Journal of the Formosan Medical Association (2012) 111, 397e402
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ORIGINAL ARTICLE
Oculopharyngeal muscular dystrophy e An underdiagnosed disease in China? Report a China-born Chinese with PABPN1 mutation and epidemiology review of the literature Yu-Yi Chien* Department of Neurology Keelung Chang Gung Memorial Hospital, Keelung, Taiwan Received 10 December 2010; received in revised form 29 April 2011; accepted 3 June 2011
KEYWORDS epidemiology; filamentous inclusions; oculopharyngeal muscular dystrophy; polyadenylate binding protein nuclear 1 gene; prevalence; rimmed-vacuole
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
* Department of Neurology, Keelung Chang Gung Memorial Hospital, 222 Mei-King Road, Keelung 20448, Taiwan. E-mail address:
[email protected]. 0929-6646/$ - see front matter Copyright ª 2012, Elsevier Taiwan LLC & Formosan Medical Association. All rights reserved. doi:10.1016/j.jfma.2011.06.017
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Y.-Y. Chien 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. Copyright ª 2012, Elsevier Taiwan LLC & Formosan Medical Association. All rights reserved.
Introduction
DNA studies
OPMD is a late onset disorder of muscle; it is associated with progressive eyelid ptosis, dysarthria, dysphagia and proximal weakness.1,2 The cardinal pathologic findings of OPMD are the presence of distinctive muscle fibers containing rimmed-vacuoles under a light microscope (LM) and of unique myocyte nuclei containing tubulofilamentous-inclusion under an electron microscope (EM).3 This disorder can be transmitted as both autosomal dominant and recessive trait; mutations in the polyadenylate-binding protein nuclear 1 (PABPN1) gene have been incriminated.4,5 In 1915, Taylor first reported a French-Canadian family of progressive dysphagia with ptosis.6 In 1962, Victor et al first introduced the term oculopharyngeal muscular dystrophy to describe the same disorder of a North American Jewish family of eastern European origin.7 Subsequently, OPMD was reported worldwide; however, the frequency of this disease varies considerably from area to area. For instance, the prevalence of OPMD ranges from 0.5 to 1/100,000 population in European countries8 and reaches 100/100,000 French Canadians in Quebec.9 Likewise, the world’s highest gene frequency of OPMD, which reaches 1/600 population, was found in Israel’s Bukharan Jews emigrating from central Asia.10 In contrast, the incidence of OPMD may be lower, or rather underestimated, among Asian and African ethnicities than among Caucasian, as only a few reports have been published.11,12 This paper reports a male patient, emigrating from the southeastern part of China and settling down in southern Taiwan in 1949, who had progressive proximal weakness, ptosis, and dysphagia. Two of his daughters also had weakness and dysphagia. The pattern of inheritance, age of onset, muscle pathology findings, and the result of genetic analysis are compatible with those seen in OPMD. This is a China-born Chinese patient with genetically and pathologically proven OPMD.
Genomic DNA was extracted from white blood cells. The GCN repeat region of the PABPN1 gene was amplified by a PCR method provided by Brais et al13 and modified by Minami et al.14 The PCR product was subjected to ABI 310 Genetic Analyzer (Applied Biosystems, Carlsbad, California USA), and the fragment size in the base pair was analyzed by GeneScan software. GCN repeat size was determined by comparing the fragment size between the subjected patient and a series of reference samples in which precise GCN repeat sizes had already known by sequence analysis.
Review of the literature with focus on patients’ or first authors’ country of origin A total of 340 English papers about OPMD were obtained by using the PubMed search engine after entering the term “oculopharyngeal muscular dystrophy”. Being obviously irrelevant to the human OPMD, 18 of these 340 papers were excluded. The remaining 322 papers were categorized according to the patients’ country of origin or the first author’s if the patient’s information was not available. Horizontal stacked bar charts were drawn, with the length of each bar being proportioned to the number of paper the country published. Countries are categorized into groups according to the continent to which it belonged. Data were further expressed by the number of papers/10 million population of the country.
Patients and methods We examined 3 affected patients in a Chinese immigrant family shown in Fig. 1. All had mild proximal weakness and dysphagia. Electromyography (EMG), nerve conduction studies (NCS) and open muscle biopsies were performed in the proband (patient 1). Serial frozen sections were stained with H&E, modified Gomori trichrome and a battery of histochemical methods. The specimens for EM were fixed in 2% glutaraldehyde for 2 hours and then processed for embedding in epon. Semithin epon sections for LM were stained with toluidine blue, and ultrathin epon sections for EM were stained with uranly acetate and lead citrate.
Figure 1 Family Pedigree. Arrow indicates proband (PT1), PT2 Z patient 2, PT3 Z patient 3. Symbols represent the following: number Z age, square Z male, circle Z female, square/circle filled with color Z affected with dysphagia or ptosis.
A Chinese OPMD proven pathologically and genetically
Results Clinical manifestations and pathologic features All three patients of the proband’s family had mild proximal weakness and mild dysphagia. The oldest patient, the proband, had ptosis. According to the proband’s statement, his elder brother who remained in China, also had ptosis, dysphagia and weakness, but the medical history of the proband’s birth parents were not available. Two of the proband’s daughters, patients 2 and 3, now aged 46 and 38 years old, had only mild proximal weakness and mild dysphagia, but no ptosis (Fig. 1). The disorder appears to be inherited through an autosomal dominant trait.
Patient 1 (the proband) The proband was a 67-year-old male, the third of three siblings, who developed bilateral ptosis with no diurnal variation or diplopia at the age of 58 years. To compensate ptosis, he contracted the frontalis muscle and tilted the head backward (Fig. 2). Almost at the same time, he also suffered from episodic choking once or twice a week, with nasal regurgitation of food; this led to an endoscopic exam, but no remarkable findings were obtained. He did not lose weight. On manual muscle testing at the age of 62 years, he had only mild proximal weakness. Tendon reflexes were symmetrically normal and the plantar responses were flexor. He had neither cataracts nor retinal degeneration. His serum CK level was normal and cardiac evaluation showed no abnormality. Motor/sensory nerve conduction velocity and F-wave latencies were normal. The EMG studies of limb muscles showed a myopathic change, with slightly increased numbers of small polyphasic potentials in the abductor pollicis brevis, triceps brachii and paraspinal muscles at C6, T4 and L5 levels. There was no spontaneous activity in all examined muscles. He had a biopsy of the left biceps brachii at 62 years of age. In transverse sections of frozen specimens, there was mild variation in fiber size measuring from 5 to 80 mm in diameter (average Z 60 mm). No group atrophy, increase in number of internal nuclei, large centrally placed nuclei, pyknotic nuclear clumps, fiber splitting, necrotic fiber,
399 inflammatory response, or fibrosis were recognized. Small angulated fibers (about 4.9% of muscle fibers) with high oxidative enzyme activities, scattered throughout the specimen; some of these fibers contained rimmed vacuoles. These vacuoles, observed in about 0.12% of muscle fibers, consisted of irregularly round or polygonal clear spaces lined by a ring of material which was basophilic with HE stain and red with modified Gomori trichrome stain (Fig. 3A and 3B). In semithin epoxy sections, stained with toluidine blue, some nuclei appeared lighter than normal; on ultrathin sections, stained with uranyl acetate and lead citrate, some of these nuclei filled with filamentous inclusions (Fig. 4). The other EM findings were nonspecific myopathic alterations including: (1) myofibrillary degeneration with Zline streaming in atrophic fibers; (2) myeloid bodies, membranous structures, and cell debris in rimmed vacuoles; and (3) lipofuscin deposits. Genetic analysis for the expansion of the trinucleotide (GCG) repeat at 50 end of the coding region of the PABPN1 gene showed that the PCR products of the size corresponding to (GCN) 10 and (GCN) 13 were detected.
Patient 2 This 46-year-old female, the proband’s daughter and the first of six siblings, was not aware of any problem until her father was diagnosed as having OPMD. In the past, she occasionally experienced nasal regurgitation while eating meals. On examination, she was a well-nourished female and all her trunk and limb muscles were normal except for mild ptosis. Her deep tendon reflexes were all normal. She did not receive any laboratory examination.
Patient 3 This 38-year-old female, the proband’s daughter and the fourth of six siblings, also had mild ptosis; she accepted only physical examination and her manual muscle testing was almost identical to that seen in patient 2. She also had mild dysphagia, which presented as intermittent nasal regurgitation.
Figure 2 Photographs of the proband showing characteristic face features of OPMD: bilateral ptosis, raised eyebrows, and wrinkled forehead (2A). Besides contracting the frontalis muscle, proband tilted his head backward, Hutchinson’s posture, to compensate for the limitation of visual field defect due to ptosis (2B).
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Figure 3 Cryostat sections of proband’s left biceps brachii showing rimmed vacuole (3A) and small angulated fibers (3B). (A) hematoxylin and eosin; (B) adenosin triphosphatase pH 4.6.
Literature review with focus on epidemiology Approximately 30 countries have published 322 papers about OPMD thus far (Fig. 5A). Indeed, 80% of these papers were contributed by occidental countries, and the United States is the most productive country among them. Likewise, German is the most productive country in Europe, and Japan in Asia. Moreover, the number of publications on this disease among countries of the Americas and Asia are quite unequal, when compared to those of European countries. For instance, publications are mainly concentrated in the United States and Canada in the Americas, and in Japan, Israel, and Taiwan15,16 in Asia. However, the publications among European countries are fairly proportioned, especially in the western European countries. Fig. 5A illustrates such a state of disequilibrium. In crude terms, the concentration of the paper distribution in some way reflects the prevalence of this disease. This reflection nevertheless is distorted by many factors, including the level of medical care and the population of the country. To minimize these distortions, the number of papers was, therefore, divided by the population of the corresponding country. The results again showed that the European countries have relatively approximate publications/10 million populations (Fig. 5B); in fact, the true prevalence
Figure 4 An electron micrograph from proband’s left biceps brachii muscle demonstrating tubular filamentous inclusions in a subsarcolemmal nucleus. Bar Z 400 nm.
rates in these European countries ranges between 0.5 and 1/100,000 populations. Bu contrast, also in the new stacked bar chart, Canada and Uruguay become the first two rankings in the Americas,2,17 and Israel and Sakha in Asia. All four of these countries have large OPMD clusters. Those are Canada’s French Canadians in Quebec, who have the world’s largest cluster of OPMD with a frequency of 1/1000 population; Southern Uruguay’s Canary Islands settlers, whose ancestors move to Uruguay between 1985 and 1900; Israel’s Bukhara Jewish, who have the world’s highest gene frequency with 1/600 population; and the Republic of Sakha’s Yakut people, who have a frequency of 1/11680 Yakut population, which is 10 to 20 times higher compared to European populations.8
Discussion This paper reports a China-born Chinese patient who was confirmed histopathologically, ultrastructurally, and genetically to have OPMD. With its onset late in life and its clinical features resembling some common aging disorders, OPMD is therefore easily neglected in many developing countries. However, this disorder has been reported from > 30 countries, since Taylor reported typical OPMD victims from a French-Canadian family in 1915. So far, > 300 English papers about OPMD have been published, and the occidental countries have contributed over 80% of them (Fig. 5A). This big difference between eastern and western countries in terms of paper distribution, leads to the impression that OPMD is a disease of the western world and that most of the victims of this disorder are racially white. However, in 1982, Japan reported a Mongoloid OPMD family; this is the first oriental paper about OPMD.18 Subsequently, Israel, in 1990, reported a large OPMD cluster in Bukharan Jews who originated from Central Asia.19 Lastly, in 2008, located in eastern Siberia, the Sakha Republic, a federal subject of Russia, was reported to have a very high OPMD prevalence rate in the Yakut population; the prevalence rate is 10e20 times higher compared to European populations.20 Still, the densely populated areas of Asia, especially China and India having about one third of the world’s population, contributed only a limited number of papers about OPMD. This phenomenon is not necessary to denote that the prevalence rates of OPMD in these areas
A Chinese OPMD proven pathologically and genetically
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Figure 5 Horizontal stacked bar chart showing the world distribution of publication of OPMD. (A) each bar represents the amount of paper the country published, and the country bars were stacked up according to the continent it belonged; (B) each country bar represents the amount of paper the country published divided the number of 10 million population the country has.
are extremely low; instead, it may just reflect that OPMD has been underdiagnosed there. The reason why OPMD has been underdiagnosed in the densely populated areas of Asia is threefold: firstly, OPMD is a rare disorder not well recognized by medical doctors in the developing countries of Asia; secondly, developed countries of these areas, such as Japan and Taiwan, readily diagnosed and reported cases of OPMD (Fig. 5); and thirdly, some countries outside China diagnosed and reported Chinese immigrants to have OPMD, indicating underdiagnosis of this disease in their motherland. Although large clusters of victims can be found, OPMD is so rare, as to be neglected by some popular neurologic text books. Besides, its cardinal clinical features, ptosis and dysphagia, are non-specific manifestations; thus, OPMD is easily misinterpreted as other aging disorders. Furthermore, an exact diagnosis of OPMD can only be made either by observing tubulofilamentous-inclusion in myocyte nuclei on EM, or demonstrating abnormal GCG repeat at the 5’ end of the coding region of PABPN1 gene on genetic analysis. The crucial diagnostic facilities of OPMD, EM and genetic analysis, are not widely available in developing countries. Consequently, the low OPMD report rate in densely populated areas of Asia may account for the low diagnostic rate of this disease, rather than the low prevalence rate. China, which accounts for 20% of the world’s population, has published only a few pathologically and genetically confirmed papers about OPMD.21e23 By contrast, Japan and Taiwan, having a relatively similar ethnic background to China but far better medical care facilities than China, have higher OPMD report rates than China. The report rates of these two countries are quite similar to those of European countries, despite the ethnic differences between East Asia and Europe (Fig. 5B). In fact, Japan’s OPMD report rate is even higher than that in the United States, and Taiwan’s is similar to Spain’s. Both the medical facilities and the OPMD report rate, are at the same level between Europe, Japan and Taiwan; thus, the prevalence of OPMD in East Asia may be higher than previously expected. Moreover, two large OPMD clusters located in places near China, are Bukhara Jews in Uzbekistan near China’s western border and Yakut people in the Sakha Republic near China’s northern border. For these reasons, China’s OPMD prevalence rate may be higher than previously expected. At least three reports contributed by China’s next-door neighbors, Singapore in 1992,24 Malaya in 2005,25 and Taiwan (the present report), show clear evidence that
Chinese immigrants, originally from southern China, have OPMD. Despite all of these hard facts, China published only three papers about OPMD. Thus, it is highly suspected that OPMD in China, especially in Southern China, is underdiagnosed. To sum up, reasons for the very low OPMD report rate in developing countries of East Asia include the unfamiliarity of medical workers to this rare disorder, and the unavailability of medical supplies to confirm the diagnosis. In addition, there is clear evidence indicating that OPMD in these areas is underdiagnosed.
Acknowledgments The author would like to thank the family for their participation, Drs Narihiro Minami and Ichizo Nishino, Department of Neuromuscular Research, National Institute of Neuroscience, Tokyo, Japan, for performing the DNA analyses.
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