ORIGINAL PAPER

Oculopharyngeal Muscular Dystrophy: Phenotypic and GenotypicStudies in a Chinese Population

Jingli Shan • Bin Chen • Pengfei Lin •

Duoling Li • Yuebei Luo • Kunqian Ji •

Jinfan Zheng • Yun Yuan • Chuanzhu Yan

Received: 26 April 2014 / Accepted: 9 September 2014 / Published online: 5 October 2014

� Springer Science+Business Media New York 2014

Abstract 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 char-

acteristics 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 het-

erozygote 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.

Keywords Oculopharyngeal muscular dystrophy �OPMD � PABPN1 � (GCN) expansion

Introduction

Oculopharyngeal muscular dystrophy (OPMD) is a late-

onset neuromuscular disorder characterized by progressive

ptosis, dysphagia, and proximal muscle weakness, with

unique nuclear filament inclusions in skeletal muscle fibers

as its pathological hallmark (Tome and Fardeau 1980). The

underlying cause is the abnormal (GCN) expansion or, more

rarely, point mutations leading to a lengthening of the tract in

exon 1 of the polyadenylate-binding protein nuclear 1 gene

(PABPN1) on chromosome 14q11 (Brais et al. 1998; Rob-

inson et al. 2006). The normal allele is (GCG)6(GCA)3

(GCG)1 encoding 10 alanines (Ala10) (Brais et al. 1998).

Jingli Shan and Bin Chen have contributed equally to this work.

Electronic supplementary material The online version of thisarticle (doi:10.1007/s12017-014-8327-5) contains supplementarymaterial, which is available to authorized users.

J. Shan � P. Lin � D. Li � K. Ji � J. Zheng � C. Yan

Laboratory of Neuromuscular Disorders and Department of

Neurology, Qilu Hospital, Shandong University, Jinan 250012,

China

B. Chen

Department of Neurology, Beijing Tiantan Hospital,

Beijing 100050, China

Y. Luo

Center for Neruomuscular and Neurological Disorders,

Australian Neuro-Muscular Research Institute, University of

Western Australia, Perth 6007, Australia

Y. Yuan (&)

Department of Neurology, Peking University First Hospital,

8 Xishiku St, Xicheng District, Beijing 100034, China

e-mail: yuanyun2002@126.com

C. Yan (&)

Key Laboratory for Experimental Teratology of the Ministry of

Education, Brain Science Research Institute, Shandong

University, Jinan 250012, China

e-mail: chuanzhuyan@163.com

123

Neuromol Med (2014) 16:782–786

DOI 10.1007/s12017-014-8327-5

PABPN1 variants were first described as pure (GCG)

expansions of the normal (GCG)6 stretch (Brais et al. 1998).

Subsequently, additional (GCA) interspersions within

(GCG) expansions were reported in various populations

(Muller et al. 2006; Nakamoto et al. 2002). Now, (GCN)12–17

has been widely accepted as the autosomal dominant form

(Brais 2009). The extremely uncommon autosomal recessive

form of OPMD has been shown to result from the homozy-

gosity of (GCN)11 expansion, which was referred to as

(GCG)7 previously (Brais et al. 1998). This (GCN)11 poly-

morphism, with a prevalence of 1–2 % in North America,

Europe, and Japan, is also considered as a phenotype modi-

fier (Brais 2009; Brais et al. 1998).

OPMD has a worldwide distribution, particularly pre-

valent in the French Canadian population (1:1,000) and in

Bukhara Jews living in Israel (1:600) (Brais 2009). The

clusters of OPMD cases identified in various populations

recently make it possible to explore the phenotype–geno-

type correlation. However, OPMD appears to be sparse

among East Asians, with most families being reported in

Japan (Uyama et al. 1996, 1997; Nagashima et al. 2000;

Nakamoto et al. 2002). Thus far, only rare cases have been

reported in mainland China (You et al. 2010; Ye et al.

2011). Taiwan, sharing a similar genetic background, has a

higher prevalence rate (Kuo et al. 2009; Huang et al. 2010).

Additionally, at least 3 Chinese immigrants, originally

from southern China, have been reported to have OPMD

(Lim et al. 1992; Goh et al. 2005; Ruegg et al. 2005).

Therefore, it has been suspected that OPMD is being

under-diagnosed in mainland China. Here, we report the

clinical and genetic characteristics of 34 OPMD patients

from 13 unrelated families in northern China.

Materials and Methods

All 34 subjects from 13 unrelated families were recruited

through the Neurology department of Qilu Hospital of

Shandong University and Peking University First Hospital.

All probands and some of their relatives were analyzed for

(GCN) expansion in exon 1 of the PABPN1 gene by

Kingmed Diagnostics, Guangzhou, according to standard

protocol (Jiahui et al. 2005), and each of them carried an

expanded (GCN) repeat.

Nerve conduction studies (NCS) and needle electromy-

ography (EMG) were performed in 10 of 13 probands.

Repetitive nerve stimulation (RNS) test was performed in 8

probands. Muscle biopsy was carried out in probands from

each family under local anesthesia. Muscle specimens for

histological examination were frozen in isopentane that

was precooled in liquid nitrogen and stored at -80 �C.

Serial frozen Sects. (8 lm) were stained with hematoxylin

and eosin (H & E), modified Gomori trichrome,

nicotinamide adenine dinucleotide tetrazolium dehydroge-

nase, succinate dehydrogenase, cytochrome c oxidase, oil

red O, periodic acid Schiff, and adenosine triphosphatase

(ATPase; pH 4.3, 4.6, and 10.8). Muscle specimens from 4

probands were prepared for electron microscopy. These

specimens were fixed in ice-cold glutaraldehyde and

osmium tetroxide successively. After rapid dehydration in

graded series of acetone, tissue blocks were embedded in

Epon. Thin sections (1 lm) of the embedded blocks were

stained with uranyl acetate and lead citrate and examined

by transmission electron microscopy.

Results

Genetic Analysis

Genetic analysis of 13 unrelated families revealed pure

(GCG) expansions of the PABPN1 gene in 10 families;

specifically, we saw (GCG)8 in 1 family, (GCG)9 in 6

families, (GCG)10 in 2 families, and (GCG)11 in 1 family.

We detected (GCA) triplet interspersions in 3 families. The

(GCG)6(GCA)1(GCG)3(GCA)3(GCG)1 allele was found in

2 families. In another family shown in Fig. 1 (family 1),

the proband was a compound heterozygote with (GCG)6

(GCA)1(GCA)3(GCG)1/(GCG)6(GCA)1(GCG)1(GCA)3

(GCG)1. Her elder sister had one normal allele and the

mutated allele of (GCG)6(GCA)1(GCG)1(GCA)3(GCG)1.

Her younger brother, who carried the (GCG)6(GCA)1

(GCA)3(GCG)1 allele, was asymptomatic and was not

included in subsequent phenotypic summary. All genotypes

were summarized in Table 1.

Clinical Presentations

Out of 34 cases in our cohort, 19 were male and 15 were

female. The mean age at onset was 47.2 ± 11.2 years

(range 27–67 years). The mean disease duration was

15.5 ± 12.6 years (range 1–53 years) at the time of the last

examination.

Dysphagia was the most common initial symptom (18/

34), with the mean age at the onset of 44.8 ± 10.7 years.

Ptosis was the initial symptom in 9 out of 34 cases, with the

mean age at the onset of 57.8 ± 7.7 years. Two patient

presented with both symptoms at onset. Additionally, two

had dysarthria, two had both dysphagia and dysarthria, and

one had limb muscle weakness initially. There was a sig-

nificant difference between the age at onset in the dysphagia

group and that in the ptosis group as studied by Mann–

Whitney U test (p = 0.0036).

During the course of the disease, 30 of 34 cases suffered

from dysphagia, mainly presenting as prolonged meal time.

None of our patients needed nasogastric tube feedings.

Neuromol Med (2014) 16:782–786 783

123

Twenty-seven of 34 cases had ptosis as the disease progressed,

with visual impairment caused by the ptosis being the main

complaint in our cohort. One patient underwent levator

resection, but ptosis recurred 2 years after the surgery. Oph-

thalmoplegia was present in 18 out of 34 cases, with the

involvement of superior rectus being the most common.

Markedly limited eye movement in all directions was present

in only one patient. Fourteen patients had predominantly

proximal limb weakness, and 9 of them had mild distal muscle

involvement along with the disease’s progression. All these

cases were ambulatory at the last visit. Sixteen patients aged

between 54 and 79 years, with the mean disease duration of

10.8 ± 9.4 years (range 1–29 years), had no limb muscle

weakness. Four patients had no limb muscle weakness until

they died of unrelated causes, at the age of 68–71.

Four families with more than 3 patients (family 2, 3, 4,

and 5) showed intrafamilial homogeneity to a great extent

on initial symptom and occurrence of limb muscle weak-

ness (Online Resource 1). As for patient IV6 from family 3

and patient III1 and III2 from family 5, the absence of limb

muscle weakness may be due to the early stage they were

in (Online Resource 1). In family 1, the proband with

(GCN)11/(GCN)12 had dysphagia and subsequently ptosis

at the age of 53, then developed lower limb weakness at the

age of 54, whereas her sister with (GCN)10/(GCN)12 pre-

sented with dysphagia at the age of 57, which was the only

symptom until the last examination (Online Resource 1).

Other Investigations

Serum creatine kinase levels that were measured in 21

cases ranged from normal values to 3.7-fold of the upper

normal limit. Electrophysiological studies were performed

in 10 probands (Online Resource 2). Only 1 patient showed

mildly decreased conduction velocity in NCS, with normal

latency, compound muscle action potential, and sensory

nerve action potential. Needle EMG revealed a normal

pattern in 4 cases, myogenic changes in 4 cases, neurogenic

changes in 1 case, and a myogenic/neurogenic mix pattern

in 1 case. RNS tests in 8 of the cases were normal. Muscle

biopsies performed in 13 probands at different disease

Fig. 1 a The pedigree of family 1. b The genotypes of members in family

1 were (GCG)6(GCA)1(GCA)3(GCG)1/(GCG)6(GCA)1(GCG)1(GCA)3

(GCG)1 in the proband II2, (GCN)10/(GCG)6(GCA)1(GCG)1(GCA)3

(GCG)1 in II1 and (GCN)10/(GCG)6(GCA)1(GCA)3(GCG)1 in II3. The

lowest one was a normal control with (GCN)10/(GCN)10

Table 1 Genotypes of PABPN1 in the analyzed population

Genotype Total alanine

codons/(GCN)

No. of

families

Normal sequence

(GCG)6(GCA)3(GCG)1 10

Pure (GCG) expansion

(GCG)8(GCA)3(GCG)1 12 1

(GCG)9(GCA)3(GCG)1 13 6

(GCG)10(GCA)3(GCG)1 14 2

(GCG)11(GCA)3(GCG)1 15 1

Expansion with (GCA) interspersion

(GCG)6(GCA)1(GCA)3(GCG)1 11 1a

(GCG)6 (GCA)1(GCG)1(GCA)3(GCG)1 12 1a

(GCG)6 (GCA)1(GCG)3(GCA)3(GCG)1 14 2

a This family includes one compound heterozygote with (GCG)6

(GCA)1(GCA)3(GCG)1/(GCG)6(GCA)1(GCG)1(GCA)3(GCG)1

784 Neuromol Med (2014) 16:782–786

123

stages revealed myopathic changes with rimmed vacuoles.

The mean frequency of rimmed vacuoles was 1.7 %. By

electron microscopy, intranuclear inclusions formed by

tubular filaments were found in 3 of 4 probands (Fig. 2).

Discussion

Analysis of the PABPN1 gene in our cohort revealed 7

different expansion types, with (GCG)6(GCA)1(GCA)3

(GCG)1 being first described here. Although cryptic

(GCN)11 has been widely referred to as the polymorphic

allele, to the best of our knowledge, no (GCA) insertion has

been reported before. The genetic heterogeneity implies

multiple founders in Chinese population. Similar situation

has been depicted in UK and German populations (Rob-

inson et al. 2005; Muller et al. 2006). The genotypes with

(GCA) interspersions, found in 3 families, further support

the theory that unequal crossing over is the causative

molecular mechanism leading to OPMD.

Phenotypically, dysphagia was the most common initial

symptom in our cohort, while ptosis was the most common

initial symptom in the previous large-scale studies (Mira-

bella et al. 2000; Hill et al. 2001; Tondo et al. 2012). A

possible reason for this observation is the eyelid anatomical

variation in different ethnic groups. Asian eyelids have a

distinctive appearance with a narrower palpebral fissure, a

lower or absent lid crease, and a greater fullness in upper

lids, compared with that of the Caucasians (Liu and Hsu

1986; Kim and Bhatki 2005). Such features in Asians may

make ptosis less obvious, giving rise to the unawareness of

an insidious onset of ptosis. However, further support based

on large-scale studies in Asian groups is needed.

Additionally, the low education level of our patients may

also contribute to the unawareness. A simple stochastic

incident due to the small sample is still possible. OPMD

could not be excluded simply by the absence of ptosis, since

Hill et al. also reported 23 % of patients presented with

dysphagia initially (Hill et al. 2001). Another interesting

finding in our cohort is that the patients in the dysphagia

group had a much earlier onset compared with those in the

ptosis group, which is in accordance with the finding in the

Spanish population (Tondo et al. 2012). As for the corre-

lation between severity of the disease and the length of the

repeats, no conclusion could be drawn based on our

patients. However, intrafamilial homogeneity was noticed,

which further suggests that other genetic background apart

from the already known genotype could modulate the age at

onset and the presentation of some symptoms.

Brais et al. first speculated that the (GCN)11 polymor-

phism might have disease-modifying effects, in that a

compound heterozygote with (GCN)11/(GCN)13 displayed a

more severe disease phenotype than a sibling with (GCN)10/

(GCN)13 (Brais et al. 1998). Subsequently, Hill et al.

described a compound heterozygote sibling pair with

(GCN)11/(GCN)12 who had a much earlier onset than

unrelated subjects with (GCN)10/(GCN)12 (Hill et al. 2001).

Such situations are in line with what we observed in our

family 5 (Online Resource 1). However, such compound

heterozygotes in the Italian population did not appear to

have a more severe phenotype or an earlier onset (Mirabella

et al. 2000). Further data are required to clarify the role of

(GCN)11 polymorphism in modifying the phenotype.

In conclusion, our data confirm the spectrum of geno-

types reported in OPMD and support the theory of unequal

crossing over. The heterogeneous genetic basis of OPMD

implies that there is no single founder effect in Chinese

population. Our data also lend support to the point that

(GCN)11 polymorphism may have a disease-modifying

effect. Finally, phenotypic intrafamilial homogeneity

observed in our series suggests that other genetic factors

may contribute to the modification of the phenotype.

Acknowledgments We thank the patients and their families for

their participation. We thank Alyssa Nylander (Neurology Depart-

ment, Yale School of Medicine, Yale University, CT, USA) for

careful review of the grammar in our manuscript. This work was

supported by China Postdoctoral Science Foundation and Doctoral

Fund of Ministry of Education of China.

Conflict of interest The authors declare that they have no conflict

of interest.

Ethical standard Samples from patients were obtained in accor-

dance with the Helsinki Declaration of 1964, as revised in 2000, and

with the appropriate signed informed consent. The study was

approved by the Ethical Committee of Shandong University and

Peking University.

Fig. 2 Tubulofilamentous inclusions in the nucleus marked with

arrow (lead citrate and uranyl acetate staining, 920,000)

Neuromol Med (2014) 16:782–786 785

123

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