Oculopharyngeal muscular dystrophy with PABPN1 mutation in a Chinese Malaysian woman

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

Background

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset muscular dystrophy characterised by slowly progressive ptosis, dysphagia, and proximal limb muscle weakness. A common cause of OPMD is the short expansion of a GCG or GCA trinucleotide repeat in PABPN1 gene.

Case presentation

A 78-year-old woman presented with ptosis and gradually progressive dysphagia. Her son had the same symptoms. A physical examination and muscle imaging (MRI and ultrasound) showed impairment of the tongue, proximal muscles of the upper limbs, and flexor muscles of the lower limbs. Needle-electromyography (EMG) of bulbar and facial muscles revealed a myopathic pattern. Based on the characteristic muscle involvement pattern and needle-EMG findings, we suspected that the patient had OPMD. Gene analysis revealed PABPN1 c.35G > C point mutation, which mimicked the effect of a common causative repeat expansion mutation of OPMD.

Conclusion

We herein describe the first reported Japanese case of OPMD with PABPN1 point mutation, suggesting that this mutation is causative in Asians as well as in Europeans, in whom it was originally reported.

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.

Oculopharyngeal Muscular Dystrophy, an Often Misdiagnosed Neuromuscular Disorder: A Southern California Experience

OBJECTIVE

Oculopharyngeal muscular dystrophy (OPMD) is a rare neuromuscular disorder characterized by late-onset development of bilateral eyelid ptosis, ophthalmoparesis and dysphagia with further progression to proximal limb muscle weakness that is an under recognized condition. The mode of inheritance is usually autosomal dominant, but a recessive form has been reported. OPMD is caused by a short expansion of the alanine repeat (GCN trinucleotide) in the poly(adenylate)-binding protein nuclear1 (PABPN1) gene.

METHODS

We performed a retrospective review of undiagnosed cases that initially presented with ptosis, diplopia, dysphagia, muscle weakness, muscular dystrophy and/or myasthenia gravis from 2000 to 2015 at two institutions in Southern California.

RESULTS

Twenty-five patients were identified to have OPMD with genetic confirmation.

CONCLUSIONS

Even though a rare condition, the prevalence is disproportionally frequent in certain ethnic groups and in certain regions; thus, we report our experience of OPMD patients in Southern California.

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.

Oculopharyngeal muscular dystrophy --an under-diagnosed disease in China? Report a China-born Chinese with PABPN1 mutation and epidemiology review of the literature

BACKGROUND/PURPOSE

Most reports about oculopharyngeal muscular dystrophy (OPMD) have been contributed by occidental countries, and most of the victims of this disease are racially white. In contrast, this disorder is rarely seen in Asians and has only one African report. Consequently, OPMD has been regarded as a disease of the Western world. The purpose of this paper is to challenge the accuracy of this concept.

METHODS

In a Chinese immigrant family, 3 patients manifesting signs related to OPMD were examined. Electromyography, nerve conduction studies, muscle biopsy and genetic analysis were performed on the proband. All the 322 papers about OPMD were reviewed and their country of origin was labeled to perceive the approximate prevalence of OPMD. Countries were categorized into groups according to the continents to which they belonged.

RESULTS

The proband's muscle histopathology showed small angulated fiber with rimmed vacuoles, ultrastructural pathology exposed filamentous intranuclear inclusions, and genetic analysis of the polyadenylate binding protein nuclear 1(PABPN1) gene revealed 13 GCG trinucleotide repeats in one allele (GCG)13 while being normal in the other. The survey of the country of origin of OPMD reports showed that 80% of these papers were contributed by occidental countries and that the number of publications of OPMD among countries of Americas and Asia were unequal, when compared to those of European countries, which were fairly proportioned. An epidemiologic review of the literature is presented and the prevalence of OPMD is discussed.

CONCLUSION

This is a China-born Chinese patient with both morphologically and genetically proven of OPMD. The very low OPMD report rate in developing countries of East Asia is due to the unfamiliarity of medical workers to OPMD and the unavailability of medical supplies to confirm the diagnosis. In addition, the present and previous reports provide clear evidence that OPMD in these areas is underdiagnosed.

Mutation and haplotype analysis of oculopharyngeal muscular dystrophy in Thai patients

Oculopharyngeal muscular dystrophy (OPMD) is an inherited neuromuscular disease associated with a short trinucleotide repeat expansion in Exon 1 of the PABPN1 gene. OPMD is uncommon in East Asian populations, and there have been no previous reports of Thai patients. We studied clinical and molecular genetic features of six unrelated Thai patients with autosomal dominant OPMD. All patients had expansions of the guanine-cytosine-guanine (GCG) repeat ranging from three to seven additional repeats in the PABPN1 gene. Haplotype analysis showed that these mutations might have originated independently. Analysis of the size of the GCG repeat in the PABPN1 gene in 200 Thai control patients showed that 0.5% of the control subjects possessed (GCG)(7), thereby suggesting that the prevalence of autosomal recessive OPMD in the Thai population was approximately 1 in 160,000. In conclusion, our data suggest that OPMD in Thailand may be more common than previously thought.

Gene diagnosis of oculopharyngeal muscular dystrophy in a Chinese family by a GeneScan method

This study aims to perform gene diagnosis for Chinese family patients with Oculopharyngeal muscular dystrophy (OPMD). Genomic DNAs were extracted from the pedigrees' members. Gene diagnosis was performed for these pedigrees' members by approaches, such as DNA sequencing and GeneScan. Sequence analysis and PABPN1 genotyping showed that the mutated allele in affected members of this family has nine trinucleotide repeats of GCG (GCG)(9), whereas the normal allele contains six trinucleotide repeats of GCG (GCG)(6). The above results suggest that mutated GCG repeats in PABPN1 gene may cause OPMD in this family, and PABPN1 genotyping could be used as a convenient, highly effective, and reliable gene diagnostic test for OPMD patients.

Study of a Taiwanese family with oculopharyngeal muscular dystrophy

BACKGROUND

Oculopharyngeal muscular dystrophy (OPMD) is a late onset autosomal dominant muscle disorder. OPMD is caused by a short trinucleotide repeat expansion encoding an expanded polyalanine tract in the polyadenylate binding-protein nuclear 1 (PABPN1) gene. We identified and characterized a PABPN1 mutation in a Taiwanese family with OPMD.

METHODS

The phenotypic and genotypic characteristics of all subjects were evaluated in a Taiwanese OPMD family. Genetic alterations in the PABPN1 gene were identified using PCR and DNA sequencing.

RESULTS

Ten subjects with OPMD (6 symptomatic and 4 asymptomatic) within the Taiwanese family carried a novel mutation in the PABPN1 gene. The normal (GCG)6(GCA)3GCG sequence was replaced by (GCG)6(GCA)(GCG)4(GCA)3GCG due to an insertion of (GCG)4GCA into the normal allele in the Taiwanese OPMD subjects.

CONCLUSIONS

In contrast to a single GCG expansion in most of OPMD patients in the literature, an insertion of (GCG)4GCA in the PABPN1 gene was found in the Taiwanese OPMD subjects. The identification of this mutation appears to support the molecular mechanism of unequal cross-over of two PABPN1 alleles.