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DOK7 limb-girdle myasthenic syndrome mimicking congenital muscular dystrophy
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Neuromuscular Disorders 23 (2013) 36–42 www.elsevier.com/locate/nmd
DOK7 limb-girdle myasthenic syndrome mimicking congenital muscular dystrophy Ibrahim Mahjneh a,b,⇑, Hanns Lochmu¨ller c, Francesco Muntoni d, Angela Abicht e a Department of Neurology, University of Oulu, Oulu, Finland Department of Neurology, Pietarsaari Hospital, Pietarsaari, Finland c Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK d Dubowitz Neuromuscular Centre, Department of Neurosciences, UCL Institute of Child Health, London, UK e Friedrich-Baur-Institut, Ludwig Maximilians University, Munich, Germany b
Received 7 March 2012; received in revised form 23 May 2012; accepted 21 June 2012
Abstract Congenital myasthenic syndrome shows a wide clinical heterogeneity. However, the unusual pattern of muscle weakness and the presence of variable degree of muscle pathology, subtle electrophysiological abnormalities and lack of circadian variability of symptoms may complicate its recognition. We have previously reported a Palestinian family with suspected congenital muscular dystrophy and linkage to chromosome 4p16.3. As the DOK7 gene is located in this genetic interval, we considered it a potential candidate for this condition. Patients showed a homozygous DOK7 pathogenic mutation (c.957delC). We have re-examined six patients and found permanent limb-girdle weakness, but also episodic crises without clear precipitating factors. Following the revised diagnosis, patients were treated with salbutamol for 8 months with significant improvement in their muscle strength and function. This family needs to be reclassified as congenital myasthenic syndrome rather than congenital muscular dystrophy. Ó 2012 Elsevier B.V. All rights reserved. Keywords: Congenital muscular dystrophy; Congenital myasthenic syndromes; Limb-girdle myasthenic syndrome
1. Introduction Congenital myasthenic syndromes (CMS) are disorders of the neuromuscular junction resulting from defects in presynaptic, synaptic, or postsynaptic proteins. The protein encoded by DOK7 is essential for neuromuscular synaptogenesis due to its role in inducing autophosphorylation of the skeletal muscle receptor-like tyrosine kinase (MuSK), a key protein involved in postsynaptic differentiation [1]. Mutations in DOK7 result in small neuromuscular junctions but normal acetylcholine receptor and acetylcholinesterase function [2]. Electron microscopy studies of patients ⇑ Corresponding author. Address: Department of Neurology, Pietarsaari Hospital, PL111, 68601 Pietarsaari, Finland. Tel.: +358 40 7438361; fax: +358 6 7682510. E-mail address: ibrahim.mahjneh@mhso.fi (I. Mahjneh).
0960-8966/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nmd.2012.06.355
with DOK7 mutations show destruction and remodeling of end plates at neuromuscular junctions [3]. Clinically, a limb-girdle pattern of muscle involvement and absence of ophthalmoplegia make DOK7-related CMS distinguishable from other forms of CMS. Age at onset typically ranges from the birth to age 5 years [3] with onset in a minority of patients occurring beyond 5 years [4]. Congenital myasthenic syndromes show a wide clinical heterogeneity [5] however the unusual pattern of muscle weakness and the presence of variable degree of muscle pathology, together with the only subtle electrophysiological abnormalities and lack of circadian variability of symptoms may complicate its recognition. We have previously reported a Palestinian family with suspected congenital muscular dystrophy [6,7]. The family showed onset of symptoms at birth with muscle hypotonia and weakness. Muscle pathology in these patients showed
I. Mahjneh et al. / Neuromuscular Disorders 23 (2013) 36–42
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Table 1 (a–f) Patients’ functional abilities and muscle strength before and after the treatment with salbutamol. Motor Walking performances Before (a) V-10 (53 y)
(b) V-12 (51 y)
(c) IV-1 (44 y)
Mild waddling gait w/o assistance for 5 km
After
Climbing stairs
Rising from chair
Rising from floor
Upper limbs function
Before
Before
Before
Before
After
After
After
After
Muscle strength Before After
Slight Clinging Climbs waddling gait on knee or stairs for > 10 km railings, 20 upright, steps climbs w/o limits
Supports Normal on arms of chair
Two Normal hands on floor
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP HAB HAD HF HE KF KE APF ADF
4 4 4 2 4 2 3 4 4 3 3 4 4 4 4 4 3 3 4 4 4
5 5 5 2+ 5 2+ 4 4 5 4+ 5 5 5 5 5 4+ 4 4 5 5 5
Mild waddling Slight gait w/o waddling gait assistance for 2– for >7 km 4 km
Clinging on knee or railings, only 10–15 steps
Without assistance, can climb to the 5th floor
Supports Normal on arms of chair
Arises only with aid of object
Support with one hand on the floor
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP HAB HAD HF HE KF KE APF ADF
3+ 4 4 2 3 2 3 3 3+ 3 3 4 4 4 4 4 3 3 4 4 4
4+ 5 5 2+ 5 2+ 4 4 4 5 5 5 5 5 5 4+ 4 4 4 5 5
Mild wild gait, walks w/ o assistance, gait autonomy 2– 3 km
Manages to climb only a few steps with railings
w/o assistance 15 steps, after needs one side railing
Supports on arms of chair with great difficulty
Arises only with aid of object or person
Supports with one hand on knee
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP WF HAB HAD HF HE KF KE APF ADF
4 3 4 2 2 2 2 4 4 3 2 3 3 4 3 3 3 3 3 3 4 4
4+ 4 4 2+ 3+ 2+ 3 4 4+ 4+ 4 4 4 5 4 4 4+ 4 4 4 4+ 4+
Moderate waddling gait walking only with assistance from a person for 500 m
Rises with slight support on chair arms
(continued on next page)
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I. Mahjneh et al. / Neuromuscular Disorders 23 (2013) 36–42
Table 1 (continued) Motor Walking performances Before (d) IV-5 (38 y)
(e) IV-9 (43 y)
(f) IV-10 (41 y)
Climbing stairs
Rising from chair
Rising from floor
Upper limbs function
Before
After
Before
After
Before
After
Before
After
Severe waddling Walks w/o with one person assistance, for few meters moderate waddling for 50 m
Up steps on all fours few steps
Climbs clinging to railings with both hands 15 steps
Supports on a table
Rises with support on chair arms
Arises only with aid of person
Supports with both hands on floor and knees
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP WE HAB HAD HF HE KF KE APF ADF
4 3 3 2 2 2 2 3 2 3 2 3 3 4 3 3 3 3 3 3 3 4
4+ 4 4 2+ 2+ 2+ 2+ 3+ 3 4 4 4 4 5 4 4 4 4 3+ 3+ 4 4
Severe waddling Walks w/o with one person assistance, for few meters moderate waddling for 70 100 m
Up steps on all fours few steps
Climbs clinging to railings with both hands 15 steps
Support on one chair arm and knee
Rises with slight support on chair arms
Arises only with aid of person
Supports with one hand on knee
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP WF WE HAB HAD HF HE KF KE APF ADF
4 3 3 2 2 2 2 3 3 3 2 3 3 4 4 3 3 3 3 3 3 3 3
4+ 4+ 4+ 2+ 2+ 2+ 3 3 3+ 4 4 4 4 5 5 3+ 4 4 4 4 4 4 4
Moderate waddling for few meters
Up steps on all fours few steps
Climbs clinging to railings with both hands 25 steps
Support on both knees
Rises with slight support on knees
Arises only with aid of person
Supports with one hand on knee
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP WF WE HAB HAD HF HE KF KE APF ADF
3 3 3 2 2 2 2 3 3 3 2 3 3 4 3 3 3 3 3 3 3 3 3
4 4 4 2+ 2+ 2+ 2+ 3+ 4 4 3+ 4 4 5 4 4 4 4 4 4 4 4 4
After
Walks w/o assistance, mild waddling for > 100 m
Muscle strength Before After
Abbreviations: FM, face muscles; NE, neck extension; NF, neck flexion; SAB, shoulder abduction; SAD, shoulder adduction; SF, shoulder flexion; SE, shoulder extension; LAR, lateral arm rotation; MAR, medial arm rotation; EF, elbow flexion; EE, elbow extension; FAS, forearm supination; FAP, forearm pronation; WF, wrist flexion; WE, wrist extension; HAB, hip abduction; HAD, hip adduction; HF, hip flexion; HE, hip extension; KF, knee flexion; KE, knee extension; APF, Ankle plantar flexion; ADF, ankle dorsiflexion; w/o, without. Muscles not reported here showed normal strength before and after treatment.
I. Mahjneh et al. / Neuromuscular Disorders 23 (2013) 36–42
mild and non specific dystrophic features and EMG in all patients was myopathic [7]. Later, we established linkage to chromosome 4p16.3 [8], but could not identify mutations in any candidate gene. As the DOK7 gene is located in this genetic interval, more recently we considered it a potential candidate for this condition. All patients showed a homozygous DOK7 pathogenic mutation (c.957delC). This is a new mutation which causes limb-girdle myasthenic syndrome. Therefore, we believe it is important to report this data in order to clarify that this family does not have congenital muscular dystrophy (CMD) and the locus associated with this family should not be classified as CMD locus anymore. It also highlights the fact that patients with limb-girdle myasthenic syndrome could be easily misdiagnosed as congenital muscular dystrophy if fatigability is lacking or subtle. As in previously reported cases [9–11], we also documented in these patients improvement of muscle strength and function after the administration of the beta agonist salbutamol for 8 months. 2. Patients and methods One of the authors (IM) visited the family recently and re-examined six patients (4 m and 2f) aged 41–53 years (the patients previously have been referred as V-10, V-12, VI-1, VI-5, VI-9, VI-10 [6–8]). The patients are descending from related parents, with many intermarriages. They had generalized muscular weakness and hypotonia at birth without arthrogryposis. Hypotonia and weakness improved but the patients had delayed motor milestones, they were able to walk between 14–76 months. With growth, the pattern of muscle weakness and atrophy became clearer. Involvement was most marked in the proximal upper limb-girdle and trunk muscles, and mild to moderate in the proximal lower limb-girdle muscles. The distal muscle weakness of the limbs was milder. The small muscles of the hands and feet were spared. The symptoms in the lower limb-girdle muscles stabilized at different degrees of severity at ages varying from 7 to 26 years. However, slow progression of muscle weakness has been noticed on the upper limb-girdle muscles. Motor performances such as walking, climbing the stairs, rising from a chair and floor and upper limbs functions are affected with different degree of severity from mild to severe (Table 1). Episodic crises of severe weakness without clear precipitating factors have been reported. These crises can last 1–7 days, during which the patients are unable to get up from the chair or walk, and they usually require assistance of two persons. Only one patient (IV-9) reported that hot weather might sometimes aggravate his symptoms. This patient suffered of recurrent acute respiratory insufficiency for which he received BiPAP nocturnal ventilation (aged 42 years). There was no circadian aggravation of symptoms. They complained of inspiratory stridor during adult life. Breathing problems during excessive exercise were reported, which usually became more marked during
39
the crisis. Extraocular muscles were spared. They had swallowing or chewing difficulties during the severe weakness crisis. However, patient V-10 and V-12 showed permanent difficulties with chewing. 2.1. Physical examination The patients showed myopathic facies with mild bilateral ptosis and lip protrusion (Fig. 1B). The ptosis did not show fatigability. Facial muscle weakness was evident when smiling and blowing. Scoliosis was severe in two patients (IV-1 – Fig. 1A and IV-5) and mild in two patients (IV-9 – Fig. 2B and IV-10). Gait showed a waddle, slight in two patients (V-10 and V-12), and moderate in the others. During gait there was increased lordosis; gait acceleration was decreased, as well as cadence. Their stride length and step length became shorter. Three patients showed Gowers’ maneuver with different severity. The other three patients were unable to rise from the floor without external help. Four patients showed rigid spine. Muscle wasting was clearly seen in the upper limbgirdle and scapulae muscles (Fig. 1B). The muscle power testing showed marked worsening of muscle strength of the arm abductors in comparison with the last examination done 13 years ago (Table 1) [7]. They were unable to abduct their arms fully; active abduction was reduced to less than 30 degrees. Flexion of the elbow and the hand functions were less affected. Contractures were seen in patient IV-1, IV-5, IV-9 and IV-10. The contractures were present on the ankle dorsiflexion, knee extension, and hip extension as these patients were physically less active (Fig. 2B). The patients have never undergone physical therapy or other types of treatment. Serum CK levels were normal at this stage. Muscle biopsies from patient V-10 and IV-1 showed mild myopathic features [7]. IV-9 underwent a muscle biopsy in a medical centre in Israel, which showed normal findings. 2.1.1. Therapeutic intervention Following the CMS diagnosis, all patients received salbutamol 2 mg three times per day. The patients were examined before the initiation of the treatment and 8 months after it. Dramatic improvement in their motor performances and muscle power were noticed already after 1 week of treatment (Table 1) (Fig. 1). None of the patients experienced crisis during the treatment period. Two patients have had muscle cramps during the first week of treatment and one complained from chest pains and another of fine tremor. All patients showed marked improvement in respiratory function; patient IV-9 with marked respiratory problems had stopped the use of BiPAP because of improvement following medication. Patient V-10 complained of muscle pains at morning, which disappeared during treatment. The patients showed improvement on chewing and swallowing which was
40
I. Mahjneh et al. / Neuromuscular Disorders 23 (2013) 36–42
evident in patient V-10 and V-12, who gained 10 and 15 kg of weight respectively. Inspiratory stridor has completely disappeared under treatment. The significant physical improvement under salbutamol also led to improvement of the emotional status of the family. 2.2. Molecular genetics Venous blood samples were obtained from the index patient V-12. Genomic DNA was isolated using a blood and tissue culture DNA extraction kit according to the manufacturer’s recommendations (Wizard Genomic DNA Purification Kit, Promega, Mannheim, Germany). All studies were carried out with informed consent of the patients and were approved by the institutional ethics review board. Sequence analysis of the DOK7 gene revealed a homozygous mutation: an insertion of a C nucleotide in exon 7 leading to a frameshift (c.957del; p.Lys320SerfsX136). 3. Discussion Congenital muscular dystrophy is a clinically and genetically heterogeneous group of inherited muscle disorders. The cardinal hallmark is the onset of muscular symptoms – weakness and hypotonia – both at birth or within the first few months of life with a dystrophic pattern on muscle biopsy. Affected children may present with delay or arrest
of gross motor development together with joint and/or spinal rigidity. Muscle weakness may improve, worsen, or stabilize in the short term; however, with time progressive weakness and joint contractures, spinal deformities, and respiratory compromise may affect quality of life and life span. The diagnosis of CMD is based on the clinical findings, brain and muscle imaging, muscle biopsy histology, muscle and/or skin immunohistochemical staining, and molecular genetic testing. In some instances, such as the early phases of CMD secondary to mutations in SEPN1 or one of the three collagen 6 genes (COL6A1-3), muscle pathology can be subtle, with mostly mild and unspecific myopathic findings. Congenital myopathies are clearly different from CMD for the absence of necrosis and degenerative changes. The family presented here showed clinical features, which broadly fit the CMD diagnosis criteria. All patients showed floppy baby appearance at birth and delayed motor development. Muscle weakness was prominent on the limb-girdle musculature. The progression of the disease was characterized by plateau of clinical stabilization of symptoms. Muscle biopsy showed a mild and non specific dystrophic features and EMG showed a myopathic pattern [7]. The patients have not complained of circadian aggravation of muscle weakness [6,7]. During the hunting of the responsible gene of this disease, we previously mapped this family to a locus on chromosome 4p16.3 [8]. The locus found in our family was identical to the subsequently
Fig. 1. Clinical features and improvement during salbutamol treatment in patient V-12. The patient was unable to rise from the floor without support (A). He has a myopathic facies with mild bilateral ptosis and lip protrusion (B) and atrophy of the shoulder and scapulae muscles (C). Active abduction of the upper limbs was reduced to less than 30 degrees (B). After 8 months receiving salbutamol the patient was able to rise from the floor without difficulty (D). The upper limbs abduction and flexion were significantly improved (E).
I. Mahjneh et al. / Neuromuscular Disorders 23 (2013) 36–42
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Fig. 2. Scoliosis is observed with different severity: severe in (A) and mild in (B). Ankle, knee and pelvic contractures were also present (B).
described DOK7 locus, responsible for CMS [2,3]. Therefore, we tested our patients for the DOK7 gene mutation, and found a homozygous new pathogenic mutation which segregated with the phenotype. This finding prompted us to re-evaluate the family. As day-time- and exercise-dependent fatigability may be subtle or completely lacking in patients with limb-girdle CMS, they may be mistaken for congenital muscular dystrophy. In addition, CMS patients with DOK7 mutations may also show elevated CK levels and myopathic pathology on muscle biopsies. Not in all
patients with CMS a decremental response can be observed in a repetitive nerve stimulation, but if it is present, this strongly point towards a defect in neuromuscular transmission. However, this analysis was not carried out in our patients. What might have provided a clue clues towards a neuromuscular transmission defect, were unprovoked exacerbations of weakness and breathing difficulties over days or weeks, and spontaneous recovery from them. Improvement of muscle strength with ephedrine and salbutamol in patients with DOK7 mutation has been
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I. Mahjneh et al. / Neuromuscular Disorders 23 (2013) 36–42
reported [9–11]. This was confirmed also in our patients in whom significant improvement was demonstrated following salbutamol treatment, once more highlighting the importance to consider the diagnosis of a CMS as a treatable hereditary disorder. Acknowledgments FM is supported by the Great Ormond Street Children’s Charity. A.A. is supported by a grant from the Deutsche Forschungsgemeinschaft (Ab 130/2-1). References [1] Okada K, Inoue A, Okada M, et al. The muscle protein DOK-7 is essential for neuromuscular synaptogenesis. Science 2006;312:1802–5. [2] Beeson D, Higuchi O, Paalace J, et al. DOK-7 mutations underlie a neuromuscular junction synaptopathy. Science 2006;313:1975–8. [3] Selcen D, Milone M, Shen XM, et al. DOK-7 myasthenia: phenotypic and molecular genetic studies in 16 patients. Ann Neurol 2008;64:71–87.
[4] Mu¨ller JS, Herczegfalvi A, Vilchez JJ, et al. Phenotypical spectrum of DOK7 mutations in congenital myasthenic syndromes. Brain 2007;130:1497–506. [5] Mihaylova V, Mu¨ller JS, Vilchez JJ, et al. Clinical and molecular genetic findings in COLQ-mutant congenital myasthenic syndromes. Brain 2008;131:747–59. [6] Mahjneh I, Vannelli G, Bushby K, Marconi GP. A large inbred Palestinian family with two forms of muscular dystrophy. Neuromuscul Disord 1992;2:277–83. [7] Mahjneh I, Bushby K, Anderson L, et al. Merosin-positive congenital muscular dystrophy: a large inbred family. Neuropediatrics 1999;30:22–8. [8] Sellick GS, Longman C, Brockington M, et al. Localisation of merosin-positive congenital muscular dystrophy to chromosome 4q16.3. Hum Genet 2005;117:207–12. [9] Liewluck T, Selcen D, Engel AG. Beneficial effects of albuterol in congenital endplate acetylcholinesterase deficiency and DOK-7 myasthenia. Muscle Nerve 2011;44:789–94. [10] Lashley D, Palace J, Jayawant S, et al. Ephedrine treatment in congenital myasthenic syndrome due to mutations in DOK7. Neurology 2010;74:1517–23. [11] Schara U, Barisic N, Deschauer M, et al. Ephedrine therapy in eight patients with congenital myasthenic syndrome due to DOK7 mutations. Neuromuscul Disord 2009;19:828–32.
Neuromuscular Disorders 23 (2013) 36–42 www.elsevier.com/locate/nmd
DOK7 limb-girdle myasthenic syndrome mimicking congenital muscular dystrophy Ibrahim Mahjneh a,b,⇑, Hanns Lochmu¨ller c, Francesco Muntoni d, Angela Abicht e a Department of Neurology, University of Oulu, Oulu, Finland Department of Neurology, Pietarsaari Hospital, Pietarsaari, Finland c Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK d Dubowitz Neuromuscular Centre, Department of Neurosciences, UCL Institute of Child Health, London, UK e Friedrich-Baur-Institut, Ludwig Maximilians University, Munich, Germany b
Received 7 March 2012; received in revised form 23 May 2012; accepted 21 June 2012
Abstract Congenital myasthenic syndrome shows a wide clinical heterogeneity. However, the unusual pattern of muscle weakness and the presence of variable degree of muscle pathology, subtle electrophysiological abnormalities and lack of circadian variability of symptoms may complicate its recognition. We have previously reported a Palestinian family with suspected congenital muscular dystrophy and linkage to chromosome 4p16.3. As the DOK7 gene is located in this genetic interval, we considered it a potential candidate for this condition. Patients showed a homozygous DOK7 pathogenic mutation (c.957delC). We have re-examined six patients and found permanent limb-girdle weakness, but also episodic crises without clear precipitating factors. Following the revised diagnosis, patients were treated with salbutamol for 8 months with significant improvement in their muscle strength and function. This family needs to be reclassified as congenital myasthenic syndrome rather than congenital muscular dystrophy. Ó 2012 Elsevier B.V. All rights reserved. Keywords: Congenital muscular dystrophy; Congenital myasthenic syndromes; Limb-girdle myasthenic syndrome
1. Introduction Congenital myasthenic syndromes (CMS) are disorders of the neuromuscular junction resulting from defects in presynaptic, synaptic, or postsynaptic proteins. The protein encoded by DOK7 is essential for neuromuscular synaptogenesis due to its role in inducing autophosphorylation of the skeletal muscle receptor-like tyrosine kinase (MuSK), a key protein involved in postsynaptic differentiation [1]. Mutations in DOK7 result in small neuromuscular junctions but normal acetylcholine receptor and acetylcholinesterase function [2]. Electron microscopy studies of patients ⇑ Corresponding author. Address: Department of Neurology, Pietarsaari Hospital, PL111, 68601 Pietarsaari, Finland. Tel.: +358 40 7438361; fax: +358 6 7682510. E-mail address: ibrahim.mahjneh@mhso.fi (I. Mahjneh).
0960-8966/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nmd.2012.06.355
with DOK7 mutations show destruction and remodeling of end plates at neuromuscular junctions [3]. Clinically, a limb-girdle pattern of muscle involvement and absence of ophthalmoplegia make DOK7-related CMS distinguishable from other forms of CMS. Age at onset typically ranges from the birth to age 5 years [3] with onset in a minority of patients occurring beyond 5 years [4]. Congenital myasthenic syndromes show a wide clinical heterogeneity [5] however the unusual pattern of muscle weakness and the presence of variable degree of muscle pathology, together with the only subtle electrophysiological abnormalities and lack of circadian variability of symptoms may complicate its recognition. We have previously reported a Palestinian family with suspected congenital muscular dystrophy [6,7]. The family showed onset of symptoms at birth with muscle hypotonia and weakness. Muscle pathology in these patients showed
I. Mahjneh et al. / Neuromuscular Disorders 23 (2013) 36–42
37
Table 1 (a–f) Patients’ functional abilities and muscle strength before and after the treatment with salbutamol. Motor Walking performances Before (a) V-10 (53 y)
(b) V-12 (51 y)
(c) IV-1 (44 y)
Mild waddling gait w/o assistance for 5 km
After
Climbing stairs
Rising from chair
Rising from floor
Upper limbs function
Before
Before
Before
Before
After
After
After
After
Muscle strength Before After
Slight Clinging Climbs waddling gait on knee or stairs for > 10 km railings, 20 upright, steps climbs w/o limits
Supports Normal on arms of chair
Two Normal hands on floor
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP HAB HAD HF HE KF KE APF ADF
4 4 4 2 4 2 3 4 4 3 3 4 4 4 4 4 3 3 4 4 4
5 5 5 2+ 5 2+ 4 4 5 4+ 5 5 5 5 5 4+ 4 4 5 5 5
Mild waddling Slight gait w/o waddling gait assistance for 2– for >7 km 4 km
Clinging on knee or railings, only 10–15 steps
Without assistance, can climb to the 5th floor
Supports Normal on arms of chair
Arises only with aid of object
Support with one hand on the floor
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP HAB HAD HF HE KF KE APF ADF
3+ 4 4 2 3 2 3 3 3+ 3 3 4 4 4 4 4 3 3 4 4 4
4+ 5 5 2+ 5 2+ 4 4 4 5 5 5 5 5 5 4+ 4 4 4 5 5
Mild wild gait, walks w/ o assistance, gait autonomy 2– 3 km
Manages to climb only a few steps with railings
w/o assistance 15 steps, after needs one side railing
Supports on arms of chair with great difficulty
Arises only with aid of object or person
Supports with one hand on knee
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP WF HAB HAD HF HE KF KE APF ADF
4 3 4 2 2 2 2 4 4 3 2 3 3 4 3 3 3 3 3 3 4 4
4+ 4 4 2+ 3+ 2+ 3 4 4+ 4+ 4 4 4 5 4 4 4+ 4 4 4 4+ 4+
Moderate waddling gait walking only with assistance from a person for 500 m
Rises with slight support on chair arms
(continued on next page)
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I. Mahjneh et al. / Neuromuscular Disorders 23 (2013) 36–42
Table 1 (continued) Motor Walking performances Before (d) IV-5 (38 y)
(e) IV-9 (43 y)
(f) IV-10 (41 y)
Climbing stairs
Rising from chair
Rising from floor
Upper limbs function
Before
After
Before
After
Before
After
Before
After
Severe waddling Walks w/o with one person assistance, for few meters moderate waddling for 50 m
Up steps on all fours few steps
Climbs clinging to railings with both hands 15 steps
Supports on a table
Rises with support on chair arms
Arises only with aid of person
Supports with both hands on floor and knees
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP WE HAB HAD HF HE KF KE APF ADF
4 3 3 2 2 2 2 3 2 3 2 3 3 4 3 3 3 3 3 3 3 4
4+ 4 4 2+ 2+ 2+ 2+ 3+ 3 4 4 4 4 5 4 4 4 4 3+ 3+ 4 4
Severe waddling Walks w/o with one person assistance, for few meters moderate waddling for 70 100 m
Up steps on all fours few steps
Climbs clinging to railings with both hands 15 steps
Support on one chair arm and knee
Rises with slight support on chair arms
Arises only with aid of person
Supports with one hand on knee
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP WF WE HAB HAD HF HE KF KE APF ADF
4 3 3 2 2 2 2 3 3 3 2 3 3 4 4 3 3 3 3 3 3 3 3
4+ 4+ 4+ 2+ 2+ 2+ 3 3 3+ 4 4 4 4 5 5 3+ 4 4 4 4 4 4 4
Moderate waddling for few meters
Up steps on all fours few steps
Climbs clinging to railings with both hands 25 steps
Support on both knees
Rises with slight support on knees
Arises only with aid of person
Supports with one hand on knee
Unable to stretch arms to shoulder level
Can lift arms above the head only by flexing elbows
FM NE NF SAB SAD SF SE LAR MAR EF EE FAS FAP WF WE HAB HAD HF HE KF KE APF ADF
3 3 3 2 2 2 2 3 3 3 2 3 3 4 3 3 3 3 3 3 3 3 3
4 4 4 2+ 2+ 2+ 2+ 3+ 4 4 3+ 4 4 5 4 4 4 4 4 4 4 4 4
After
Walks w/o assistance, mild waddling for > 100 m
Muscle strength Before After
Abbreviations: FM, face muscles; NE, neck extension; NF, neck flexion; SAB, shoulder abduction; SAD, shoulder adduction; SF, shoulder flexion; SE, shoulder extension; LAR, lateral arm rotation; MAR, medial arm rotation; EF, elbow flexion; EE, elbow extension; FAS, forearm supination; FAP, forearm pronation; WF, wrist flexion; WE, wrist extension; HAB, hip abduction; HAD, hip adduction; HF, hip flexion; HE, hip extension; KF, knee flexion; KE, knee extension; APF, Ankle plantar flexion; ADF, ankle dorsiflexion; w/o, without. Muscles not reported here showed normal strength before and after treatment.
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mild and non specific dystrophic features and EMG in all patients was myopathic [7]. Later, we established linkage to chromosome 4p16.3 [8], but could not identify mutations in any candidate gene. As the DOK7 gene is located in this genetic interval, more recently we considered it a potential candidate for this condition. All patients showed a homozygous DOK7 pathogenic mutation (c.957delC). This is a new mutation which causes limb-girdle myasthenic syndrome. Therefore, we believe it is important to report this data in order to clarify that this family does not have congenital muscular dystrophy (CMD) and the locus associated with this family should not be classified as CMD locus anymore. It also highlights the fact that patients with limb-girdle myasthenic syndrome could be easily misdiagnosed as congenital muscular dystrophy if fatigability is lacking or subtle. As in previously reported cases [9–11], we also documented in these patients improvement of muscle strength and function after the administration of the beta agonist salbutamol for 8 months. 2. Patients and methods One of the authors (IM) visited the family recently and re-examined six patients (4 m and 2f) aged 41–53 years (the patients previously have been referred as V-10, V-12, VI-1, VI-5, VI-9, VI-10 [6–8]). The patients are descending from related parents, with many intermarriages. They had generalized muscular weakness and hypotonia at birth without arthrogryposis. Hypotonia and weakness improved but the patients had delayed motor milestones, they were able to walk between 14–76 months. With growth, the pattern of muscle weakness and atrophy became clearer. Involvement was most marked in the proximal upper limb-girdle and trunk muscles, and mild to moderate in the proximal lower limb-girdle muscles. The distal muscle weakness of the limbs was milder. The small muscles of the hands and feet were spared. The symptoms in the lower limb-girdle muscles stabilized at different degrees of severity at ages varying from 7 to 26 years. However, slow progression of muscle weakness has been noticed on the upper limb-girdle muscles. Motor performances such as walking, climbing the stairs, rising from a chair and floor and upper limbs functions are affected with different degree of severity from mild to severe (Table 1). Episodic crises of severe weakness without clear precipitating factors have been reported. These crises can last 1–7 days, during which the patients are unable to get up from the chair or walk, and they usually require assistance of two persons. Only one patient (IV-9) reported that hot weather might sometimes aggravate his symptoms. This patient suffered of recurrent acute respiratory insufficiency for which he received BiPAP nocturnal ventilation (aged 42 years). There was no circadian aggravation of symptoms. They complained of inspiratory stridor during adult life. Breathing problems during excessive exercise were reported, which usually became more marked during
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the crisis. Extraocular muscles were spared. They had swallowing or chewing difficulties during the severe weakness crisis. However, patient V-10 and V-12 showed permanent difficulties with chewing. 2.1. Physical examination The patients showed myopathic facies with mild bilateral ptosis and lip protrusion (Fig. 1B). The ptosis did not show fatigability. Facial muscle weakness was evident when smiling and blowing. Scoliosis was severe in two patients (IV-1 – Fig. 1A and IV-5) and mild in two patients (IV-9 – Fig. 2B and IV-10). Gait showed a waddle, slight in two patients (V-10 and V-12), and moderate in the others. During gait there was increased lordosis; gait acceleration was decreased, as well as cadence. Their stride length and step length became shorter. Three patients showed Gowers’ maneuver with different severity. The other three patients were unable to rise from the floor without external help. Four patients showed rigid spine. Muscle wasting was clearly seen in the upper limbgirdle and scapulae muscles (Fig. 1B). The muscle power testing showed marked worsening of muscle strength of the arm abductors in comparison with the last examination done 13 years ago (Table 1) [7]. They were unable to abduct their arms fully; active abduction was reduced to less than 30 degrees. Flexion of the elbow and the hand functions were less affected. Contractures were seen in patient IV-1, IV-5, IV-9 and IV-10. The contractures were present on the ankle dorsiflexion, knee extension, and hip extension as these patients were physically less active (Fig. 2B). The patients have never undergone physical therapy or other types of treatment. Serum CK levels were normal at this stage. Muscle biopsies from patient V-10 and IV-1 showed mild myopathic features [7]. IV-9 underwent a muscle biopsy in a medical centre in Israel, which showed normal findings. 2.1.1. Therapeutic intervention Following the CMS diagnosis, all patients received salbutamol 2 mg three times per day. The patients were examined before the initiation of the treatment and 8 months after it. Dramatic improvement in their motor performances and muscle power were noticed already after 1 week of treatment (Table 1) (Fig. 1). None of the patients experienced crisis during the treatment period. Two patients have had muscle cramps during the first week of treatment and one complained from chest pains and another of fine tremor. All patients showed marked improvement in respiratory function; patient IV-9 with marked respiratory problems had stopped the use of BiPAP because of improvement following medication. Patient V-10 complained of muscle pains at morning, which disappeared during treatment. The patients showed improvement on chewing and swallowing which was
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evident in patient V-10 and V-12, who gained 10 and 15 kg of weight respectively. Inspiratory stridor has completely disappeared under treatment. The significant physical improvement under salbutamol also led to improvement of the emotional status of the family. 2.2. Molecular genetics Venous blood samples were obtained from the index patient V-12. Genomic DNA was isolated using a blood and tissue culture DNA extraction kit according to the manufacturer’s recommendations (Wizard Genomic DNA Purification Kit, Promega, Mannheim, Germany). All studies were carried out with informed consent of the patients and were approved by the institutional ethics review board. Sequence analysis of the DOK7 gene revealed a homozygous mutation: an insertion of a C nucleotide in exon 7 leading to a frameshift (c.957del; p.Lys320SerfsX136). 3. Discussion Congenital muscular dystrophy is a clinically and genetically heterogeneous group of inherited muscle disorders. The cardinal hallmark is the onset of muscular symptoms – weakness and hypotonia – both at birth or within the first few months of life with a dystrophic pattern on muscle biopsy. Affected children may present with delay or arrest
of gross motor development together with joint and/or spinal rigidity. Muscle weakness may improve, worsen, or stabilize in the short term; however, with time progressive weakness and joint contractures, spinal deformities, and respiratory compromise may affect quality of life and life span. The diagnosis of CMD is based on the clinical findings, brain and muscle imaging, muscle biopsy histology, muscle and/or skin immunohistochemical staining, and molecular genetic testing. In some instances, such as the early phases of CMD secondary to mutations in SEPN1 or one of the three collagen 6 genes (COL6A1-3), muscle pathology can be subtle, with mostly mild and unspecific myopathic findings. Congenital myopathies are clearly different from CMD for the absence of necrosis and degenerative changes. The family presented here showed clinical features, which broadly fit the CMD diagnosis criteria. All patients showed floppy baby appearance at birth and delayed motor development. Muscle weakness was prominent on the limb-girdle musculature. The progression of the disease was characterized by plateau of clinical stabilization of symptoms. Muscle biopsy showed a mild and non specific dystrophic features and EMG showed a myopathic pattern [7]. The patients have not complained of circadian aggravation of muscle weakness [6,7]. During the hunting of the responsible gene of this disease, we previously mapped this family to a locus on chromosome 4p16.3 [8]. The locus found in our family was identical to the subsequently
Fig. 1. Clinical features and improvement during salbutamol treatment in patient V-12. The patient was unable to rise from the floor without support (A). He has a myopathic facies with mild bilateral ptosis and lip protrusion (B) and atrophy of the shoulder and scapulae muscles (C). Active abduction of the upper limbs was reduced to less than 30 degrees (B). After 8 months receiving salbutamol the patient was able to rise from the floor without difficulty (D). The upper limbs abduction and flexion were significantly improved (E).
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Fig. 2. Scoliosis is observed with different severity: severe in (A) and mild in (B). Ankle, knee and pelvic contractures were also present (B).
described DOK7 locus, responsible for CMS [2,3]. Therefore, we tested our patients for the DOK7 gene mutation, and found a homozygous new pathogenic mutation which segregated with the phenotype. This finding prompted us to re-evaluate the family. As day-time- and exercise-dependent fatigability may be subtle or completely lacking in patients with limb-girdle CMS, they may be mistaken for congenital muscular dystrophy. In addition, CMS patients with DOK7 mutations may also show elevated CK levels and myopathic pathology on muscle biopsies. Not in all
patients with CMS a decremental response can be observed in a repetitive nerve stimulation, but if it is present, this strongly point towards a defect in neuromuscular transmission. However, this analysis was not carried out in our patients. What might have provided a clue clues towards a neuromuscular transmission defect, were unprovoked exacerbations of weakness and breathing difficulties over days or weeks, and spontaneous recovery from them. Improvement of muscle strength with ephedrine and salbutamol in patients with DOK7 mutation has been
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reported [9–11]. This was confirmed also in our patients in whom significant improvement was demonstrated following salbutamol treatment, once more highlighting the importance to consider the diagnosis of a CMS as a treatable hereditary disorder. Acknowledgments FM is supported by the Great Ormond Street Children’s Charity. A.A. is supported by a grant from the Deutsche Forschungsgemeinschaft (Ab 130/2-1). References [1] Okada K, Inoue A, Okada M, et al. The muscle protein DOK-7 is essential for neuromuscular synaptogenesis. Science 2006;312:1802–5. [2] Beeson D, Higuchi O, Paalace J, et al. DOK-7 mutations underlie a neuromuscular junction synaptopathy. Science 2006;313:1975–8. [3] Selcen D, Milone M, Shen XM, et al. DOK-7 myasthenia: phenotypic and molecular genetic studies in 16 patients. Ann Neurol 2008;64:71–87.
[4] Mu¨ller JS, Herczegfalvi A, Vilchez JJ, et al. Phenotypical spectrum of DOK7 mutations in congenital myasthenic syndromes. Brain 2007;130:1497–506. [5] Mihaylova V, Mu¨ller JS, Vilchez JJ, et al. Clinical and molecular genetic findings in COLQ-mutant congenital myasthenic syndromes. Brain 2008;131:747–59. [6] Mahjneh I, Vannelli G, Bushby K, Marconi GP. A large inbred Palestinian family with two forms of muscular dystrophy. Neuromuscul Disord 1992;2:277–83. [7] Mahjneh I, Bushby K, Anderson L, et al. Merosin-positive congenital muscular dystrophy: a large inbred family. Neuropediatrics 1999;30:22–8. [8] Sellick GS, Longman C, Brockington M, et al. Localisation of merosin-positive congenital muscular dystrophy to chromosome 4q16.3. Hum Genet 2005;117:207–12. [9] Liewluck T, Selcen D, Engel AG. Beneficial effects of albuterol in congenital endplate acetylcholinesterase deficiency and DOK-7 myasthenia. Muscle Nerve 2011;44:789–94. [10] Lashley D, Palace J, Jayawant S, et al. Ephedrine treatment in congenital myasthenic syndrome due to mutations in DOK7. Neurology 2010;74:1517–23. [11] Schara U, Barisic N, Deschauer M, et al. Ephedrine therapy in eight patients with congenital myasthenic syndrome due to DOK7 mutations. Neuromuscul Disord 2009;19:828–32.