Oculopharyngeal Muscular Dystrophy: Phenotypic and Genotypic Studies in a Chinese Population
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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
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. YanLaboratory of Neuromuscular Disorders and Department of
Neurology, Qilu Hospital, Shandong University, Jinan 250012,
Department of Neurology, Beijing Tiantan Hospital,
Beijing 100050, China
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
C. Yan (&)Key Laboratory for Experimental Teratology of the Ministry of
Education, Brain Science Research Institute, Shandong
University, Jinan 250012, China
Neuromol Med (2014) 16:782786
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)1217has 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 12 % 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 phenotypegeno-
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 hematoxylinand 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 werestained with uranyl acetate and lead citrate and examined
by transmission electron microscopy.
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.
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 2767 years). The mean disease duration was
15.5 12.6 years (range 153 years) at the time of the last
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) 16:782786 783
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 diseases 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 129 years), had no limb muscle
weakness. Four patients had no limb muscle weakness until
they died of unrelated causes, at the age of 6871.
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).
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 family1 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
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) 16:782786
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).
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...