by midface soft tissue support, namely, the reconstructive rhytidectomy.

Management of myogenic ptosis

OBJECTIVE

To review the genetics, clinical features, and management of patients affected by myogenic ptosis.

DESIGN

Retrospective, noncomparative interventional case series.

PARTICIPANTS

Twenty-eight patients with myogenic ptosis.

METHODS

A review of all patients with myogenic ptosis between 1992 and 2000 was made in a tertiary oculoplastics practice.

MAIN OUTCOME MEASURES

Ocular and systemic findings associated with myogenic ptosis were examined. Patients were diagnosed clinically, and ancillary tests (including genetic tests and muscle biopsy histologic findings) were reviewed. Surgical management principles and complications are discussed.

RESULTS

Most of our ptosis patients had chronic progressive external ophthalmoplegia (43%), oculopharyngeal muscular dystrophy (OPMD; 18%), and myotonic dystrophy (18%). Fifty percent of myogenic ptosis patients in our series underwent frontalis suspensions. Twenty-one percent of patients who initially had operations at our institution had minor complications, most related to corneal exposure. The most common ocular finding other than ptosis and ophthalmoplegia was pigmentary retinopathy (25%). The most common systemic finding in our patients was dysphagia (43%). Genetic testing for OPMD was highly sensitive. Muscle biopsy results for mitochondrial myopathies were less accurate as adjunctive diagnostic tests.

CONCLUSIONS

Myogenic ptosis should be considered in the differential diagnosis of any atypical ptosis presentation. To avoid complications, surgery should be performed only when the visual axis is obscured. We recommend the use of silicone slings in any patient with severe ptosis and less than 8 mm of levator function. Genetic testing of patients with myogenic ptosis is important to allow accurate diagnosis and to permit appropriate counseling on potentially life-threatening health issues.