A Japanese case of oculopharyngeal muscular dystrophy (OPMD) with PABPN1 c.35G > C; p.Gly12Ala point mutation

HNRNPA2B1 myopathy presenting in a family with an early onset oculopharyngeal muscular dystrophy-like phenotype

Genetic variation at HNRNPA2B1 is associated with inclusion body myopathy, Paget's disease and paediatric onset oculopharyngeal muscular dystrophy. We present a pedigree where a mother and two daughters presented with adolescent to early-adulthood onset of symptoms reminiscent of oculopharyngeal muscular dystrophy or chronic progressive external ophthalmoplegia, with a later limb-girdle pattern of weakness. Creatine Kinase was ∼1000 U/L. Myoimaging identified fatty replacement of sartorius, adductors longus and magnus, biceps femoris, semitendinosus and gastrocnemii. Muscle biopsies showed a variation of fibre size, occasional rimmed vacuoles and increased internalised myonuclei. Cases were heterozygous for a frameshift variant at HNRNPA2B1, consistent with a dominant and fully-penetrant mode of inheritance. Genetic variation at HNRNPA2B1 should be considered in adults with an oculopharyngeal muscular dystrophy-like or chronic progressive external ophthalmoplegia-like myopathy where initial testing fails to identify a cause.

Characteristics of the muscle involvement along the disease progression in a large cohort of oculopharyngodistal myopathy compared to oculopharyngeal muscular dystrophy

BACKGROUND AND OBJECTIVES

Oculopharyngodistal myopathy (OPDM) is an autosomal dominant myopathy clinically characterized by distal muscle weakness. Even though the identification of four causative genes, LRP12, GIPC1, NOTCH2NLC and RILPL1, it is unclear whether the myopathy progressed similarly among OPDM subtypes. We aimed to establish diagnostic clues in muscle imaging of OPDM in comparison with clinicopathologically similar oculopharyngeal muscular dystrophy (OPMD).

METHODS

Axial muscle CT and/or T1-weighted MRI data from 54 genetically confirmed patients with OPDM (OPDM_LRP12; n = 43, OPDM_GIPC1; n = 6, OPDM_NOTCH2NLC; n = 5) and 57 with OPMD were evaluated. We scored the degree of fat infiltration in each muscle by modified Mercuri score and performed hierarchical clustering analyses to classify the patients and infer the pattern of involvement on progression.

RESULTS

All OPDM subtypes showed a similar pattern of distribution in the affected muscles; soleus and medial gastrocnemius involved in the early stage, followed by tibialis anterior and extensor digitorum longus. For differentiating OPDM and OPMD, severely affected gluteus medius/minimus and adductor magnus was indicative of OPMD.

DISCUSSION

We identified a diagnostic muscle involvement pattern in OPDM reflecting its natural history. The results of this study will help in the appropriate intervention based on the diagnosis of OPDM, including its stage.

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.

Choked: A Case Report of Oculopharyngeal Muscular Dystrophy Mimicking Hypothyroidism From the Philippines

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset myopathic genetic disorder characterized by chronic progressive dysphagia and ptosis with or without proximal limb weakness. It is most often caused by an abnormal alanine-encoding (GCN) trinucleotide repeat expansion in the first exon of the poly(A)-binding protein nuclear 1 (PABPN1) gene. Patients with hypothyroidism may similarly report bilateral ptosis, dysphagia, and limb weakness. Here, we report the case of a 65-year-old Austrian female with hypothyroidism living in the Philippines who presented with gradually progressive ptosis, dysphagia, and intermittent choking episodes. No known relatives had similar symptoms. Physical examination showed bilateral symmetric ptosis, good cough reflex, and good limb muscle strength. Electromyographic studies of facial and laryngeal muscles were found to be normal. Thyroid evaluation showed biochemically hyperthyroid status while taking Levothyroxine. With a clinical suspicion for genetic progressive myopathy, we considered OPMD. Genetic testing revealed abnormal expansion of GCN trinucleotide repeats in the PABPN1 gene. We describe the first reported case of OPMD with detected PABPN1 gene expansion in the Philippines simulating hypothyroidism symptoms, suggesting possible points for misidentification and underdiagnosis of OPMD in developing countries.

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.

A Case of Oculopharyngeal Muscular Dystrophy Caused by a Novel PABPN1 c.34G > T (p.Gly12Trp) Point Mutation without Polyalanine Expansion

Immediately after the initial methionine codon, the PABPN1 gene encodes a stretch of 10 alanines, 1 glycine, and 2 alanines. Oculopharyngeal muscular dystrophy (OPMD) is caused by the expansion of the first 10 alanine stretches. The only exception is the missense mutation of glycine at the 12th residue into alanine, which elongates the stretch to 13 alanines by connecting the first and second stretch with the addition of one alanine in between, indicating that the expansion or elongation of the alanine stretch results in OPMD. We report a 77-year-old man with the novel missense mutation c.34G >  T (p.Gly12Trp) in PABPN1 gene whose clinicopathological findings were compatible with OPMD. He presented with slowly progressive bilateral ptosis, dysphagia, and symmetrical proximal dominant muscle weakness. Magnetic resonance imaging revealed selective fat replacement of the tongue, bilateral adductor magnus, and soleus muscles. Immunohistochemistry studies of the muscle biopsy sample revealed PABPN1-posibive aggregates in the myonuclei which have been reported to be specific to OPMD. This is the first OPMD case caused by neither the expansion nor the elongation of alanine stretch. The present case suggests that OPMD may be caused not only by triplet repeats but also by point mutations.

Muscle ultrasound in hereditary muscle disease

In this review we summarise the key techniques of muscle ultrasound as they apply to hereditary muscle disease. We review the diagnostic utility of muscle ultrasound including its role in guiding electromyography and muscle biopsy sampling. We summarize the different patterns of sonographic muscle involvement in the major categories of genetic muscle disorders and discuss the limitations of the technique. We hope to encourage others to adopt ultrasound in their care for patients with hereditary muscle diseases.