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.     

眼咽型肌营养不良汉族六家系的临床和遗传学特点

目的 初步总结我国汉族眼咽型肌营养不良(OPMD)患者的临床和多腺苷酸结合蛋白核1(PABPN1)基因改变特点.方法 6个OPMD家系共28例患者,男性13例,女性15例,发病年龄32～70岁,平均发病年龄49.7岁.在可确定首发症状的患者中,以吞咽困难或构音障碍首发的13例、眼睑下垂首发的4例、双下肢无力首发的1例.经过3～20年均出现眼睑下垂、吞咽困难和构音障碍,其中7例出现四肢近端无力.对6例先证者做肌肉活体组织检查,标本进行常规组织病理和电镜检查.对6个家系的先证者以及部分家庭成员进行PABPN1基因检查,并对6例先证者进行单体型分析.结果 6例先证者的肌肉活体组织检查均发现肌纤维直径轻度变异加大伴随肌纤维内镶边空泡形成,4例患者经电镜检查发现OPMD典型的核内栅栏样丝状包涵体.3个家系的PABPN1基因型为(GCG)9,另外3个家系的基因型分别为(GCG)6(GCA)1(GCG)3、(GCG)10和(GCG)8.2个携带(GCG)9突变的家系存在rs2239579(C)-(GCG)9-SNP2622(C)的单倍体型.结论 吞咽异常和眼睑下垂均是我国汉族OPMD患者的首发症状.肌纤维出现镶边空泡以及核内包涵体是我国患者的常见病理改变.PABPN1基因的(GCG)异常扩增和(GCA)插入突变均出现在我国患者,起源具有多源性.携带(GCG)9突变的部分家系可能来自共同祖先.     

Progress in understanding the pathogenesis of oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is an adult-onset disorder characterized by progressive eyelid drooping (ptosis), swallowing difficulties (dysphagia), and proximal limb weakness. The autosomal dominant form of this disease is caused by expansions of a (GCG)6 repeat to (GCG)8-13 in the PABPN1 gene. These mutations lead to the expansion of a polyalanine stretch from 10 to 12-17 alanines in the N-terminal domain of PABPN1. Mutated PABPN1 (mPABPN1) induces the formation of muscle intranuclear inclusions that are thought to be the hallmark of this disease. In this review, we discuss: 1) OPMD genetics and PABPN I function studies; 2) diseases caused by polyalanine expansions and cellular polyalanine toxicity; 3) mPABPN1-induced intranuclear inclusion toxicity; 4) role of oligomerization of mPABPNI in the formation and toxicity of OPMD intranuclear inclusions and; 5) recruitment of subcellular components to the OPMD inclusions. We present a potential molecular mechanism for OPMD pathogenesis that accounts for these observations.     

Variability of the recessive oculopharyngeal muscular dystrophy phenotype

Oculopharyngeal muscular dystrophy (OPMD) is usually transmitted as an autosomal-dominant trait and characterized by an expansion from 6 to 8 or more GCG/GCA repeats in the poly-(A) binding protein nuclear 1 (PABPN1) gene on chromosome 14q11. Autosomal-recessive OPMD with a homozygous (GCG)7 expansion of PABPN1 has only been described in two Canadian patients, who showed a comparably mild phenotype, suggesting that it is less severe than the dominant form. We clinically and genetically characterized the first two reported cases of autosomal-recessive OPMD in Europe. Remarkably, both patients revealed severe and diverse phenotypes, with an unusual onset and atypical clinical course in one patient. Former studies found a 1%-2% frequency of the (GCG)7 allele, which theoretically produces an incidence of 1:10,000 of autosomal-recessive OPMD in the general population. We conclude that the apparent rarity of the autosomal-recessive form of OPMD may be due to the fact that genetic testing is generally administered only to patients with typical clinical features or a positive family history.     

Identification of a novel mutation in a Korean patient with oculopharyngeal muscular dystrophy.

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset muscle disorder characterized by progressive dysphagia and bilateral ptosis. Mutations in the polyadenylate binding protein nuclear 1 (PABPN1) gene have been found to cause OPMD. The typical mutation is a stable trinucleotide repeat expansion in the first exon of the PABPN1 gene, in which (GCG)(6) is the normal repeat length. We investigated a Korean patient with OPMD and identified a novel mutation: a heterozygous insertion of a 9-bp sequence [(GCG)(GCA)(GCA); c.27_28insGCGGCAGCA] instead of the (GCG) repeat expansion, resulting in an in-frame insertion of three alanines (p.A10insAAA). To the best of our knowledge, this is the first report of a genetically confirmed case of OPMD in Korea.     

Oculopharyngeal muscular dystrophy: A polyalanine myopathy

It has been 10 years since the identification of the first PABPN1 gene (GCN)_n/polyalanine mutations responsible for oculopharyngeal muscular dystrophy (OPMD). These mutations have been found in most cases of OPMD diagnosed in more than 35 countries. Sequence analyses have shown that such mutations have occurred numerous times in human history. Although PABPN1 was found early on to be a component of the classic filamentous intranuclear inclusions (INIs), mRNA and other proteins also have been found to coaggregate in the INIs. It is still unclear if the INIs play a pathologic or a protective role. The generation of numerous cell and animal models of OPMD has led to greater insight into its complex molecular pathophysiology and identified the first candidate therapeutic molecules. This paper reviews basic and clinical research on OPMD, with special emphasis on recent developments in the understanding of its pathophysiology.     

Oculopharyngeal muscular dystrophy with PABPN1 mutation in a Chinese Malaysian woman

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant disorder of middle age presenting as progressive dysphagia and eyelid ptosis, due to short expansions of the GCG trinucleotide repeat (from GCG6 to GCG8-13) in the polyadenylate binding-protein nuclear 1 (PABPN1) gene. OPMD is rarely seen in Asians and morphologically and/or genetically confirmed cases have been reported in Japanese kindreds only. We report a 64 year old Chinese-Malaysian woman who presented with progressive dysphagia and bilateral ptosis for about 6 years. Her mother and elder brother (both deceased) were believed to be affected. Muscle histopathology revealed angulated fibres with rimmed vacuoles. Genetic analysis showed repeat expansion in one allele to (GCG)9 while normal in the other (GCG)6. This is the first non-Japanese Asian family with genetically confirmed OPMD.     

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.     

HnRNP A1 and A/B interaction with PABPN1 in oculopharyngeal muscular dystrophy

BACKGROUND: Oculopharyngeal muscular dystrophy (OPMD) is an adult-onset disorder characterized by progressive ptosis, dysphagia and proximal limb weakness. The autosomal dominant form of this disease is caused by short expansions of a (GCG)6 repeat to (GCG) in the PABPN1 gene. The mutations lead to the expansion of a polyalanine stretch from 10 to 12-17 alanines in the N-terminus of PABPN1. The mutated PABPN1 (mPABPN1) induces the formation of intranuclear filamentous inclusions that sequester poly(A) RNA and are associated with cell death. METHODS: Human fetal brain cDNA library was used to look for PABPNI binding proteins using yeast two-hybrid screen. The protein interaction was confirmed by GST pull-down and co-immunoprecipitation assays. Oculopharyngeal muscular dystrophy cellular model and OPMD patient muscle tissue were used to check whether the PABPN1 binding proteins were involved in the formation of OPMD intranuclear inclusions. RESULTS: We identify two PABPNI interacting proteins, hnRNP A1 and hnRNP A/B. When co-expressed with mPABPN1 in COS-7 cells, predominantly nuclear protein hnRNP A1 and A/B co-localize with mPABPN1 in the insoluble intranuclear aggregates. Patient studies showed that hnRNP A1 is sequestered in OPMD nuclear inclusions. CONCLUSIONS: The hnRNP proteins are involved in mRNA processing and mRNA nucleocytoplasmic export, sequestering of hnRNPs in OPMD intranuclear aggregates supports the view that OPMD intranuclear inclusions are "poly(A) RNA traps", which would interfere with RNA export, and cause muscle cell death.     

Soluble expanded PABPN1 promotes cell death in oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant disease caused by the expansion of a polyalanine repeat (GCG)(8-13) in exon 1 of the PABPN1 gene. Skeletal muscle fibers nuclei from OPMD patients contain insoluble polyalanine expanded PABPN1 (expPABPN1) nuclear aggregates that sequester different cellular components. Whether these aggregates are pathogenic, or the consequence of a molecular defense mechanism, remains controversial in the field of neurodegenerative disorders and OPMD. Our cellular model shows that interfering with the formation of expPABPN1-induced large nuclear aggregates increases the availability of nuclear expPABPN1 and significantly exacerbates cell death. Live microscopy reveals that cells harboring an increased amount of the soluble forms of expPABPN1 are significantly more prone to toxicity than those with nuclear aggregates. This is the first report directly indicating that nuclear aggregation in OPMD may reflect an active process by which cells sequester and inactivate the soluble toxic form of expPABPN1.     

Unequal crossing-over in unique PABP2 mutations in Japanese patients: a possible cause of oculopharyngeal muscular dystrophy

BACKGROUND: Oculopharyngeal muscular dystrophy (OPMD) is an adult-onset autosomal dominant muscle disease with a worldwide distribution. Recent findings reveal the genetic basis of this disease to be mutations in the polyA binding-protein 2 (PABP2) gene that involve short expansions of the GCG trinucleotide repeat encoding a polyalanine tract. The underlying mechanism causing the triplet-expansion mutation in PABP2 remains to be elucidated, although the DNA slippage model is thought to be a plausible explanation of that. METHODS AND RESULTS: We analyzed PABP2 using polymerase chain reaction analysis and DNA sequencing in Japanese patients with pathologically confirmed OPMD, and found mutated (GCG)(6)GCA(GCG)(3)(GCA)(3)GCG and (GCG)(6)(GCA)(3)(GCG)(2)(GCA)(3)GCG alleles instead of the normal (GCG)(6)(GCA)(3)GCG allele. These mutated alleles could be explained by the insertions or duplications of (GCG)(3)GCA and (GCG)(2)(GCA)(3), respectively, but not by the simple expansion of GCG repeats. The clinical features of our patients were compatible with those of other Japanese patients carrying PABP2 that encodes a polyalanine tract of the same length, but were not compatible with those of Italian patients. CONCLUSIONS: The mutated alleles identified in our Japanese patients with OPMD were most likely due to duplications of (GCG)(3)GCA and (GCG)(2)(GCA)(3) but not simple expansions of the GCG repeats. Therefore, unequal crossing-over of 2 PABP2 alleles, rather than DNA slippage, is probably the causative mechanism of OPMD mutations. All mutations that have been reported in patients with OPMD so far can be explained with the mechanism of unequal crossing-over. On the other hand, comparison of the clinical features of our patients with those of other patients in previous reports suggests that specific clinical features cannot be attributed to the length of the polyalanine tract per se.     

Premature proliferative arrest of cricopharyngeal myoblasts in oculo-pharyngeal muscular dystrophy: Therapeutic perspectives of autologous myoblast transplantation

Cultures of myoblasts isolated from cricopharyngeal muscles from patients with oculopharyngeal muscular dystrophy (OPMD) have been performed to study the effect of the expanded (GCG)8-13 repeat, located on the poly(A) binding protein nuclear-1 (PABPN1), on satellite cell phenotype. Cell cultures exhibited a reduced myogenicity, as well as a rapid decrease in proliferative lifespan, as compared to controls. The incorporation of BrdU decreased during the proliferative lifespan, due to a progressive accumulation of non-dividing cells. A lower fusion index was also observed, but myoblasts were able to form large myotubes when OPMD cultures were purified, although a rapid loss of myogenicity during successive passages was also observed. Myoblasts isolated from unaffected muscles did not show the defects observed in cricopharyngeal muscle cultures. The PABPN1 was predominantly located in nuclei of myoblasts and in both the nuclei and cytoplasm of myotubes in OPMD cultures. In vivo analysis of OPMD muscles showed that the number of satellite cells was slightly higher than that observed in age matched controls. Mutation of the PABPN1 in OPMD provokes premature senescence in dividing myoblasts, that may be due to intranuclear toxic aggregates. These results suggest that myoblast autografts, isolated from unaffected muscles, and injected into the dystrophic pharyngeal muscles, may be a useful therapeutic strategy to restore muscular function. Its tolerance and feasibility has been preclinically demonstrated in the dog.     

Evaluation of the lumbar and ventricular infusion test in the diagnostic strategy of pediatric hydrocephalus and the therapeutic implications

Aim To evaluate the infusion test as a diagnostic tool behind the choice of intervention in pediatric hydrocephalus.Materials and methods Intracranial pressure (ICP) measurement and infusion test were performed intraventricularly, by lumbar route, or combined in 40 consecutive children as a part of the standard diagnostic program in 1996–1999.Results The median age was 18.5 months, ranging from 2 weeks to 13 years. In the subgroup of patients with radiological aqueductal stenosis (N=14), mean lumbar/intraventricular ICP was 13 (3–35)/10 (2–27). Mean lumbar/ventricular R _out were 18 (4–49)/17 (6–37). For patients with radiological communication between the third and fourth ventricles (N=14), the mean lumbar/intraventricular ICP was 11 (7–17)/9 (1–16). Mean lumbar/ventricular R _out were 8 (3–11)/8 (4–12). A total of 13 patients had a shunt insertion, 10 had an endoscopic third ventriculostomy (ETV), 5 had endoscopic fenestration of a cyst, and 12 had no surgery. Of the patients initially treated with EVT, 50% had a shunt insertrion shortly after. For communicating hydrocephalus, 75% of the patients initially not operated based on normal R _out values ended up having a shunt insertion.Discussion R _out has doubtful value as an indicator for conducting an operation or not and in the choice between EVT and shunt in chiladren. This should be interpreted in the light of a growing understanding of hydrocephalus on a molecular level.     

A late-onset case of oculopharyngeal muscular dystrophy carrying a (GCG)8 repeat expansion in the PAPBN1 gene]

We report a sporadic case of a female patient with oculopharyngeal muscular dystrophy (OPMD). Her father died at age 86 and mother at age 74. There was no familial occurrence of the disease. The patient initially developed a nasal voice at age 66. Neurological examinations on admission at age 72 revealed bilateral ptosis, a limitation of ocular movement without diplopia, dysphagia, and proximal muscle weakness. Serum creatine kinase level was slightly increased. Biopsied muscle specimens showed variation in fiber size as well as the occasional presence of rimmed vacuoles. On the basis of these clinical and laboratory findings, we suspected a diagnosis of OPMD, although a family history was absent. To confirm the diagnosis of OPMD, we performed a gene analysis for poly A binding protein, nuclear 1 (PABPN1; PABP2), which revealed a mild expansion of GCG repeat (8 repeats) as a heterozygous state. Clinical features of the patient were consistent with those in a previous literature reporting that patients carrying (GCG)8 repeat as a heterozygous state show a relatively late onset and a mild phenotype. The case of this patient emphasizes the importance of the PABPN1 gene analysis for patients showing muscular weakness involving oculopharyngeal and proximal limb muscles even when a familial occurrence of the disease is not apparent.     

Unusual triplet expansion associated with neurogenic changes in a family with oculopharyngeal muscular dystrophy

The occasional observation of neurogenic features in oculopharyngeal muscular dystrophy (OPMD) is unclear both in nosological and in etiological respects. Studies are reported here of a family with autosomal‐dominant OPMD involving seven members over three generations. In three of them muscle biopsies were performed. Two of the patients (a 45‐year‐old sister and a 57‐year‐old brother of the third generation) were studied in more detail and, in addition to the typical changes of OPMD, showed a neurogenic component both by electrophysiology and morphology. Molecular genetic investigations revealed a repeat unit of (GCG/GCA)₁₃ in the first exon of the poly(A)binding‐protein2 gene in both siblings. A possible association of this unusually long triplet repeat extension with the atypical phenotype is considered and has to be verified in other cases.     

Transgenic expression of an expanded (GCG)13 repeat PABPN1 leads to weakness and coordination defects in mice

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset disorder caused by a (GCG)n trinucleotide repeat expansion in the poly(A) binding protein nuclear-1 (PABPN1) gene, which in turn leads to an expanded polyalanine tract in the protein. We generated transgenic mice expressing either the wild type or the expanded form of human PABPN1, and transgenic animals with the expanded form showed clear signs of abnormal limb clasping, muscle weakness, coordination deficits, and peripheral nerves alterations. Analysis of mitotic and postmitotic tissues in those transgenic animals revealed ubiquitinated PABPN1-positive intranuclear inclusions (INIs) in neuronal cells. This latter observation led us to test and confirm the presence of similar INIs in postmortem brain sections from an OPMD patient. Our results indicate that expanded PABPN1, presumably via the toxic effects of its polyalanine tract, can lead to inclusion formation and neurodegeneration in both the mouse and the human.     

GCG genetic expansions in Italian patients with oculopharyngeal muscular dystrophy

OBJECTIVE: To screen Italian patients with oculopharyngeal muscular dystrophy (OPMD) for GCG repeat expansions in the Poly(A) binding-protein 2 (PABP2) gene. BACKGROUND: Oculopharyngeal muscular dystrophy is an adult-onset autosomal dominant muscle disease linked to 14q11 pathologically characterized by unique 8.5 nm intranuclear filaments in skeletal muscle fibers. Short expansions of a (GCG)6 repeat located in exon 1 of the newly isolated PABP2 gene have been demonstrated in a large number of OPMD families. METHODS: We studied 18 patients diagnosed with OPMD. A muscle biopsy was performed in 16 patients. Screening for the pathologic expansion was performed on a PCR amplified DNA fragment encompassing the GCG repeat. RESULTS: Heterozygous (GCG)-repeat expansions were detected in 13 patients in association with (GCG)6 normal allele or (GCG)7 polymorphic allele. All the patients whose muscle biopsy showed typical 8.5 nm intranuclear filaments had a mutated PABP2 allele. Five patients with no intranuclear filaments were homozygous for the normal (GCG)6 allele. The pathologic expansion appeared to be stable with no variation among family members and between different tissues as blood and skeletal muscle in the same individual. CONCLUSIONS: These data 1) further confirm PABP2 gene analysis as a valuable tool in OPMD diagnosis; 2) indicate that PABP2 gene mutations are always present among Italian patients with morphologically proven OPMD, suggesting genetic homogeneity of the disease; and 3) strengthen the putative role of mutated PABP2 protein in filamentous inclusions accumulation.     

眼咽型肌营养不良一家系临床、电生理、病理及基因分析

目的 报道1个出现神经源性骨骼肌损害的眼咽型肌营养不良(OPMD)家系的临床、骨骼肌病理和基因改变特点.方法 先证者为60岁男性,50岁时出现双下肢近端无力,53岁出现吞咽困难和构音障碍,57岁出现双眼睑下垂和眼球突出.肌酸激酶轻度增加,四肢肌电图为神经源性损伤,周围神经传导速度下降20%～43%.家系3代中除先证者外尚有5例在45岁后出现吞咽困难,4～20年后出现眼睑下垂,其中3例有肢体无力.对先证者左肱二头肌做肌肉活体组织检查,标本进行组织学、酶组织化学以及免疫组织化学染色(以抗结蛋白和泛素蛋白抗体作为一抗)和超微病理检查.对先证者和家系中另外18人进行多腺苷酸结合蛋白(PABPN1)基因检查.结果 先证者肌纤维内出现镶边空泡伴泛素阳性沉积物和成组分布的小角状萎缩肌纤维,个别肌纤维出现再生改变伴随结蛋白沉积,可见细胞色素C氧化酶阴性肌纤维.电镜检查发现约3%的肌纤维核内存在栅栏样细丝包涵体.先证者和另外11名家系成员的PABPN1基因存在(GCG)9异常扩增.结论 杂合(GCG).异常扩增性OPMD可先出现咽喉肌无力,伴随脱髓鞘性神经病.我国患者也存在肌纤维核内包涵体.     

GCG repeats and phenotype in oculopharyngeal muscular dystrophy

Short GCG repeat expansions in the PABP2 gene were recently shown to cause oculopharyngeal muscular dystrophy (OPMD) in French-Canadian and Italian pedigrees. We diagnosed OPMD in 16 German patients by the detection of GCG repeat expansions, confirming genetic homogeneity. Myopathic and neurogenic changes were found in skeletal muscle biopsies. Age of onset and severity of disease were not correlated with the number of repeats.     

Two cases of oculopharyngeal muscular dystrophy (OPMD) with the rare PABPN1 c.35G>C; p.Gly12Ala point mutation

Oculopharyngeal muscular dystrophy is a neuromuscular disease usually presenting in the 5th or 6th decades of life with a dominant inheritance pattern. In almost all cases the cause of the disease is the expansion of a DNA repeat sequence containing GCG and GCA codons in exon 1 of the PABPN1 gene from 10 to between 12 and 17 repeats. However one case has been previously reported without the gene expansion but instead with a c.35G > C missense mutation converting a glycine codon to an alanine and resulting in a sequence of 13 contiguous alanine codons, thus mimicking the effect of the common expansion mutation. Here we report two further cases of OPMD caused by the c.35G > C point mutation. Clinical and pedigree data indicate the usual OPMD dominant inheritance pattern.