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Monomelic amyotrophy associated with the 7472insC mutation in the mtDNA tRNASer(UCN) gene
Neuromuscular Disorders 14 (2004) 723–726 www.elsevier.com/locate/nmd
Case report
Monomelic amyotrophy associated with the 7472insC mutation in the mtDNA tRNASer(UCN) gene Vincenza Fetonia, Egill Briemb, Franco Carrarab, Marina Morac, Massimo Zevianib,1,* b
a Unit of Neurology, Public Health Hospital, Melegnano (Milan), Italy Unit of Molecular Neurogenetics—Pierfranco and Luisa Mariani Center for the Study of Children’s Mitochondrial Disorders, National Neurological Institute ‘Carlo Besta’, via Temolo 4, Milan 20133, Italy c Unit of Neuromuscular Disorders, National Neurological Institute ‘Carlo Besta’, via Temolo 4, Milan 20133, Italy
Received 8 April 2004; received in revised form 5 July 2004; accepted 8 July 2004
Abstract We describe a 49-year-old male patient who experienced progressive amyotrophy with no sensorial abnormality in the left arm since 45 years of age. The neuromuscular syndrome was identical to that known as Hirayama disease, a rare form of focal lower motor neuron disease affecting the C7–C8–T1 metamers of the spinal cord. Asymmetric neurosensorial hearing loss was present since age 35 in the patient, and was also documented in an elder sister and in the mother. A muscle biopsy showed cytochrome c oxidase (COX) negative fibers but no ragged-red fibers, and mild reduction of COX was confirmed biochemically. The patient was found to have high levels of a known pathogenic mutation of mtDNA, the 7472insC in the gene encoding the tRNASer(UCN). Investigation on several family members showed a correlation between mutation load and clinical severity. This is the second report documenting the association of lower motor neurone involvement with a specific mtDNA. q 2004 Elsevier B.V. All rights reserved.
1. Introduction Monomelic amyotrophy (Hirayama disease, MIM %602440) is a rare form of motor neuron disease (MND) affecting a single, usually upper, limb [1]. Focal, monolateral lower motor neuron degeneration is believed to occur in the C7–T1 metamers. ‘Oblique amyotrophy’ is a descriptive term to emphasize the sparing of the brachioradialis muscle in the forearm of these patients. After a subacute onset, the course of the disease is stable or slowly progressive. Late involvement of the shoulder or contralateral limb has rarely been reported. The etiology of the syndrome, which is more frequent in young adult males, is unknown. Chronic compression of the cervical spinal cord by a thickened and inelastic dura mater has been hypothesized as the pathogenetic mechanism in a few MRI-documented cases. Several patients originated from * Corresponding author. Tel.: C39-02-2394630; fax: C39-02-2394619. E-mail addresses: [email protected] (M. Zeviani), [email protected] (M. Zeviani). 1 URL: www.mitopedia.org. 0960-8966/$ - see front matter q 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nmd.2004.07.002
Eastern India, which suggests that specific environmental factors, ethnic background, or cultural and behavioral habits may influence the susceptibility to disease. A genetic cause is also suggested by the observation of rare familial cases [2,3]. We report on an Italian patient with adult-onset monomelic amyotrophy associated with a known pathogenic mutation of mtDNA, the 7472insC in the gene encoding the tRNASer(UCN).
2. Case report The proband, a 49-year-old man, is the third of five siblings born from non-consanguineous parents (Fig. 1). His father, deceased at 78 years, suffered from non-insulin dependent diabetes mellitus (NIDDM); the mother, now 88, and an elder sister, now 51, are both suffering of moderate, bilateral neurosensory hearing loss. At age 45, he started complaining of rapidly progressive weakness and wasting of the left upper limb, accompanied
724
V. Fetoni et al. / Neuromuscular Disorders 14 (2004) 723–726
Fig. 2. Histoenzymatic stainings on skeletal muscle consecutive sections. Left panel, succinate dehydrogenase (SDH). Right panel, cytochrome c oxidase (COX). The asterisks indicate COX-negative fibres. !200.
Fig. 1. Pedigree. A black symbol indicates the proband. Half-blackened symbols indicate subjects with hearing loss. A shaded symbol indicates a subject with mild gait instability and a ‘restless-leg like’ syndrome (see text). The percentage of mutation loads in muscle (M) or lymphocyte (L) mtDNA are also indicated. A query point indicates subjects that were not analyzed.
by cramps and tremor, with no sensorial abnormality. During the following 4 years, the muscle symptoms have remained relatively stable. Before the onset of the neuromuscular problems, the only reported complaint was a non-syndromic bilateral neurosensorial hearing loss, more severe in the left ear, which was documented by audiometric examination at age 39. At age 48 he developed NIDDM, controlled by low-glucose diet. When first examined at age 45, the patient had a severe monomelic amyotrophy affecting the C7–C8–T1 left metamers with fasciculations and coarse tremor of the fingers. Severe weakness and hypotrophy involved the interosseous muscles of the hand, the dorsal and flexor muscles of the forearm, with sparing of the brachioradialis, and the extensor muscles of the arm, including the triceps brachii, while the biceps brachii was spared. Apart from the absence of the left tricipital reflex, the tendon reflexes were brisk in all four limbs. The neuromuscular symptoms have hitherto remained stable although occasional fasciculations were recently observed in the contralateral arm. An EMG examination at age 46 showed a neurogenic pattern in the left C6–C7–C8 metamers, characterized by signs of active denervation with spontaneous electric activity (fasciculation potentials), and high-amplitude and prolonged motor potentials during voluntary contraction of the flexor muscles of the forearm and extensor muscles of the arm. The conduction velocity and composite motor amplitude potentials (CMAP) were both normal in the same districts, which excludes the presence of both demyelination and conduction blocks. Brain and cervical MRI were normal, with no sign of compression of the cervical spinal cord. Evoked Motor Potentials, the EEG and the CSF examination were also normal, including the search for oligoclonal bands. The following laboratory tests were normal as well: serum CK, lactic acid, parathyroid hormone, T3, T4, TSH hormones, alpha-fetoprotein, carcino-embryonal antigen, prostatic serum antigen,
and electrolytes. Search for anti-borrelia, anti-GM1, and autoantibodies was negative. A second EMG, performed at age 48, confirmed the neurogenic pattern on the left side, involving the C7–C8–T1 metamers. However, the presence of low-voltage potentials in the C5–C6 metamers on both sides, corresponding to the deltoid muscles, suggested a concomitant, myogenic abnormality, and prompted us to perform a muscle biopsy in the left quadriceps. Morphological analysis of skeletal muscle and biochemical assays of the individual respiratory complexes on muscle homogenate were carried out as described [4,5]. In addition to signs of denervation, such as variation in the fiber size and a tendency to type grouping, the light microscopy examination disclosed the presence of a few cytochrome c oxidase negative fibers (Fig. 2). Some fibers were also hyperreactive to succinate dehydrogenase. The latter finding demonstrates that, in spite of the absence of obvious ragged-red fibers at the modified trichrome Gomori staining, some proliferation of mitochondria occurred in the skeletal muscle of the patient, as typically seen in mitochondrial myopathies. Biochemical analysis of the respiratory chain complexes, performed on muscle homogenate, revealed a mild reduction of cytochrome c oxidase, while the other enzyme activities were within the control ranges (Table 1). Nucleotide sequence analysis was then performed on eleven overlapping PCR fragments encompassing the entire mtDNA molecule [6]. The data were compared to the revised Cambridge sequence of human mtDNA [7]. In addition to a few homoplasmic changes that were already reported as non-pathogenic polymorphisms (not shown), we identified a heteroplasmic Table 1 Respiratory chain activities in muscle homogenate
Complex I/CS Complex II/CS Complex III/CS Complex IV/CS Complex V/CS Succinate dehydrogenase Citrate synthase
Patient
Control range
21.3 31.3 71.7 64 145 21.3 105
15–25 15–28 70–150 80–180 75–180 10–20 80–210
Specific activities are expressed as nmoles/min/mg protein.
V. Fetoni et al. / Neuromuscular Disorders 14 (2004) 723–726
mutation, consisting in the insertion of a cytosine at nucleotide position 7472 (7472insC), in the mtDNA tRNASer(UCN) gene. This mutation, which affects the variable loop and TJC stem of the predicted tRNASer(UCN) cloverleaf, has repeatedly been reported in mitochondrial syndromes [8–11]. As shown in Fig. 1, quantitative XcmIspecific restriction fragment length polymorphism (RFLP) analysis, performed according to Tiranti et al. [8], showed that the mutation was 85% heteroplasmic in muscle and 75% heteroplasmic in blood lymphocyte mtDNA of the patient. The mutation load measured in blood mtDNA ranged from 0 to 30% in asymptomatic maternal members of the pedigree, while it was 60% in both the mother and sister complaining of moderate hearing loss, and 75% in the 25-year-old daughter of the latter subject. This young woman complains of very mild gait instability and restless leg-like syndrome, but neither muscle weakness nor hearing loss. Since, the 7472insC mtDNA mutation may occasionally generate heteroplasmic length variation, sequence analysis of the mtDNA region containing the tRNASer(UCN) gene was performed in the DNA from all the subjects of the family. However, no additional mtDNA variant was ever detected, besides the 7472insC and the wild-type species. Follow up. During the last year, the bilateral hearing loss has worsened. An initial, mild cognitive impairment appeared, with ‘frontal’ reflexes. The tendon reflexes remained brisk in all districts, with tendency to spreading, and on one occasion prolonged clonus of the left foot could be induced by forced dorsiflexion.
3. Discussion In spite of the wealth of papers sustaining the possible role of altered OXPHOS metabolism in the pathogenesis of ALS, the association between mtDNA lesions and MND has persuasively been demonstrated in only a few cases. Comi et al. [12] reported a juvenile-onset ALS-like syndrome, with a predominant involvement of the upper motor neuron, associated with a heteroplasmic microdeletion in the mtDNA gene encoding ND1, a protein subunit of complex I. More recently. Mancuso et al. [13] reported the presence of muscle-specific mtDNA depletion in a SMA type I-like floppy baby. Here, we have shown that Hirayama disease, a very rare, focal MND syndrome, predominantly affecting the lower motor neurons of cervical metamers can be due to a well known pathogenic mtDNA mutation. A causative relation between mitochondrial dysfunction and MND in our patient is supported by the following evidence. First, monomelic amyotrophy was associated with subclinical signs of a more diffuse mitochondrial myopathy, which was documented histologically in the left quadriceps, an apparently non-affected muscular district. Second, the neurological syndrome was associated
725
with maternally inherited hearing loss, a frequent sign of mitochondrial disease. Third, a heteroplasmic mutation, the 7472insC mutation in the tRNASer(UCN) gene, was found in both patient and maternal relatives, with a concordance between mutation load and clinical severity. This mutation was first reported in a large maternal lineage originating from Sicily, complaining of sensorineural hearing loss and, in the most severely affected individuals, ataxia and focal myoclonus [8]. The same mutation was later reported in families or single individuals with a MERRF-like syndrome [9], Epilepsia Partialis Continua [10], and non-syndromic, post-lingual hearing loss [11]. A defect in aminocylation of the tRNASer(UCN) was demonstrated in homoplasmic mutant cybrids [14]. In spite of the wide range of neurological syndromes associated with the 7472insC mutation, in all cases hearing loss was the first and more widespread complaint. Hearing loss was present also in individuals with relatively low mutation loads, while additional signs ensued only when the mutation was homoplasmic or nearly so. This relatively benign behavior of the 7472insC mutation is confirmed by the mild reduction of the respiratory enzyme activities, usually restricted to cytochrome c oxidase, found in most of the reported patients, including the present one, by the absence of ragged-red fibers in the muscle biopsies, and by the very mild effects documented in biochemical assays as well as in measurements on mtDNA transcription and translation, performed in homoplasmic mutant cybrids. We candidly admit that familial hearing loss was not mentioned while taking the patient’s history, and it was overlooked in the first examination of the patient. Only the later appearance of subtle changes at the EMG prompted us to suspect a mitochondrial disease in an otherwise typical monomelic amyotrophy that had been for long labeled as Hirayama disease. The very recent ensue, or accentuation, of additional signs, including frontal and (mild) upper motor neuron involvement, is in agreement with a more diffuse, slowly progressive syndrome, as frequently observed in mitochondrial disease. Finally, an unusual, very mild neurological syndrome was identified in a patient’s niece with high levels of mutation in blood. The possible causative relation between clinical and molecular findings is under investigation.
Acknowledgements We are indebted to Ms B. Geehan for revising the manuscript. Supported by Fondazione Telethon-Italy (grant n. GGP030039), Fondazione Pierfranco e Luisa Mariani (Ricerca 2000), Ricerca Finalizzata Ministero della Salute RF-2002/158, Fondazione Cariplo, and MitEuro network grant from the European Union Framework Program 5.
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V. Fetoni et al. / Neuromuscular Disorders 14 (2004) 723–726
References [1] Hirayama K. Juvenile progressive muscular atrophy localized in the hand and forearm: observations in 38 cases. Clin Neurol (Tokyo) 1972;12:13–24. [2] Schlegel U, Jerusalem F, Tackmann W, Cordt A, Tsuda Y. Benign juvenile focal muscular atrophy of upper extremities: a familial case. J Neurol Sci 1987;80:351–3. [3] Gucuyener K, Aysun S, Topaloglu H, Inan L, Varli K. Monomelic amyotrophy in siblings. Pediat Neurol 1991;7:220–2. [4] Dubowitz V:. Muscle biopsy: a practical approach. London: BailliereTindall; 1985. [5] Darley-Usmar VM, Rickwood D, Wilson MT, editors. Mitochondria, a practical approach. Washington DC: IRL Press; 1987. [6] Torroni A, Rengo C, Guida V, Cruciani F, Sellitto D, Coppa A, Calderon FL, Simionati B, Valle G, Richards M, Macaulay V, Scozzari R. Do the four clades of the mtDNA haplogroup L2 evolve at different rates? Am J Hum Genet 2001;69:1348–56. [7] MITOMAP: a human mitochondrial genome database. http://www. mitomap.org; 2004. [8] Tiranti V, Chariot P, Carella F, Toscano A, Soliveri P, Girlanda P, Carrara F, Fratta GM, Reid FM, Mariotti C, Zeviani M. Inherited hearing loss, ataxia and myoclonus associated with a novel point mutation in mitochondrial tRNASer(UCN) gene. Hum Mol Genet 1995; 4:1421–7. [9] Jaksch M, Klopstock T, Kurlemann G, Dorner M, Hofmann S, Kleinle S, Hegemann S, Weissert M, Muller-Hocker J, Pongratz D,
[10]
[11]
[12]
[13]
[14]
Gerbitz KD. Myoclonus epilepsy and mitochondrial myopathy associated with mutations in the tRNA(Ser(UCN)) gene. Ann Neurol 1998;44:635–40. Schuelke M, Bakker M, Stoltenburg G, Sperner J, von Moers A. Epilepsia partialis continua associated with a homoplasmic mitochondrial tRNA(Ser(UCN)) mutation. Ann Neurol 1998;44: 700–4. Verhoeven K, Ensink RJ, Tiranti V, Huygen PL, Johnson DF, Schatteman I, Van Laer L, Verstreken M, Van de Heyning P, FischelGhodsian N, Zeviani M, Cremers CW, Willems PJ, Van Camp G. Hearing impairment and neurological dysfunction associated with a mutation in the mitochondrial tRNASer(UCN) gene. Eur J Hum Genet 1999;7:45–51. Comi GP, Bordoni A, Salani S, Franceschina L, Sciacco M, Prelle A, Fortunato F, Zeviani M, Napoli L, Bresolin N, Moggio M, Ausenda CD, Taanman JW, Scarlato G. Cytochrome c oxidase subunit I microdeletion in a patient with motor neuron disease. Ann Neurol 1998;43:110–6. Mancuso M, Salviati L, Sacconi S, Otaegui D, Camano P, Marina A, Bacman S, Moraes CT, Carlo JR, Garcia M, Garcia-Alvarez M, Monzon L, Naini AB, Hirano M, Bonilla E, Taratuto AL, DiMauro S, Vu TH. Mitochondrial DNA depletion: mutations in thymidine kinase gene with myopathy and SMA. Neurology 2002;59:1197–202. Toompuu M, Yasukawa T, Suzuki T, Hakkinen T, Spelbrink JN, Watanabe K, Jacobs HT. The 7472insC mitochondrial DNA mutation impairs the synthesis and extent of aminoacylation of tRNASer(UCN) but not its structure or rate of turnover. J Biol Chem 2002;277: 22240–50.
Case report
Monomelic amyotrophy associated with the 7472insC mutation in the mtDNA tRNASer(UCN) gene Vincenza Fetonia, Egill Briemb, Franco Carrarab, Marina Morac, Massimo Zevianib,1,* b
a Unit of Neurology, Public Health Hospital, Melegnano (Milan), Italy Unit of Molecular Neurogenetics—Pierfranco and Luisa Mariani Center for the Study of Children’s Mitochondrial Disorders, National Neurological Institute ‘Carlo Besta’, via Temolo 4, Milan 20133, Italy c Unit of Neuromuscular Disorders, National Neurological Institute ‘Carlo Besta’, via Temolo 4, Milan 20133, Italy
Received 8 April 2004; received in revised form 5 July 2004; accepted 8 July 2004
Abstract We describe a 49-year-old male patient who experienced progressive amyotrophy with no sensorial abnormality in the left arm since 45 years of age. The neuromuscular syndrome was identical to that known as Hirayama disease, a rare form of focal lower motor neuron disease affecting the C7–C8–T1 metamers of the spinal cord. Asymmetric neurosensorial hearing loss was present since age 35 in the patient, and was also documented in an elder sister and in the mother. A muscle biopsy showed cytochrome c oxidase (COX) negative fibers but no ragged-red fibers, and mild reduction of COX was confirmed biochemically. The patient was found to have high levels of a known pathogenic mutation of mtDNA, the 7472insC in the gene encoding the tRNASer(UCN). Investigation on several family members showed a correlation between mutation load and clinical severity. This is the second report documenting the association of lower motor neurone involvement with a specific mtDNA. q 2004 Elsevier B.V. All rights reserved.
1. Introduction Monomelic amyotrophy (Hirayama disease, MIM %602440) is a rare form of motor neuron disease (MND) affecting a single, usually upper, limb [1]. Focal, monolateral lower motor neuron degeneration is believed to occur in the C7–T1 metamers. ‘Oblique amyotrophy’ is a descriptive term to emphasize the sparing of the brachioradialis muscle in the forearm of these patients. After a subacute onset, the course of the disease is stable or slowly progressive. Late involvement of the shoulder or contralateral limb has rarely been reported. The etiology of the syndrome, which is more frequent in young adult males, is unknown. Chronic compression of the cervical spinal cord by a thickened and inelastic dura mater has been hypothesized as the pathogenetic mechanism in a few MRI-documented cases. Several patients originated from * Corresponding author. Tel.: C39-02-2394630; fax: C39-02-2394619. E-mail addresses: [email protected] (M. Zeviani), [email protected] (M. Zeviani). 1 URL: www.mitopedia.org. 0960-8966/$ - see front matter q 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nmd.2004.07.002
Eastern India, which suggests that specific environmental factors, ethnic background, or cultural and behavioral habits may influence the susceptibility to disease. A genetic cause is also suggested by the observation of rare familial cases [2,3]. We report on an Italian patient with adult-onset monomelic amyotrophy associated with a known pathogenic mutation of mtDNA, the 7472insC in the gene encoding the tRNASer(UCN).
2. Case report The proband, a 49-year-old man, is the third of five siblings born from non-consanguineous parents (Fig. 1). His father, deceased at 78 years, suffered from non-insulin dependent diabetes mellitus (NIDDM); the mother, now 88, and an elder sister, now 51, are both suffering of moderate, bilateral neurosensory hearing loss. At age 45, he started complaining of rapidly progressive weakness and wasting of the left upper limb, accompanied
724
V. Fetoni et al. / Neuromuscular Disorders 14 (2004) 723–726
Fig. 2. Histoenzymatic stainings on skeletal muscle consecutive sections. Left panel, succinate dehydrogenase (SDH). Right panel, cytochrome c oxidase (COX). The asterisks indicate COX-negative fibres. !200.
Fig. 1. Pedigree. A black symbol indicates the proband. Half-blackened symbols indicate subjects with hearing loss. A shaded symbol indicates a subject with mild gait instability and a ‘restless-leg like’ syndrome (see text). The percentage of mutation loads in muscle (M) or lymphocyte (L) mtDNA are also indicated. A query point indicates subjects that were not analyzed.
by cramps and tremor, with no sensorial abnormality. During the following 4 years, the muscle symptoms have remained relatively stable. Before the onset of the neuromuscular problems, the only reported complaint was a non-syndromic bilateral neurosensorial hearing loss, more severe in the left ear, which was documented by audiometric examination at age 39. At age 48 he developed NIDDM, controlled by low-glucose diet. When first examined at age 45, the patient had a severe monomelic amyotrophy affecting the C7–C8–T1 left metamers with fasciculations and coarse tremor of the fingers. Severe weakness and hypotrophy involved the interosseous muscles of the hand, the dorsal and flexor muscles of the forearm, with sparing of the brachioradialis, and the extensor muscles of the arm, including the triceps brachii, while the biceps brachii was spared. Apart from the absence of the left tricipital reflex, the tendon reflexes were brisk in all four limbs. The neuromuscular symptoms have hitherto remained stable although occasional fasciculations were recently observed in the contralateral arm. An EMG examination at age 46 showed a neurogenic pattern in the left C6–C7–C8 metamers, characterized by signs of active denervation with spontaneous electric activity (fasciculation potentials), and high-amplitude and prolonged motor potentials during voluntary contraction of the flexor muscles of the forearm and extensor muscles of the arm. The conduction velocity and composite motor amplitude potentials (CMAP) were both normal in the same districts, which excludes the presence of both demyelination and conduction blocks. Brain and cervical MRI were normal, with no sign of compression of the cervical spinal cord. Evoked Motor Potentials, the EEG and the CSF examination were also normal, including the search for oligoclonal bands. The following laboratory tests were normal as well: serum CK, lactic acid, parathyroid hormone, T3, T4, TSH hormones, alpha-fetoprotein, carcino-embryonal antigen, prostatic serum antigen,
and electrolytes. Search for anti-borrelia, anti-GM1, and autoantibodies was negative. A second EMG, performed at age 48, confirmed the neurogenic pattern on the left side, involving the C7–C8–T1 metamers. However, the presence of low-voltage potentials in the C5–C6 metamers on both sides, corresponding to the deltoid muscles, suggested a concomitant, myogenic abnormality, and prompted us to perform a muscle biopsy in the left quadriceps. Morphological analysis of skeletal muscle and biochemical assays of the individual respiratory complexes on muscle homogenate were carried out as described [4,5]. In addition to signs of denervation, such as variation in the fiber size and a tendency to type grouping, the light microscopy examination disclosed the presence of a few cytochrome c oxidase negative fibers (Fig. 2). Some fibers were also hyperreactive to succinate dehydrogenase. The latter finding demonstrates that, in spite of the absence of obvious ragged-red fibers at the modified trichrome Gomori staining, some proliferation of mitochondria occurred in the skeletal muscle of the patient, as typically seen in mitochondrial myopathies. Biochemical analysis of the respiratory chain complexes, performed on muscle homogenate, revealed a mild reduction of cytochrome c oxidase, while the other enzyme activities were within the control ranges (Table 1). Nucleotide sequence analysis was then performed on eleven overlapping PCR fragments encompassing the entire mtDNA molecule [6]. The data were compared to the revised Cambridge sequence of human mtDNA [7]. In addition to a few homoplasmic changes that were already reported as non-pathogenic polymorphisms (not shown), we identified a heteroplasmic Table 1 Respiratory chain activities in muscle homogenate
Complex I/CS Complex II/CS Complex III/CS Complex IV/CS Complex V/CS Succinate dehydrogenase Citrate synthase
Patient
Control range
21.3 31.3 71.7 64 145 21.3 105
15–25 15–28 70–150 80–180 75–180 10–20 80–210
Specific activities are expressed as nmoles/min/mg protein.
V. Fetoni et al. / Neuromuscular Disorders 14 (2004) 723–726
mutation, consisting in the insertion of a cytosine at nucleotide position 7472 (7472insC), in the mtDNA tRNASer(UCN) gene. This mutation, which affects the variable loop and TJC stem of the predicted tRNASer(UCN) cloverleaf, has repeatedly been reported in mitochondrial syndromes [8–11]. As shown in Fig. 1, quantitative XcmIspecific restriction fragment length polymorphism (RFLP) analysis, performed according to Tiranti et al. [8], showed that the mutation was 85% heteroplasmic in muscle and 75% heteroplasmic in blood lymphocyte mtDNA of the patient. The mutation load measured in blood mtDNA ranged from 0 to 30% in asymptomatic maternal members of the pedigree, while it was 60% in both the mother and sister complaining of moderate hearing loss, and 75% in the 25-year-old daughter of the latter subject. This young woman complains of very mild gait instability and restless leg-like syndrome, but neither muscle weakness nor hearing loss. Since, the 7472insC mtDNA mutation may occasionally generate heteroplasmic length variation, sequence analysis of the mtDNA region containing the tRNASer(UCN) gene was performed in the DNA from all the subjects of the family. However, no additional mtDNA variant was ever detected, besides the 7472insC and the wild-type species. Follow up. During the last year, the bilateral hearing loss has worsened. An initial, mild cognitive impairment appeared, with ‘frontal’ reflexes. The tendon reflexes remained brisk in all districts, with tendency to spreading, and on one occasion prolonged clonus of the left foot could be induced by forced dorsiflexion.
3. Discussion In spite of the wealth of papers sustaining the possible role of altered OXPHOS metabolism in the pathogenesis of ALS, the association between mtDNA lesions and MND has persuasively been demonstrated in only a few cases. Comi et al. [12] reported a juvenile-onset ALS-like syndrome, with a predominant involvement of the upper motor neuron, associated with a heteroplasmic microdeletion in the mtDNA gene encoding ND1, a protein subunit of complex I. More recently. Mancuso et al. [13] reported the presence of muscle-specific mtDNA depletion in a SMA type I-like floppy baby. Here, we have shown that Hirayama disease, a very rare, focal MND syndrome, predominantly affecting the lower motor neurons of cervical metamers can be due to a well known pathogenic mtDNA mutation. A causative relation between mitochondrial dysfunction and MND in our patient is supported by the following evidence. First, monomelic amyotrophy was associated with subclinical signs of a more diffuse mitochondrial myopathy, which was documented histologically in the left quadriceps, an apparently non-affected muscular district. Second, the neurological syndrome was associated
725
with maternally inherited hearing loss, a frequent sign of mitochondrial disease. Third, a heteroplasmic mutation, the 7472insC mutation in the tRNASer(UCN) gene, was found in both patient and maternal relatives, with a concordance between mutation load and clinical severity. This mutation was first reported in a large maternal lineage originating from Sicily, complaining of sensorineural hearing loss and, in the most severely affected individuals, ataxia and focal myoclonus [8]. The same mutation was later reported in families or single individuals with a MERRF-like syndrome [9], Epilepsia Partialis Continua [10], and non-syndromic, post-lingual hearing loss [11]. A defect in aminocylation of the tRNASer(UCN) was demonstrated in homoplasmic mutant cybrids [14]. In spite of the wide range of neurological syndromes associated with the 7472insC mutation, in all cases hearing loss was the first and more widespread complaint. Hearing loss was present also in individuals with relatively low mutation loads, while additional signs ensued only when the mutation was homoplasmic or nearly so. This relatively benign behavior of the 7472insC mutation is confirmed by the mild reduction of the respiratory enzyme activities, usually restricted to cytochrome c oxidase, found in most of the reported patients, including the present one, by the absence of ragged-red fibers in the muscle biopsies, and by the very mild effects documented in biochemical assays as well as in measurements on mtDNA transcription and translation, performed in homoplasmic mutant cybrids. We candidly admit that familial hearing loss was not mentioned while taking the patient’s history, and it was overlooked in the first examination of the patient. Only the later appearance of subtle changes at the EMG prompted us to suspect a mitochondrial disease in an otherwise typical monomelic amyotrophy that had been for long labeled as Hirayama disease. The very recent ensue, or accentuation, of additional signs, including frontal and (mild) upper motor neuron involvement, is in agreement with a more diffuse, slowly progressive syndrome, as frequently observed in mitochondrial disease. Finally, an unusual, very mild neurological syndrome was identified in a patient’s niece with high levels of mutation in blood. The possible causative relation between clinical and molecular findings is under investigation.
Acknowledgements We are indebted to Ms B. Geehan for revising the manuscript. Supported by Fondazione Telethon-Italy (grant n. GGP030039), Fondazione Pierfranco e Luisa Mariani (Ricerca 2000), Ricerca Finalizzata Ministero della Salute RF-2002/158, Fondazione Cariplo, and MitEuro network grant from the European Union Framework Program 5.
726
V. Fetoni et al. / Neuromuscular Disorders 14 (2004) 723–726
References [1] Hirayama K. Juvenile progressive muscular atrophy localized in the hand and forearm: observations in 38 cases. Clin Neurol (Tokyo) 1972;12:13–24. [2] Schlegel U, Jerusalem F, Tackmann W, Cordt A, Tsuda Y. Benign juvenile focal muscular atrophy of upper extremities: a familial case. J Neurol Sci 1987;80:351–3. [3] Gucuyener K, Aysun S, Topaloglu H, Inan L, Varli K. Monomelic amyotrophy in siblings. Pediat Neurol 1991;7:220–2. [4] Dubowitz V:. Muscle biopsy: a practical approach. London: BailliereTindall; 1985. [5] Darley-Usmar VM, Rickwood D, Wilson MT, editors. Mitochondria, a practical approach. Washington DC: IRL Press; 1987. [6] Torroni A, Rengo C, Guida V, Cruciani F, Sellitto D, Coppa A, Calderon FL, Simionati B, Valle G, Richards M, Macaulay V, Scozzari R. Do the four clades of the mtDNA haplogroup L2 evolve at different rates? Am J Hum Genet 2001;69:1348–56. [7] MITOMAP: a human mitochondrial genome database. http://www. mitomap.org; 2004. [8] Tiranti V, Chariot P, Carella F, Toscano A, Soliveri P, Girlanda P, Carrara F, Fratta GM, Reid FM, Mariotti C, Zeviani M. Inherited hearing loss, ataxia and myoclonus associated with a novel point mutation in mitochondrial tRNASer(UCN) gene. Hum Mol Genet 1995; 4:1421–7. [9] Jaksch M, Klopstock T, Kurlemann G, Dorner M, Hofmann S, Kleinle S, Hegemann S, Weissert M, Muller-Hocker J, Pongratz D,
[10]
[11]
[12]
[13]
[14]
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