Novel TPM3 mutation in a family with cap myopathy and review of the literature

Novel TPM3 mutation in a family with cap myopathy and review of the literature

Available online at www.sciencedirect.com ScienceDirect Neuromuscular Disorders 24 (2014) 117–124 www.elsevier.com/locate/nmd Case report Novel TPM...

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Available online at www.sciencedirect.com

ScienceDirect Neuromuscular Disorders 24 (2014) 117–124 www.elsevier.com/locate/nmd

Case report

Novel TPM3 mutation in a family with cap myopathy and review of the literature T. Schreckenbach a,b, J.M. Schro¨der b, T. Voit c, A. Abicht d, E. Neuen-Jacob e, A. Roos b,f, S. Bulst d, C. Kuhl g, J.B. Schulz a,f, J. Weis b,f, K.G. Claeys a,b,f,⇑ a

Department of Neurology, University Hospital RWTH Aachen, Aachen, Germany Institute of Neuropathology, University Hospital RWTH Aachen, Aachen, Germany c Institut de Myologie, Universite´ Pierre et Marie Curie Paris, UM76, INSERM U 974, CNRS UMR 7215, Paris, France d Medizinisch Genetisches Zentrum Mu¨nchen, Mu¨nchen, Germany e Institute of Neuropathology, Heinrich-Heine-University Du¨sseldorf, Du¨sseldorf, Germany f JARA Translational Brain Medicine, Germany g Department of Radiology, University Hospital RWTH Aachen, Aachen, Germany b

Received 24 July 2013; received in revised form 8 October 2013; accepted 16 October 2013

Abstract Cap myopathy is a rare congenital myopathy characterized by the presence of caps within muscle fibres and caused by mutations in ACTA1, TPM2 or TPM3. Thus far, only three cases with TPM3-related cap myopathy have been described. Here, we report on the first autosomal dominant family with cap myopathy in three-generations, caused by a novel heterozygous mutation in the alpha-tropomyosin-slow-encoding gene (TPM3; exon 4; c.445C>A; p.Leu149Ile). The three patients experienced first symptoms of muscle weakness in childhood and followed a slowly progressive course. They presented generalized hypotrophy and mild muscle weakness, elongated face, high arched palate, micrognathia, scoliosis and respiratory involvement. Intrafamilial variability of skeletal deformities, respiratory involvement and mild cardiac abnormalities was noted. Muscle MRI revealed a recognizable pattern of fatty muscle infiltration and masseter muscle hypertrophy. Subsarcolemmal caps were present in 6–10% of the fibres and immunoreactive with anti-tropomyosin antibodies. We conclude that the MRI-pattern of muscle involvement and the presence of masseter muscle hypertrophy in cap myopathy may guide molecular genetic diagnosis towards a mutation in TPM3. Regular respiratory examinations are important, even if patients have no anamnestic clues. We compare our findings to all cases of cap myopathy with identified mutations (n = 11), thus far reported in the literature. Ó 2013 Elsevier B.V. All rights reserved. Keywords: Congenital myopathy; Alpha tropomyosin slow; Caps; Muscle fibre inclusions; Genotype–phenotype correlations; Whole-body muscle MRI

1. Introduction Cap myopathy is a rare congenital myopathy characterized by the presence of caps within muscle fibres, and was first described by Fidzianska et al. [1]. In parallel, ⇑ Corresponding author at: Klinik fu¨r Neurologie and Institut fu¨r Neuropathologie, Universita¨tsklinikum der RWTH Aachen, Pauwelsstrasse 30, 52074 Aachen, Germany. Tel.: +49 (0) 241 8036120; fax: +49 (0) 241 803389605. E-mail address: [email protected] (K.G. Claeys).

0960-8966/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nmd.2013.10.002

Schro¨der reported in his book a similar case, referring to it as ‘myopathy with subsarcolemmal-segmental myofibrillolysis’ [2]. Since the first descriptions only 16 other index cases have been reported [3–14]. Histopathologically, caps are peripherally located, sharply demarcated subsarcolemmal inclusions, which are purple-bluish or greenish on modified Gomori’s trichrome (mGT) and eosinophilic on hematoxylin and eosin (HE) stainings. They show dark-bluish reactivity for nicotinamide adenine dinucleotide-tetrazolium reductase (NADH-TR), while the myosin adenosine

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triphosphatase (ATPase) reaction is weak. Immunohistochemistry reveals reactivity of the caps for alpha-actinin, actin, troponin T, sarcomeric tropomyosin and desmin [3,5,6,8,10–15]. At the ultrastructural level, caps contain disorganized thin filaments and Z-disc material and are mainly devoid of thick filaments. Occasionally thickened Z-lines, appearing as rod-like structures are observed within the caps. The structure of adjacent sarcomeres is usually normal. In cap myopathy, the frequency of caps ranges from four to almost 100% of the muscle fibres [7–13] and seems to correlate with disease severity and patient’s age [3–5,10,12]. Clinical features of cap myopathy are onset in infancy or childhood, mainly proximal and axial muscle weakness, a long myopathic face with high arched palate, skeletal deformities, such as scoliosis, and respiratory problems. Severe cardiac involvement is not a common feature of cap myopathy and has been reported in only one patient, who presented a significantly reduced systolic function [8]. Creatine kinase (CK) level in serum is normal in most patients with cap myopathy. Electromyography (EMG) usually displays a myopathic pattern. Genetic analyses revealed thus far three causative genes of cap myopathy: ACTA1, encoding skeletal muscle alpha-actin [12], TPM2, encoding beta-tropomyosin [5–8,14] and TPM3, encoding alpha-tropomyosin slow [10,11,13]. In most patients, there is no family history and cap myopathy is caused by de novo dominant mutations. In 11 out of the 18 reported patients with cap myopathy, the genetic background has been clarified: one patient had a mutation in ACTA1 [12], seven patients harboured a TPM2 mutation [5–8,14] and in three patients a mutation in TPM3 was identified [10,11,13]. The proteins encoded by the ACTA1, TPM2 and TPM3 genes are components of the contractile apparatus. TPM2 and TPM3 are predominantly expressed in slow type 1 skeletal muscle fibres. Here, we report on a three-generation family with cap myopathy caused by a novel heterozygous mutation in TPM3. We highlight the clinical, histopathological, whole-body muscle MRI and molecular genetic findings and correlate our data to the literature. 2. Materials and methods 2.1. Clinical and paraclinical assessment We performed a general clinical and neurological examination in the index patient (II.2), her affected mother (I.1) and her affected son (III.1) (Fig. 1A). For strength testing, we used the Medical Research Council score (MRC). Paraclinical examinations included a blood analysis with serum CK, electro- and echocardiography, respiratory exams (including spirometry, whole-body plethysmography and blood gas analysis), electroneurography and -myography. A whole-body muscle MRI (1.5 Tesla, Philips, Intera, Best – The

D

A I.

1

2

3

II.

1

2*

III.

1*

2

E

B

C

Fig. 1. Pedigree and clinical presentation. (A) Pedigree of the family. Affected individuals are indicated in black, unaffected in white. The arrow points to the index patient. The asterisk indicates patients, in which the Leu149Ile TPM3 mutation has been identified. (B and C) Profile of the index patient and her son, showing an elongated face and micrognathia. (D and E) Posterior portraits of the index patient and her son showing a slim body constitution, generalized muscle hypotrophy and scapular winging. Scoliosis was prominent in the index patient (D). The patients signed an informed consent for publication of the photographs.

Netherlands) was performed in the index patient and her son. 2.2. Muscle biopsy An open muscle biopsy was performed in the index patient (II.2) (left quadriceps femoris muscle; 34 years) and her mother (I.1) (right quadriceps femoris muscle; 68 years) for diagnostic purposes after written informed consent. The tissue sample was divided for cryostat and paraffin-embedded and glutaraldehyde-fixed, epoxy-resin embedded sections, and prepared for further processing following routine protocols [16]. Immunohistochemical staining with an antibody directed against tropomyosin (TM311; mouse monoclonal; Sigma–Aldrich; 1:100) was performed on paraffin-embedded muscle tissue of patient I.1. For ultrastructural studies, we used a CM10 transmission electron microscope (Philips, Amsterdam, The Netherlands). 2.3. Molecular genetic analysis Blood samples for molecular genetic testing were obtained in patients I.2, II.2 and III.1, after written informed consent. The mother of the index patient had died prior to the current study, therefore genetic analysis was not possible. Direct sequencing of the coding regions

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and intron–exon boundaries of the TPM3 gene (OMIM 191030; NT_004487; NM_152263.2) was performed in the index patient (II.2), her father (I.2, unaffected) and her son (III.1, affected). Additionally, the coding exons of ACTA1 (exons 2–7) and TPM2 (exons 1–9, alternatively spliced exons 6 and 9, and intron 1) were sequenced in the index patient. The study was performed according to the Declaration of Helsinki and was approved by the Ethical committee of the University Hospital RWTH Aachen. 2.4. Patient history and results 2.4.1. Clinical presentation and examination The index patient (II.2; Fig. 1B and D) is a 45-year-old woman, who developed a mild proximal muscle weakness since early childhood. She never crawled and started to walk at the age of 2 years. She fell frequently and performed poorly at school sports. She suffered from mild progressive scoliosis since the age of 13 years (Fig. 1D). At the age of 45 years, she presented with a waddling gait and a mild proximal and distal lower limb weakness, resulting in problems to run and difficulties to climb the stairs. She walked unassisted without distance limitation. She had no myalgia, myoglobinuria, diplopia, dysarthria or dysphagia. Pulmonal infections or signs of respiratory insufficiency did not occur. The clinical neurological examination revealed generalized muscle hypotrophy and a body mass index (BMI) of 17.2. The index patient presented a long narrow face, high arched palate, discrete micrognathia (Fig. 1B), scoliosis and scapula alata (Fig. 1D). She did not present facial weakness, ophthalmoparesis, or ptosis. She could not walk on the heels, while toe walking was normal. The patient did not present a Gowers’ sign. Muscle strength was symmetrically decreased in the neck flexors (MRC 4/5), deltoid (4/5), biceps brachii (4/5), hamstrings (4/5), foot extensors (4/5) and foot supination and pronation (4/5) muscles. The index patient did not have foot deformities. Deep tendon reflexes were weak or absent. Touch and vibration sense were unremarkable. The patient’s son (III.1; Fig. 1C and E) had diffuse muscle hypotrophy and frequent falls since childhood. Pregnancy and delivery were normal, motor milestones were reached according to age. He experienced no problems at sports or during climbing stairs. At the age of 10 years, he developed a mild waddling gait. At the time of clinical examination (20 years), he did not complain of muscle weakness. He had no myalgia, myoglobinuria, diplopia, dysphagia, dysarthria, pulmonary infections or dyspnoe. Clinical examination revealed an elongated face, high arched palate and micrognathia (Fig. 1C). The patient presented generalized muscle hypotrophy (Fig. 1E) (BMI 15.3), and a mild waddling gait, but no difficulties to walk on heels or toes. He did not show a Gowers’ sign. Symmetrical weakness was present in neck flexors (4/5),

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deltoid muscles (4/5), scapulo-humeral muscles, resulting in scapular winging (Fig. 1E), and in feet extensors (4/5). Facial or extraocular weakness or ptosis was not present. The patient had no prominent scoliosis, but presented with bilateral pes planovalgus. Deep tendon reflexes were absent. Perception of vibration and touch was normal. The mother (I.1) of the index patient showed a waddling gait and difficulties to climb the stairs since childhood. The first clinical investigation was performed at the age of 68 years, when she suffered from acute respiratory failure in association with a pulmonary infection. At that time, assisted walking distance was reduced to 100 m. She presented a thoracic scoliosis, generalized muscle hypotrophy and weakness, most pronounced in the neck flexors (2/5), deltoid muscles (2/5) and feet extensors (3/5). Cranial nerves were unaffected, she particularly had no ophthalmoplegia or ptosis. Deep tendon reflexes were absent. Sensibility was normal. She died at the age of 68 years due to respiratory insufficiency, most probably related to the cap myopathy. 2.4.2. Paraclinical examinations Serum CK levels were examined in patients II.2 and III.1 and were normal. Echocardiography showed a mild mitral valve insufficiency in the index patient (II.2), whereas a slight tricuspid valve insufficiency, mild anterior mitral leaflet prolapse and mild restricted right heart function were revealed in her son (patient III.1), and minor left ventricular hypertrophy in her mother (patient I.1). Electrocardiography showed no significant abnormalities except for a right axis deviation in the index patient and her son. Respiratory exams revealed pronounced restrictive ventilation disturbances in patient I.1 (further data were not available) and restrictive lung disease in patient III.1 (vital capacity 62% of predicted value and mild hypoxemic global insufficiency at blood gas analysis). Examination of the index patient did not reveal respiratory abnormalities. Nerve conduction studies were normal in the three patients. Electromyography (tibialis anterior muscle) revealed a myopathic pattern in all patients and additional chronic neurogenic changes in the index patient’s mother (I.1). 2.4.3. Muscle imaging Whole-body muscle MRI was performed in the index patient (II.2) and her son (III.1) (Fig. 2). In the index patient, MRI revealed symmetrical fatty infiltration in paraspinal muscles (Fig. 2C), gluteus maximus and minimus (Fig. 2E), semimembranosus and biceps femoris muscles (Fig. 2G), and less pronounced in soleus and tibial anterior muscles (Fig. 2I). In patient III.1, symmetrical slight fatty infiltration was present in gluteus minimus (Fig. 2F) and soleus muscles (Fig. 2J). Interestingly, bilateral masseter muscle hypertrophy was observed in both patients (Fig. 2A and B). Shoulder girdle muscles and upper limb muscles were relatively spared.

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Fig. 2. Whole-body muscle MRI findings. MRI images of the index patient (II.2, left column) and her son (III.1, right column) at the level of the face (A and B), lumbar spinal column (C and D), pelvic girdle (E and F), thighs (G and H) and calves (I and J). (A and B) Symmetric hypertrophy of masseter muscles (arrow head). (C) Pronounced fatty infiltration of paraspinal muscles (arrow) and signs of scoliosis in the index patient, which are both absent in her son (D). (E and F) Fatty infiltration in gluteus maximus (arrow) and gluteus minimus muscles (arrow head) in patient II.2 (E), whereas in patient III.1 slight fatty infiltration is observed only in gluteus minimus muscle (arrow head) (F). (G) Affection of the posterior thigh compartment, particularly semimembranosus (arrow) and biceps femoris (arrow head) muscles, whereas semitendinosus muscles and the quadriceps femoris, adductor magnus and longus, gracilis and sartorius muscles are relatively preserved in the index patient. The proximal lower limb abnormalities were not found in patient III.1 (H). (I and J) The soleus muscle shows fatty infiltration in both patients (arrow). The tibial anterior muscle (arrow head) is additionally affected in the index patient (I), but not in her son (J). In both patients, medial and lateral gastrocnemius muscles and peroneus muscles are relatively spared.

2.4.4. Muscle biopsy The muscle biopsy of the index patient (left quadriceps femoris muscle; 34 years; performed 11 years prior to her first presentation at our neurological department) showed cap-shaped, bluish subsarcolemmal inclusions in 6% of the fibres on mGT (Fig. 3A), that were slightly eosinophilic on HE (Fig. 3B). The caps comprised up to 50% of the muscle fibre at transverse sections. Myosin ATPase reactivity was reduced in the cap areas (Fig. 3C and D). The cap structures were darkly stained on NADH-TR (Fig. 3E) and were not detectable on periodic

acid-Schiff (PAS) staining. The myosin ATPase stains revealed type 1 fibre predominance. Numerous atrophic fibres and nuclear bags were observed. The endomysial connective tissue was not increased. Rare myophagic reactions in muscle fibres were present, while inflammatory infiltrates were absent. The biopsy findings in patient I.1 (right quadriceps femoris muscle; 68 years) were overall similar with the histopathological findings in the index patient (Fig. 3G). Caps were present in 10% of the muscle fibres and were also exclusively seen in subsarcolemmal position,

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Fig. 3. Muscle biopsy light and electron microscopic findings. (A–E) Serial sections of the index patient’s biopsy. The cap structures (arrows) are revealed as dark-green to bluish well-demarcated inclusions on mGT sections (A), and slightly visible eosinophilic areas on HE (B). ATPase reactions show type 1 fibre predominance (pH 4.2) (C and D) and pale appearance of the caps. On NADH-TR (E), caps are stained intensively blue (arrow). (F) Electron microscopic image showing a cap that is located beneath the sarcolemma and is well demarcated from adjacent structurally normal sarcomeres. The cap contains thin filaments and Z-disc material (magnification 3600). (G and H) Biopsy findings in the index patient’s mother (patient I.1). (G) Multiple caps are seen in subsarcolemmal position on mGT stains (arrows). (H) The caps are immunoreactive for antibodies directed against tropomyosin (arrow). Magnification bar of the light microscopic pictures corresponds to 50 lm.

comprising up to 40% of the muscle fibre. The caps were immunoreactive for antibodies directed against tropomyosin (Fig. 3H). We did not additionally find cytoplasmic or intranuclear rods, actin filament aggregates or cores in either of the biopsies. At electron microscopic level (EM) the inclusions contained disorganized, fragmented thin myofibrils, with

actin- and few thick filaments as well as Z-disc material (Fig. 3F). The structure of adjacent myofibrils was normal. 2.4.5. Molecular genetic analyses We identified a heterozygous, previously not described missense mutation (exon 4; c.445C>A; p.Leu149Ile) in the TPM3 gene (OMIM 191030; NT_004487;

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NM_152263.2) in the index patient and her affected son. This nucleotid change was not present in the index patient’s clinically unaffected father. ACTA1 was additionally sequenced in the index patient and showed no abnormalities. In TPM2, we found two previously described, non-pathogenic intronic polymorphisms in intron 5 and 8 of the TPM2 gene (c.564-19dupC in intron 5; c.773-3dupC in intron 8) (http://www.dmd.nl).

muscle MRI revealed a recognizable pattern of muscle involvement and bilateral masseter muscle hypertrophy. The majority of previously described patients with cap myopathy, associated with mutations in ACTA1, TPM2 or TPM3, as well as the currently reported family presented with a similar clinical phenotype (reviewed in Table 1): onset in infancy or childhood, delayed motor milestones, diffuse limb and axial muscle weakness, generalized muscle hypotrophy, scoliosis, elongated face, high arched palate and reduced vital capacity. Some patients rely on ventilatory support. Mild, unspecific cardiac abnormalities are described in a minority of cases (e.g. valve insufficiency, aortic dilatation or mildly reduced cardiac function). In one case with TPM2 mutation, cardiac involvement was severe (Table 1; [8]). Since subjective respiratory (and cardiac) symptoms may be absent, we emphasize the importance of regular respiratory and cardiac examinations in patients with cap myopathy. Facial weakness, ophthalmoparesis, ptosis, dysphagia and limb contractures are less common features of cap myopathy and have thus far only been reported in patients with TPM2 mutations (Table 1).

3. Discussion In this study, we report on the first family with an autosomal dominant cap myopathy in three generations, caused by a novel missense mutation in TPM3 (exon 4; c.445C>A; p.Leu149Ile), the fourth case thus far described in the literature. The affected family members presented a typical clinical phenotype with childhood onset and a stable to slowly progressive course. Interestingly, intrafamilial variability concerning the presence of skeletal deformities, respiratory involvement and mild cardiac abnormalities was present. Whole-body

Table 1 Clinical, paraclinical and biopsy findings in patients with cap myopathy and identified mutation, reported in the literature and in the current study. Reference

Gene Mutation Age at onset DMM AAE (years) Weakness

Prox. UL Dist.UL Prox. LL Dist. LL Axial Facial OP Ptosis Dysphagia

Hypotrophy Limb contractures

Scoliosis Elongated face High-arched palate Respiratory abnormalities Cardiac abnormalities

% of fibres with caps

This report

[13]

[10]

[11]

[14]

[8]

[7]

[7]

[7]

[6]

[5]

[12]

TPM3 L149I Child + 20; 45; 68 + + + + +     + 

TPM3 R168C Infant  20

TPM3 R168H Infant + 42

TPM3 R168C Child + 38

TPM2 E139del Infant + 14

TPM2 K49del Infant  42

TPM2 G52dup Infant + 6

TPM2 N202K Prenat. + 8

ACTA1 M49N Prenat. + 5

  + +  na na  na + na

+  +  na na na na na + na

+ + + + + +   na + Ankles

+  +    na na na + Hips

+ + + + + + + + + + +

+  + + + + na + na + na

+ + + + + na na na + + na

+ + + VC#

+ + + VC#, NIV AD

+ + + VC#

+ + + IV



+ + + VC#, NIV 

na na + IV



+ na na VC#, IV 

na na + NIV



+ + + VC#, HV EF#, VI, AD

+ na na VC#



+ + + VC#, IV 

+ + + + + +   na + Hips, finger flexors, rigid spine  na na 

TPM2 E41K Infant + 35; 66 + + + + + + na + + na na

TPM2 E139del Birth + 36

+ + + + + na na na na na na

TPM2 E138del Child  14; 15; 47 +   + + na na na na na Rigid spine



AH, LVDD"

25

10–15

20–25

na

4

15

na

na

na

na

100

RH#, VI, LV" 6; 10

DMM, delayed motor milestones; AAE, age at latest examination; Prox., proximal; Dist., distal; UL, upper limbs; LL, lower limbs; OP ophthalmoparesis; Prenat., prenatal; +, present; , absent; na, not available; VC#, decreased vital capacity; NIV, non-invasive ventilation (includes CPAP and BiPAP); IV, invasive ventilation; HV, central hypoventilation; RH#, mild restricted right cardiac function; VI, mild valve insufficiencies; LV", minor left ventricular hypertrophy; AD, borderline aortic dilatation; EF#, reduction of ejection fraction; AH, arterial hypertension; LVDD", mildly increased left ventricular dimensions.

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Only three sporadic cases with TPM3-associated cap myopathy with de novo mutations have thus far been described (Table 1). Here, we report the first autosomal dominant family with TPM3-associated cap myopathy. Mutations in the TPM3 gene can also cause other congenital myopathies, particularly nemaline myopathy (NEM) and congenital fibre type disproportion (CFTD). Most clinical features in our family with cap myopathy are in accordance with findings in NEM and CFTD: stable or slow progressive courses, proximal, distal and axial muscle weakness, scoliosis, high arched palate and respiratory involvement. In contrast, patients with TPM3 nemaline myopathy often have a marked myopathic face [17]. Weakness of neck flexion and ankle dorsiflexion, which were prominent in our family, are also found in CFTD caused by TPM3 mutations [18]. In contrast to NEM, severe cases with death in infancy are rare in cap myopathy. Only one case of severe cap myopathy, associated with death at the fifth year of life has been reported. This patient carried an ACTA1 mutation [12]. In one case of TPM3-associated cap myopathy [10], muscle computer tomography showed fatty infiltration of paravertebral, gluteal, biceps femoris, soleus and feet extensor muscles. However, masseter muscles were not examined. Three other reports of muscle MRI in patients with cap myopathy and TPM2 mutations describe involvement of gluteus maximus, sartorius and anterolateral leg compartment muscles [14], or fatty infiltration of paravertebral, gluteus maximus and hamstring muscles with sparing of rectus femoris, gracilis and sartorius muscles [5], or masticator, paraspinal, biceps femoris, soleus and tibiales muscle involvement [19]. Therefore, common muscle MRI findings in patients with cap myopathy caused by TPM2 and TPM3 mutations may be paraspinal, gluteal, hamstrings (especially biceps femoris), soleus and tibialis anterior muscles involvement with relative sparing of rectus femoris and gastrocnemius muscles. This pattern of muscle involvement is congruent to that seen in our study. Interestingly, we additionally found bilateral masseter muscle hypertrophy, which has not been described previously. In one TPM2-associated patient with cap myopathy, fatty infiltration (without hypertrophy) in masseter, temporal and pterygoidei muscles was reported [19]. In other TPM3 related myopathies (NEM, CFTD), muscle MRI either reveals involvement of paravertebral, abdominal and gluteal muscles [20] or shows unspecific increase of interstitial or fatty tissue [21]. Furthermore, the pattern of MRI muscle involvement in our family did not correspond to the previously reviewed patterns in distinct congenital myopathies caused by mutations in other genes, such as RYR1, SEPN1, DNM2, MTM1, NEB, MYH7, ACTA1 or TPM2 (reviewed in [22]). Therefore, the pattern of muscle involvement combined with masseter muscle hypertrophy on muscle MRI might help to orient the genetic diagnosis in cap myopathy towards a TPM3 mutation.

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Muscle biopsy in our patients revealed typical caps with light and electron microscopic characteristics and immunohistochemical features corresponding to previous reports [1–15]. The number of cap structures seems to correlate with disease severity and age [3–5,10,12] (Table 1). In our study, we found a discrete difference concerning the number of fibres with caps in the biopsies of the two patients. In the index patient, caps were present in 6% of the fibres (age at biopsy was 34 years), while her mother showed 10% of cap-containing fibres (biopsy at 68 years). Whether this is an effect of age and disease severity or a selection bias remains unclear, though both biopsies were performed in the quadriceps muscle. Several reports describe the clinical, genetic and histopathological overlap between cap myopathy, NEM, CFTD and core myopathy [4,6,8–11,14,18,21,23–25]. In some cases, even the same mutation causes distinct histopathologies in different patients, including cap myopathy, CFTD and NEM [10,11,13,18,21,23–25], occasionally even in the same family [4,6]. These findings are confirmed by occasional concomitant electron microscopic findings of rod-like structures in the cap formations [10] and the progression of typical CFTD pattern to cap structures in a twice biopsied patient [10]. Missense mutations at position p.Leu149 have thus far not been reported in TPM3. Several facts provide evidence that this mutation causes cap myopathy in the currently reported family. The mutation was found in the index patient and her affected son, while the unaffected father of the index patient did not carry the mutation. Thus, the mutation segregated with the disease. Furthermore, the mutation was not found in relevant databases and the ACTA1 and TPM2 genes, which are the two other known causative genes of cap myopathy, were additionally sequenced and revealed no pathogenetic variants. In addition, the caps showed immunoreactivity for antibodies directed against tropomyosin. To our knowledge, this is the first report of a mutation at amino acid position 149 of TPM3 (exon 4). TPM3 mutations causing cap myopathy are described in exons 4 and 5 of the TPM3 gene [10,11,13]. Interestingly, mutations in TPM3 causing nemaline myopathy and CFTD are reported all over the TPM3 gene, including exons 4 and 5. The exon 4 is present in TPM1, TPM2 and TPM3 with minor variations in amino acid sequence (http://www.dmd.nl). Cap myopathy associated mutations in ACTA1, TPM2 and TPM3 may present as missense mutations, small duplications or deletions (Table 1). In this family, the p.Leu149 missense mutation causes the exchange of the highly conserved amino acid leucin. Bioinformatic analysis using PolyPhen-2 (http://genetics.bwh.harvard.edu/ggi/ pph2; [26]) predicts probably damaging of the mutation with a score of 0.991 (sensitivity: 0.72; specificity: 0.96). The mutation may influence the strictly organized alpha-helical coiled coil protein structure and interaction with other proteins (e.g. F-actin), resulting in the described clinico-histopathological phenotype. Up to now, the

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variety of genes, different kinds of mutations and amino acid exchanges, all resulting in the histopathological cap myopathy-phenotype, as well as the overlap to other myopathies is not sufficiently understood. Further studies are needed to understand the underlying pathomechanisms and currently unknown modifying factors. 4. Conclusions Although the clinical presentation is not specific for cap myopathy but rather typical for the heterogeneous group of overlapping congenital myopathies, clinicians should think of cap myopathy in patients with childhood onset, mild progressive generalized hypotrophy and mild muscle weakness, associated with an elongated face, high arched palate and scoliosis. The diagnosis is suspected based on clinical features but a muscle biopsy is necessary to confirm cap myopathy. The MRI pattern of muscle involvement and the presence of masseter muscle hypertrophy may further guide molecular genetic diagnosis. Regular respiratory and cardiac examinations are important, even when patients have no anamnestic clues for respiratory or heart involvement. Acknowledgements We thank the patients and their family for participating in our study. We are grateful to the technical and administrative personnel of the Department of Neurology, the Institute of Neuropathology and the Department of Radiology of the University Hospital Aachen for their support. References [1] Fidzianska A, Badurska B, Ryniewicz B, Dembek I. “Cap disease”: new congenital myopathy. Neurology 1981;31(9):1113–20. [2] Schro¨der JM. Pathologie der muskulatur. Berlin Heidelberg, New York: Springer; 1982, p. 262–4. [3] Fidzian´ska A. “Cap disease”-a failure in the correct muscle fibre formation. J Neurol Sci 2002;201(1–2):27–31. [4] Cuisset JM, Maurage CA, Pellissier JF, et al. ‘Cap myopathy’: case report of a family. Neuromuscul Disord 2006;16(4):277–81. [5] Lehtokari VL, Ceuterick-de Groote C, de Jonghe P, et al. Cap disease caused by heterozygous deletion of the beta-tropomyosin gene TPM2. Neuromuscul Disord 2007;17(6):433–42. [6] Tajsharghi H, Ohlsson M, Lindberg C, Oldfors A. Congenital myopathy with nemaline rods and cap structures caused by a mutation in the beta-tropomyosin gene (TPM2). Arch Neurol 2007;64(9):1334–8. [7] Ohlsson M, Quijano-Roy S, Darin N, et al. New morphologic and genetic findings in cap disease associated with beta-tropomyosin (TPM2) mutations. Neurology 2008;71(23):1896–901.

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