Genotype and phenotype study of 34 Spanish patients diagnosed with oculopharyngeal muscular dystrophy

Ocular manifestations and outcomes of OPMD- a report from the national IsrOPMD registry

PURPOSE

This study aims to describe the ocular manifestations, treatment, and prognosis of OPMD patients registered in the national Israel OPMD(IsrOPMD) registry.

METHODS

Data was prospectively collected from patients referred to the IsrOPMD registry from January 2022 to March 2023. This included patient demographics, medical and ocular history, eye exams, eyelid evaluations, visual field exams, and orthoptic evaluations.

RESULTS

30 patients (15 males, mean age 53 years) were treated in the ocular OPMD clinic, predominantly of Bukhari descent (86.6%). The mean visual acuity was 0.06 logMAR. Twenty-one patients (70%) had eye movement problem, mostly in horizontal gaze. 6(20%) patients' complaint about diplopia. Ptosis surgery was performed in 21(70%) patients, with 17(56.7%) patients underwent frontalis sling surgery and 4(13.3%) patients undergoing levator advancement. The mean Margin reflex distance (MRD1) improved post-surgery (2.28 mm vs. 1.58 mm), but 11(36.6%) patients required more than one ptosis surgery.

CONCLUSIONS

The study contributes valuable insights into the ocular aspects of OPMD. It reveals that OPMD patients often experience a range of ocular symptoms, such as ptosis, abnormalities in eye movements, strabismus, and potentially diplopia, which can significantly impact their quality of life. The findings underscore the importance of regular ophthalmological follow-up for these patients to address these symptoms effectively. The study is significant in contributing to the limited but growing knowledge about the ocular manifestations of OPMD and the management of these symptoms to improve the quality of life for patients suffering from this condition.

Emerging and established biomarkers of oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is a rare, primarily autosomal dominant, late onset muscular dystrophy commonly presenting with ptosis, dysphagia, and subsequent weakness of proximal muscles. Although OPMD diagnosis can be confirmed with high confidence by genetic testing, the slow progression of OPMD poses a significant challenge to clinical monitoring and a barrier to assessing the efficacy of treatments during clinical trials. Accordingly, there is a pressing need for more sensitive measures of OPMD progression, particularly those which do not require a muscle biopsy. This review provides an overview of progress in OPMD biomarkers from clinical assessment, quantitative imaging, histological assessments, and genomics, as well as hypothesis-generating "omics" approaches. The ongoing search for biomarkers relevant to OPMD progression needs an integrative, longitudinal approach combining validated and experimental approaches which may include clinical, imaging, demographic, and biochemical assessment methods. A multi-omics approach to biochemical biomarker discovery could help provide context for differences found between individuals with varying levels of disease activity and provide insight into pathomechanisms and prognosis of OPMD.

Characterization of muscle strength and mobility in oculopharyngeal muscular dystrophy

INTRODUCTION/AIMS

Muscle weakness, and its association with mobility limitations, has received little study in oculopharyngeal muscular dystrophy (OPMD) using quantitative and standardized assessments. The objectives of this study were to (1) document upper and lower limb muscle strength, upper limb functions, fatigue, and mobility capacities; (2) compare them with reference values and across participant age groups; and (3) explore associations between muscle strength, fatigue, and mobility capacities among adults with OPMD.

METHODS

Thirty-four participants were included in this cross-sectional study. The following variables were assessed: quantitative maximal isometric muscle strength, grip and pinch strength, fatigue, walking speed, walking endurance, sit-to-stand, and stair ascent and descent capacities.

RESULTS

Muscle strength was lower for older than younger participants for five muscle groups (P < .05). Walking endurance, sit-to-stand, stairs (ascent and descent), and strength of hip flexion, grip, and pinch were below 80% of reference values in participants ≥56 y old (55.3%-78.2%). Moderate to strong correlations were found between muscle strength and mobility capacities (ρ = 0.42-0.80, P < .05), and between fatigue and either muscle strength or mobility capacities (ρ = 0.42-0.75, P < .05).

DISCUSSION

This study highlights the impact of OPMD on strength, endurance, and functional capacity, among others, with patients being well below reference values even before the age of 65 y. In addition to helping health professionals to offer better clinical guidance, these results will improve clinical trial readiness. The next steps will be to assess the metrological properties of outcome measures and continue to document the disease progression rate.

The phenotypic and genotypic features of Chinese patients with oculopharyngeal muscular dystrophy

OBJECTIVE

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset inherited neuromuscular disorder, with progressive ptosis and dysphagia as common manifestations. To date, OPMD has rarely been reported among East Asians. The present study summarizes the phenotypic and genotypic features of Chinese patients with OPMD.

METHODS

Twenty-one patients with molecularly confirmed OPMD from 9 unrelated families were identified by direct sequencing of the polyadenlyate binding protein nuclear-1 (PABPN1) gene. Immunofluorescence staining of muscle biopsies was conducted to identify the components of protein degradation pathways involved in OPMD.

RESULTS

In our cohort, the genetically confirmed OPMD group had a mean age at onset of 50.6 ± 4.2 years (range 45-60 years). Ptosis (42.9%) was the most common initial symptom; patients with ptosis as the first symptom subsequently developed dysphagia within a median time of 5.5 years (range 1-19 years). Evidence of external ophthalmoplegia was found in 38.1% of patients. A total of 33.3% of the patients developed muscle weakness at a median age at onset of 66 years (range 50-70 years), with neck flexor involvement in all patients. Five genotypes were observed in our cohort, including classical (GCG)9-11 repeats in 7 families and non-GCG elongations with additional GCA expansions in 2 families. OPMD muscle biopsies revealed rimmed vacuoles and intranuclear filamentous inclusions. The PABPN1 protein showed substantial accumulation in the nuclei of muscle fiber aggregates and closely colocalized with p62, LC3B and FK2.

INTERPRETATION

Our findings indicate wide genetic heterogeneity in OPMD in the Chinese population and demonstrate abnormalities in protein degradation pathways in this disease.

Assessment of PABPN1 nuclear inclusions on a large cohort of patients and in a human xenograft model of oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is a rare muscle disease characterized by an onset of weakness in the pharyngeal and eyelid muscles. The disease is caused by the extension of a polyalanine tract in the Poly(A) Binding Protein Nuclear 1 (PABPN1) protein leading to the formation of intranuclear inclusions or aggregates in the muscle of OPMD patients. Despite numerous studies stressing the deleterious role of nuclear inclusions in cellular and animal OPMD models, their exact contribution to human disease is still unclear. In this study, we used a large and unique collection of human muscle biopsy samples to perform an in-depth analysis of PABPN1 aggregates in relation to age, genotype and muscle status with the final aim to improve our understanding of OPMD physiopathology. Here we demonstrate that age and genotype influence PABPN1 aggregates: the percentage of myonuclei containing PABPN1 aggregates increases with age and the chaperone HSP70 co-localize more frequently with PABPN1 aggregates with a larger polyalanine tract. In addition to the previously described PRMT1 and HSP70 co-factors, we identified new components of PABPN1 aggregates including GRP78/BiP, RPL24 and p62. We also observed that myonuclei containing aggregates are larger than myonuclei without. When comparing two muscles from the same patient, a similar amount of aggregates is observed in different muscles, except for the pharyngeal muscle where fewer aggregates are observed. This could be due to the peculiar nature of this muscle which has a low level of PAPBN1 and contains regenerating fibers. To confirm the fate of PABPN1 aggregates in a regenerating muscle, we generated a xenograft model by transplanting human OPMD muscle biopsy samples into the hindlimb of an immunodeficient mouse. Xenografts from subjects with OPMD displayed regeneration of human myofibers and PABPN1 aggregates were rapidly present-although to a lower extent-after muscle fiber regeneration. Our data obtained on human OPMD samples add support to the dual non-exclusive models in OPMD combining toxic PABPN1 intranuclear inclusions together with PABPN1 loss of function which altogether result in this late-onset and muscle selective disease.

Recent Progress in Oculopharyngeal Muscular Dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset intractable myopathy, characterized by slowly progressive ptosis, dysphagia, and proximal limb weakness. It is caused by the abnormal expansion of the alanine-encoding (GCN)n trinucleotide repeat in the exon 1 of the polyadenosine (poly[A]) binding protein nuclear 1 gene (11-18 repeats in OPMD instead of the normal 10 repeats). As the disease progresses, the patients gradually develop a feeling of suffocation, regurgitation of food, and aspiration pneumonia, although the initial symptoms and the progression patterns vary among the patients. Autologous myoblast transplantation may provide therapeutic benefits by reducing swallowing problems in these patients. Therefore, it is important to assemble information on such patients for the introduction of effective treatments in nonendemic areas. Herein, we present a concise review of recent progress in clinical and pathological studies of OPMD and introduce an idea for setting up a nation-wide OPMD disease registry in Japan. Since it is important to understand patients' unmet medical needs, realize therapeutically targetable symptoms, and identify indices of therapeutic efficacy, our attempt to establish a unique patient registry of OPMD will be a helpful tool to address these urgent issues.

A study of impairments in oculopharyngeal muscular dystrophy

INTRODUCTION

In this study we aimed to document the prevalence and age of onset of motor impairments and other key symptoms in oculopharyngeal muscular dystrophy (OPMD).

METHODS

Retrospective chart review of patients followed at the Saguenay Neuromuscular Clinic (Quebec, Canada).

RESULTS

A total of 333 participants with the (GCN)₁₃ mutation were included. Before the age of 75 years, 27% of them had walking limitations, 14% could not climb stairs independently, and 14% used a wheelchair for long distances or daily living. The median age of onset was 54 years for ptosis and dysphagia and 58 years for lower limb proximal weakness. Other frequent symptoms included fatigue, pharyngeal pooling of thickened secretions, and dysphonia. The median age at death was 77 years and the main cause was respiratory disease.

DISCUSSION

This study provides important information to help anticipatory guidance for affected people and for the development of therapeutic trials in OPMD.

Diagnostics of short tandem repeat expansion variants using massively parallel sequencing and componential tools

Short tandem repeats (STRs) are scattered throughout the human genome. Some STRs, like trinucleotide repeat expansion (TRE) variants, cause hereditable disorders. Unambiguous molecular diagnostics of TRE disorders is hampered by current technical limitations imposed by traditional PCR and DNA sequencing methods. Here we report a novel pipeline for TRE variant diagnosis employing the massively parallel sequencing (MPS) combined with an opensource software package (FDSTools), which together are designed to distinguish true STR sequences from STR sequencing artifacts. We show that this approach can improve TRE diagnosis, such as Oculopharyngeal muscular dystrophy (OPMD). OPMD is caused by a trinucleotide expansion in the PABPN1 gene. A short GCN expansion, (GCN[10]), coding for a 10 alanine repeat is not pathogenic, but an alanine expansion is pathogenic. Applying this novel procedure in  a Dutch OPMD patient cohort, we found expansion variants from GCN[11] to GCN[16], with the GCN[16] as the most abundant variant. The repeat expansion length did not correlate with clinical features. However, symptom severity was found to correlate with age and with the initial affected muscles, suggesting that aging and muscle-specific factors can play a role in modulating OPMD.

Correlation between PABPN1 genotype and disease severity in oculopharyngeal muscular dystrophy

OBJECTIVE

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant adult-onset disease characterized by progressive ptosis, dysphagia, and proximal limb weakness. The genetic cause is an expanded (GCN)n mutation in the PABPN1 gene encoding for the polyadenylate-binding protein nuclear 1. We hypothesized a potential correlation between the size of the (GCN)n expansion and the severity of the phenotype. To do this, we characterized the distribution of the genotypes as well as their correlation with age at diagnosis and phenotypical features in a large cohort of heterozygous and homozygous patients with OPMD in France with a confirmed molecular diagnosis of PABPN1.

METHODS

We explored 354 unrelated index cases recruited between 1999 and 2014 in several neuromuscular centers in France.

RESULTS

This cohort allowed us to characterize the frequency of mutated alleles in the French population and to demonstrate a statistical correlation between the size of the expansion and the mean age at diagnosis. We also confirmed that homozygous patients present with a more severe disease.

CONCLUSIONS

It has been difficult to establish phenotype-genotype correlations because of the rare nature of this disease. Our work demonstrates that patients with OPMD with longer PABPN1 expansion are on average diagnosed at an earlier age than patients with a shorter expansion, confirming that polyalanine expansion size plays a role in OPMD, with an effect on disease severity and progression.

Characterization of PABPN1 expansion mutations in a large cohort of Mexican patients with oculopharyngeal muscular dystrophy (OPMD)

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal-dominant, adult-onset disorder defined by blepharoptosis, dysphagia, and proximal muscle weakness. OPMD arises from heterozygous expansions of a trinucleotide (GCN) tract situated at the 5' region of the polyadenylate RNA binding protein 1 (PABPN1) gene. The frequency of a particular (GCN) expansion in a given population of patients with OPMD is largely influenced by the occurrence of founder mutations. Analysis of large groups of patients with OPMD from different ethnic origins will help to estimate the relative contribution of each expanded allele to the disease. The purpose of this study was to characterize the type of PABPN1 expanded alleles in a large cohort of OPMD individuals from Mexico. Molecular analysis procedures included genomic DNA extraction from blood leukocytes in each patient followed by PCR amplification of PABPN1 exon 1, and direct nucleotide sequencing of PCR products. A total of 102 patients with OPMD were included in the study. Expanded PABPN1 gene alleles were demonstrated in all patients: 65% (66 out of 102) had a (GCN)15 expansion while the remaining 35% (36 out of 102) exhibited a (GCN)13 expansion. This is one of the largest series of molecularly confirmed patients with OPMD in a non-Caucasian population. Ethnic-specific differences in the prevalence of specific PABPN1 expansions must be considered for genetic screening of patients with OPMD.

PABPN1 (GCN)11 as a Dominant Allele in Oculopharyngeal Muscular Dystrophy -Consequences in Clinical Diagnosis and Genetic Counselling

Oculopharyngeal muscular dystrophy (OPMD) is mainly characterized by ptosis and dysphagia. The genetic cause is a short expansion of a (GCN)10 repeat encoding for polyalanine in the poly(A) binding protein nuclear 1 (PABPN1) gene to (GCN)12–17 repeats. The (GCN)11/Ala11 allele has so far been described to be either a polymorphism or a recessive allele with no effect on the phenotype in the heterozygous state. Here we report the clinical and histopathological phenotype of a patient carrying a single (GCN)11/Ala11 heterozygous allele and presenting an atypical form of OPMD with dysphagia and late and mild oculomotor symptoms. Intranuclear inclusions were observed in his muscle biopsy. This suggests a dominant mode of expression of the (GCN)11/Ala11 allele associated with a partial penetrance of OPMD.

Orthoptic and video-oculographic analyses in oculopharyngeal muscular dystrophy

INTRODUCTION

Mild ophthalmoparesis can be seen in oculopharyngeal muscular dystrophy (OPMD).

METHODS

Orthoptic analysis included assessment of phoria/tropia, eye excursion, saccades, pursuit, stereoacuity, and Hess-Lancaster screen test. Video-oculography included fixation, horizontal and vertical saccades, and pursuit.

RESULTS

Orthoptic abnormalities were: tropia (4 of 6); abnormal eye excursion (4 of 6, 78% involved lateral or superior rectus muscles); abnormal horizontal or vertical saccades (2 of 6); abnormal pursuit (0 of 6); abnormal stereoacuity (2 of 6); and pathological Hess-Lancaster screen (4 of 6). Video-oculographic abnormalities were present for: fixation (1 of 6); saccade latency (1 of 6); horizontal pursuit (3 of 6); and vertical pursuit (0 of 6). For horizontal saccades, mean velocity, peak velocity, and gain were pathological in 5 of 6, 5 of 6 (61% of pathological mean and peak velocities involved abducting eye movements), and 3 of 6, respectively. For vertical saccades, mean velocity, peak velocity, and gain were pathological in 4 of 6, 4 of 6 (53% involved upward movements), and 3 of 6, respectively.

CONCLUSION

The data indicate preferential involvement of lateral and (to a lesser degree) superior rectus muscles in OPMD.

Hip flexion weakness is associated with impaired mobility in oculopharyngeal muscular dystrophy: a retrospective study with implications for trial design

Oculopharyngeal muscular dystrophy (OPMD) is a rare myopathy for which validated outcome measures are lacking, posing a barrier to clinical trials. Our goal was to identify factors associated with impaired mobility in OPMD in order to guide development of surrogate endpoints in future clinical trials. One hundred forty-four individuals with OPMD were included in this retrospective, single-center study. We made novel use of parametric time-to-event analysis to model age at initial use of assistive device for ambulation. We hypothesized that limb weakness and other markers of disease severity are associated with earlier use of assistive devices. 23.6% of individuals (34/144) progressed to use of assistive devices (mean age 66.0 ± 9.6 y). Earlier age at assistive device was associated with hip flexion Medical Research Council grade ≤3 (p <0.0001), earlier disease onset (p <0.0001), and lack of blepharoptosis surgery (p = 0.011). Markers of dysphagia severity were not associated with earlier progression to assistive devices. Our study is the first to show a statistical association between hip flexion weakness and impaired mobility in OPMD, indicating that hip flexion strength could be explored as a surrogate endpoint for use in clinical trials. Since severity of disease features may be discordant within individuals, composite outcome measures are warranted.

Oculopharyngeal muscular dystrophy: phenotypic and genotypic studies in a Chinese population

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant late-onset neuromuscular degenerative disease characterized by ptosis, dysphagia, and proximal muscle weakness. The genetic basis has been identified as an abnormal (GCN) expansion encoding the polyalanine tract in exon 1 of the polyadenylate-binding protein nuclear 1 gene (PABPN1). OPMD is worldwide distributed, but has rarely been reported in East Asians. In this study, we summarized the clinical and genetic characteristics of 34 individuals from 13 unrelated families in Chinese population. In our cohort, the mean age at onset was 47.2 years. Dysphagia, rather than ptosis, was the most common initial symptom. Genetically, we identified seven genotypes in our patients, including one compound heterozygote of (GCN)11/(GCN)12. The genetic heterogeneity implies that there is no single founder effect in Chinese population, and our data also support that the (GCN)11 polymorphism may have a disease-modifying effect. Additionally, the clinical features showed homogeneity within families, which suggests that other genetic factors apart from the already known genotype also play a role in modifying the phenotype.

Screening for the presence of FMR1 premutation alleles in a Spanish population with fibromyalgia

Fragile X mental retardation 1 (FMR1) premutation carriers, who are at risk of having children with fragile X Syndrome, were initially considered as clinically unaffected. However, recent clinical and molecular studies have shifted this point of view. The incidence of premutation in the general population is substantial. Apart from the well-documented fragile X-associated tremor-ataxia and fragile X premature ovarian insufficiency, there is a broad constellation of symptoms including depression, anxiety, muscle pain, autoimmune and thyroid disease, chronic fatigue, and fibromyalgia that has been described, particularly in females with the premutation (55-200 repeats). Fibromyalgia (FM) is the most common cause of widespread pain and comprises a heterogeneous group of patients, affecting 2-3 % of the general population. We analyzed the FMR1 gene in a cohort of females diagnosed with fibromyalgia in order to assess the incidence of premutated alleles. CGG repeat size was determined in 353 females suffering from FM and results were compared with a control group. Four premutated carriers in the FM group were detected. The observed incidence is higher than that described for a normal female population (1/88 vs 1/250). The early detection of premutation carriers for the FMR1 gene among individuals diagnosed with fibromyalgia is important and would be helpful in correct genetic counseling of patients and their families, who may be at risk of having children with fragile X syndrome, the most common known cause of inherited intellectual disability and autism. Our data should be cautiously interpreted based on just this study; nevertheless, screening for the FMR1 gene in FM patients at least with presentations suggestive of FMR1 gene-related disease seems recommendable.