Clinical and neuropathological findings in patients with TACO1 mutations

Neuromuscular Disorders 20 (2010) 720–724

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Clinical and neuropathological findings in patients with TACO1 mutations Jürgen Seeger a, Bertold Schrank a, Angela Pyle b,e, Rolf Stucka c, Ulrich Lörcher a, Solvig Müller-Ziermann d, Angela Abicht c,d, Birgit Czermin d, Elke Holinski-Feder d, Hanns Lochmüller e, Rita Horvath b,d,e,* a

Deutsche Klinik für Diagnostik, Wiesbaden, Germany Mitochondrial Research Group, Newcastle University, Newcastle upon Tyne, UK c Friedrich-Baur-Institut, Ludwig-Maximilians University, Munich, Germany d Medical Genetic Center, Munich, Germany e Institute of Human Genetics, Newcastle University, Newcastle upon Tyne, UK b

a r t i c l e

i n f o

Article history: Received 24 February 2010 Received in revised form 21 April 2010 Accepted 29 June 2010

Keywords: Leigh syndrome Cytochrome c oxidase Translation TACO1

a b s t r a c t We have recently identified mutations in the translation activator of cytochrome c oxidase 1 (TACO1) gene, leading to cytochrome c oxidase (COX) deficiency. Here, we report the clinical and neuroimaging findings of five members of a big consanguinous family homozygous for c.472insC in TACO1. All 5 patients had an uneventful early childhood and a subtle onset, slowly progressive cognitive dysfunction, dystonia or visual impairment between ages 4 and 16 years. Affected girls had a milder phenotype and preserved ambulation into the late twenties. Brain MRI revealed bilateral, symmetric lesions of the basal ganglia in all affected family members, but less prominent in girls. TACO1 analysis showed no mutations in 17 patients with juvenile-onset Leigh syndrome and isolated COX or combined respiratory chain deficiency, indicating that TACO1 mutations are a rare cause of Leigh syndrome. Ó 2010 Elsevier B.V. All rights reserved.

1. Introduction Cytochrome c oxidase (COX or complex IV), the terminal enzyme of the respiratory chain (RC), catalyzes the reduction of molecular oxygen by reduced cytochrome c [1]. Three highly conserved mtDNA-encoded subunits (COX I–III) form the catalytic core of the enzyme and 10 nuclear subunits are thought to modify or stabilize the complex [2,3]. Pathogenic mutations in all three mtDNA-encoded subunits have been identified whereas a single homozygous mutation was detected in the nuclear subunit gene COX6B1 in a consanguinous family [4]. Mutations in nuclear genes involved in COX assembly (SURF1, SCO2, SCO1, COX10, COX15) have been described with severe early infantile phenotypes [5]. While several COX assembly factors with roles in the synthesis and assembly of prosthetic groups and in chaperoning COX subunits have been described [6], very little is known about the regulation of the synthesis of the individual mitochondrial-encoded COX subunits in humans. To date, only one human protein (LRPPRC) has been reported to be involved in the stabilization and translation of the mRNAs for both COX I and COX III in mammals. Mutations in LRPPRC are the cause of the French–Canadian Leigh syndrome [7]. * Corresponding author. Address: Mitochondrial Research Group, Institute for Aging and Health, Newcastle University, Framlington Place, NE2 4HH, UK. Tel.: +44 191 222 5982; fax: +44 191 282 4373. E-mail address: [email protected] (R. Horvath). 0960-8966/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nmd.2010.06.017

We have recently identified and characterized the first specific mammalian mitochondrial translational activator, TACO1 that is necessary for the synthesis of full length COX I [8]. Here, we report the detailed clinical, histological, and biochemical findings in 5 patients in a consanguinous family carrying a homozygous mutation in TACO1.

2. Patients and methods The clinical description of the family was briefly reported previously. [8] The detailed clinical presentation of the 5 patients is summarized in the Table 1. All 5 patients belong to a single consanguineous family of Kurdish ethnic background, but living in Germany.

2.1. Patient 1 Patient 1, a 20-year-old man was born after an uneventful pregnancy by normal delivery. After normal early development, unsteadiness and speech difficulties were noted at 5 years of age, hearing was normal. On clinical examination at age 10 years, he was small (weight and height <3rd percentile for Turkish children, head circumference normal). He had bilateral optic atrophy, facial hypotonia, dysarthria, mild dysphagia and spastic tetraparesis with pyramidal signs and dystonic movements. He could sit unaided,

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J. Seeger et al. / Neuromuscular Disorders 20 (2010) 720–724 Table 1 The clinical presentation of the 5 patients is summarized in the table. Patient At age

Onset

Motor symptoms

Speech

Behavioural problems

Optic atrophy

Stature percentile

School performance

Functional status (ADL)

P1 (M) 10 years

Spastic tetraparesis

Dysarthria

None

Yes

<3rd

School for mentally retarded

Dependent

P2 (F) 18 years

5 years, speech and gait problems 13 years, learning difficulties

Not known

3rd–10th

7 years regular school but no graduation

Requires assistance

4 years, gait problem 7 years, learning difficulties 6 years visual impairment

Reduced fluency, dysarthria Reduced fluency Normal

None

P3 (M) 12 years P4 (F) 15 years P5 (F) 23 years

Hemidystonia, bradykinesia, pyramidal signs Mildly spastic gait, dystonia Mild pyramidal signs

Perseverations

No

3rd–10th

None

Paraphasia reduced fluency

Perseveration, negligent, temper tantrums

25th– 50th 10th– 25th

Requires supervision Normal

None

Not known Yes

School for mentally retarded School for learning disabled School for learning disabled from grade 7

but could not stand or walk. Cognitive functions were moderately impaired. Laboratory analysis showed increased serum lactate (4.1 mmol/ L, normal <2) and pyruvate (1.6 mg/dL, normal <0.7) as well as CSF lactate (3.2 mmol/L, normal <2) and a tubulopathy with mild aminoaciduria. Other laboratory tests including CSF protein were normal. At age 20 years, he had spastic dystonia and was wheelchairbound. He lost his active speech, but continued to understand spoken language. Supplementation with coenzyme Q10 and carnitine had no effect. 2.2. Patient 2 This 26 year-old woman’s first symptoms started at 14– 16 years with involuntary movements of the left hand and slightly slurred speech. At 13 years, she had discontinued school without graduating. On examination at 18 years of age, she was small (weight and height 3rd–10th percentile, normal head circumference), had normal eye movements, no visual loss, but facial hypotonia and slurred speech. She had mild left-sided spastic hemiparesis and hemidystonia, dysdiadochokinesis, but normal gait. Cognitive function was impaired. She never reached fluency in German language. Laboratory analysis including CK (80 U/L, normal <200) was normal. Electrophysiological and cardiological studies showed normal results. At age 26 years, she had marked spastic tetraparesis and dystonia but she was still able to walk. She lives with her parents and has no social contacts outside the family. She received supplementation with Coenzyme Q10, carnitine, vitamin C and creatine without any clinical benefit. 2.3. Patient 3 This 12.5-year-old-boy had normal early development but poor weight gain and gait instability was noted at 4 years of age. On examination he was small (weight and height at 3rd–10th percentile; head circumference normal). His vision and eye movements were normal and his speech was normal for his age. He had brisk reflexes with normal tone and strength, but some dystonia was observed. He could not jump or run fast and his gait was unstable. Cognitive functions were normal. Laboratory analysis (serum lactate 0.4 mmol/L, normal <2.0; CK 55 U/L, normal0 <200) and ophthalmological as well as cardiological examination were normal. At age 12.5 years ambulation was still possible, although gait instability, clumsiness and dystonic symptoms had progressed. Cognitive functions were impaired (mild mental retardation).

Requires supervision

2.4. Patient 4 This 15-year-old girl had no complains, and her investigation was prompted only by the genetic condition within the family. On clinical examination at age 15 years she had normal weight (10–25th percentile), height (25–50th percentile) and head circumference. She had normal eye movements and good visual acuity. The face was hypotonic. She had no weakness and had normal gait. Neurological examination showed mild bilateral dysmetria, brisk reflexes with pyramidal signs and bilateral hammer toes. Her speech was normal. She had a learning disability and had attended a special school from the first grade with good results. 2.5. Patient 5 This 23-year-old woman was the first child of healthy consanguineous parents and a cousin of patients 1–4. She has 4 healthy adult siblings. The parents reported visual impairment since 6 years of age. Ophthalmological examination revealed bilateral optic atrophy. In the following years, speech impairment, learning difficulties and exercise intolerance with muscle pain became apparent. At 23 years of age (weight 55 kg, height 155 cm, 10– 25th percentile) she had bilateral optic atrophy (visual acuity 0.2/0.12) and cognitive decline with behavioral abnormalities, perseveration and some degree of expressive aphasia, but no other neurological signs. Laboratory analysis including CK (85 U/L, normal <200) was normal. 2.6. Brain MRI Proton density, FLAIR and T1/2 weighted sequences were performed on a Philips Gyroscan 1.5 T (Patient 1), Siemens Symphony 1,5 T (Patient 2 at 26 years, Patient 3, Patient 5) and a GE Genesis Sigma 1,5 T (Patient 4). The MRI studies of the patients were due to the courtesy of the Institute of Radiology, Klinikum Offenbach and the Radiological Center Offenbach/Dietzenbach. 2.7. Morphology and biochemistry of skeletal muscle Morphology and respiratory chain complexes I–IV activities in skeletal muscle were performed by standard methods. 2.8. DNA analysis DNA extraction from blood of the patients and other family members was done according to standard protocols (Qiagen, Hildesheim, Germany). TACO1 analysis was performed in genomic DNA as described. [8] Segregation analysis of the mutation within

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Fig. 1. MRI scans of the affected family members demonstrate a wide range of abnormalities. Typical hyperintense putaminal lesions on T2 and FLAIR images are apparent in all affected patients to a variable degree with evidence of cystic changes in the most severely affected patients (patient 1 (A) and 3 (C), FLAIR). The lesser affected female patient (patient 2) shows less cystic changes (B) than her more severely affected brothers. The female patient with predominant speech and behavioural disorder (patient 5, E) only shows minor putaminal hyperintensities and some mild cortical atrophy. The least affected female patient (patient 4, D) shows small T2 signal hyperintensities bilaterally in the putamen and caudate nucleus. In addition, the most severely affected wheelchair-bound patient (patient 1) has a partially cystic periventricular leukoencephalopathy (A), while patient 2 and patient 3 only have mild white matter changes (B and C).

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the family was done by RFLP analysis with primers specific for exon 3 of TACO1, followed by digestion with MwoI as described [8]. 3. Results 3.1. Brain MRI Brain MRI of patients 1 (age 10 years) (Fig. 1A), 2 (age 18 years) (data not shown) and 3 (age 4 years) (Fig. 1C) showed bilateral, symmetric hyperintense lesions in the basal ganglia and the frontal subcortical areas (T2/PD/FLAIR). Brainstem and cerebellum were normal. Follow-up MRI of patient 2 at age 26 years (Fig. 1B) noted a progression of lesions especially in the subcortical white matter and cystic changes in the putamen and globus pallidum. Small T2 signal intensities were noted bilaterally in the putamen and caudate nuclei on brain MRI of patient 4 at 15 years of age (Fig. 1D). A moderate cortical atrophy and a small T2 signal intensity in the right putamen were detected on MRI of patient 5 at age 23 (Fig. 1E). 3.2. Morphology and biochemistry of skeletal muscle Muscle biopsy of patient 1 at 10 years of age showed a few hypotrophic fibers and a generalized COX deficiency in all fibres but no ragged red fibers or SDH hyperreactive fibers. Biochemical analysis of the respiratory chain enzyme complexes I–IV and pyruvate dehydrogenase showed a severe isolated COX deficiency with approximately 15% residual activity (12 U/g non collagen protein (gNCP), normal 90–281: 0.17 U/U citrate synthase (UCS), normal 0.90–4.70), the activity of the other enzymes were within normal range. COX activity was also low in fibroblasts (3.4 U/gNCP, normal 5.1–22; 0.22 U/UCS, normal 0.34–1.24). 3.3. DNA analysis Sequence analysis detected the first mutation in TACO1 causing human disease, a homozygous one base-pair insertion at position 472 (c.472insC), resulting in a frame-shift and creating a premature stop codon. [8] The mutation segregated with the phenotype in the pedigree; all affected individuals carried the homozygous mutation, both parents were heterozygous, while the healthy siblings were either heterozygous or wild-type. Systematic screening for TACO1 mutations in 10 other individuals with isolated COX deficiency from families of different ethnic backgrounds and from 7 patients with juvenile-onset Leigh syndrome and combined RC deficiency revealed no mutation. 4. Discussion We have recently identified and characterized TACO1, a novel component of the mammalian mitochondrial translation apparatus. Here, we describe the clinical presentation of 5 patients from a consanguineous family, homozygous for a frame-shift mutation in TACO1. All patients had a juvenile-onset Leigh-like disease although the severity of symptoms shows wide variability. Affected patients were all relatively thin, small stature (<3rd to >25th percentile) and developed slowly progressive neurological deficits including bilateral optic atrophy, spastic tetraparesis, dystonia, slurred speech and a moderate cognitive deficit. While receptive language skills were reasonably well preserved, expressive language became variably impaired (dysarthria and/or aphasia) in all except the youngest female patient (15 years). Motor impairment seemed to correlate with putaminal lesions on cranial MRI but there was no imaging correlate to language impairment. Interestingly, the 2 boys had onset of symptoms with gait distur-

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bance at age 4 and 5 years and lost ambulation around age 10– 12.5 years, while the three affected girls had first motor symptoms in their teens and still ambulatory into their twenties; they had primarily cognitive and behavioral problems starting during their first school years. Patient 5 suffered from visual impairment due to optic atrophy at initial presentation. The relatively late onset (4–16 years) and slow progression of Leigh syndrome is rather unusual, especially considering the magnitude of the COX deficiency (15% of control COX activity in the index patient’s muscle). Patients with all other previously described mutations in COX assembly genes (SURF1, SCO1, SCO2, COX10, COX15, LRPPRC) generally present with clinical disease very early in life (first weeks or months), and have a rapidly deteriorating course leading to early death [5]. In patients 1–4 brain MRI showed bilateral, symmetric hyperintense lesions of the basal ganglia with variable involvement of the subcortical white matter. Corresponding to clinical severity, the intensity of the MRI changes was less severe in the girls and asymmetrical in patient 5. Although suggestive of a true gender effect the small number of affected patients prohibits statistical validation of such an effect. We screened for mutations in TACO1 in other patients with isolated COX deficiency and mitochondrial encephalomyopathy and could not identify any other case with TACO1 deficiency. We therefore assume that this defect is a rare cause of isolated COX deficiency. Although the combination of spasticity, dystonia and learning difficulties in juvenile age may indicate other diagnostic possibilities, we believe that the Leigh-like lesions on MRI are strong indicators of a mitochondrial etiology and should prompt initiating biochemical investigations. Although a strictly isolated COX deficiency was detected in our index patient, there is in vitro evidence, that TACO1 mutations may also have milder effects on the translation of other mitochondrial proteins. In fact, TACO1 is also part of a higher molecular weight complex possibly together with other mitochondrial proteins, such as EFTs, a mitochondrial translation elongation factor, suggesting a possible interaction of TACO1 and the mitochondrial translation components. Therefore we extended TACO1 sequencing to patients with juvenile-onset Leigh syndrome and combined RC deficiency, but could not identify any pathological mutations. In summary, we describe the clinical presentation of patients harbouring mutations in TACO1, a new member of nuclear genes causing mitochondrial disease by impairing the translation of a single mitochondrial protein (COX I). Although mutations in TACO1 seem to be a rare cause of isolated COX deficiency, genetic screening in patients is recommended. 5. Disclosure The authors report no conflicts of interest. Acknowledgements We thank Professor Eric A. Shoubridge for the helpful comments on the paper. We thank the patients and their families for contributing to this study. R.H. is supported by the Deutsche Forschungsgemeinschaft HO 2505/2-1, the Newcastle upon Tyne Hospitals NHS Charity (RES0211/7262) and the Academy of Medical Sciences (UK, BH090164) and by the MRC (UK) as part of the MRC Centre for Neuromuscular Diseases. References [1] Taanman JW. Human cytochrome c oxidase: structure, function, and deficiency. J Bioenerg Biomembr 1997;29:151–63.

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