Novel mitochondrial tRNALeu(CUN) transition and D4Z4 partial deletion in a patient with a facioscapulohumeral phenotype

doi:10.1016/j.nmd.2007.12.005

Neuromuscular Disorders

Volume 18, Issue 3, March 2008, Pages 204-209

https://doi.org/10.1016/j.nmd.2007.12.005 Get rights and content

Abstract

Point mutations in mtDNA-encoded tRNA genes frequently cause isolated myopathies but rarely cause the facioscapulohumeral phenotype.

We report on a patient affected with chronic progressive weakness of facioscapulohumeral/peroneal muscles whose muscle biopsy showed a mitochondrial myopathy. mtDNA direct sequencing and RFLP analysis revealed a heteroplasmic transition T12313C which disrupts a conserved site in the TΨC stem of the tRNA^Leu(CUN) gene and fulfills the accepted criteria of pathogenicity.

A partial deletion of the nuclear DNA D4Z4 region with residual repeat sizes of 25 kb was also found in the patient and in her mother.

This is the first reported case of mitochondrial myopathy/facioscapulohumeral muscular dystrophy (FSHD) “double trouble”.

Introduction

Mitochondrial DNA (mtDNA) mutations are associated with a wide spectrum of disorders involving different tissues, particularly brain and muscle [1]. While tRNA^Leu(UUR) is a “hot spot” for mutations that cause different clinical pictures, a relatively small number of pathogenic changes have been reported in the tRNA^Leu(CUN) gene from patients with more homogeneous neurological presentation, such as chronic progressive external ophthalmoplegia and myopathy [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12].

Facioscapulohumeral muscular dystrophy (FSHD), an autosomal dominant neuromuscular disorder, is characterized by progressive weakness of the facial, shoulder girdle and upper limb muscles, often involving peroneal and pelvic girdle muscles. The molecular bases of the disease are unknown, but the disorder is associated with deletions of specific 3.3 kb tandem repeats, termed D4Z4 repeats, on chromosome 4q35 [13]. These deletions lead to inappropriate transcriptional derepression of proximal genes located upstream of D4Z4, including FRG1, FRG2, and adenine nucleotide translocator (ANT1) [13].

We report on a patient with facioscapulohumeral and peroneal muscle weakness who had a new pathogenic mutation in the TΨC stem of the mtDNA tRNA^Leu(CUN) and a partial deletion of the repetitive elements D4Z4 on chromosome 4q35. The clinical and the molecular data are consistent with a diagnosis of mitochondrial myopathy/FSHD “double trouble”.

Section snippets

Patient

A 45-year-old teacher came to our observation for fatigue in lifting her arms above the head and difficulty in walking. She reported incapacity to whistle and scapular winging from adolescence. She did not describe fatigue, myalgia or cramps, even for long trekking, up to 30 years of age. When she was 34 she began complaining of weakness and easy fatigability of the right arm while writing on the blackboard. Two years later she noticed left foot drop and difficulty in climbing stairs.

At 45

Results

Muscle biopsy showed few atrophic fibers, mild focal increase of connective tissue and numerous ragged red fibers (RRFs) (Fig. 1A). Thirty nine percent of the fibers were cytochrome c oxidase (COX)-negative (Fig. 1B); on longitudinal sections the histochemical defect was segmental. All RRFs were COX-negative. Eighty-three percent of the fibers belonged to type 1.

By biochemical analysis COX activity was reduced to 50% the normal value (Table 1).

Sequencing of the 22 mtDNA tRNA genes revealed a

Discussion

This patient came to our observation for long-standing muscle weakness that had an asymmetrical facioscapulohumeral distribution at onset, but eventually involved the left anterior tibial and pelvic girdle muscles.

Although the clinical criteria for FSHD were satisfied [19], quite surprisingly the muscle biopsy showed numerous ragged red and COX deficient fibers. Molecular analysis documented a new transition in the tRNA^Leu(CUN) TΨC stem at nucleotide 12313, but also a deletion of the repetitive

Acknowledgements

The authors thank Drs. C. Angiari, M. Ferrarini, S. Marconi, and F. Taioli from Department of Neurological Sciences and Vision of the University of Verona for their precious help in performing molecular genetic studies.

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Cited by (13)

Rippling muscle disease and facioscapulohumeral dystrophy-like phenotype in a patient carrying a heterozygous CAV3 T78M mutation and a D4Z4 partial deletion: Further evidence for "double trouble" overlapping syndromes
2012, Neuromuscular Disorders
Citation Excerpt :
This is particularly true for FSHD, in which various clinical features have been found in subjects carrying FSHD-sized D4Z4 alleles, including a facial-sparing form of FSHD (SHD) [42], limb-girdle muscular dystrophy [43], distal myopathy [44], asymmetric brachial weakness [43], chronic progressive external ophthalmoplegia [45], asymptomatic hyperCKemia [46], hypertrophic cardiomyopathy [47], adult-onset distal myopathies with rimmed vacuoles [48], isolated axial myopathy with camptocormia and bent spine syndrome [49,50]. In addition, overlapping FSHD phenotypes in which 4q35 deleted D4Z4 mutation is associated with other pathogenic mutations in other genes, have been reported in cases of patients with mitochondrial myopathy/FSHD [51], Becker dystrophy/FSHD [52], Duchenne dystrophy/FSHD [53,54], Leber’s hereditary optic neuropathy/FSHD [55], suggesting a synergistic effect of those simultaneous mutations in reaching disease threshold and determining overlapping phenotypes. In conclusion, our case may represent a further example of such atypical phenotypes in which D4Z4 deletion contributes to pathogenicity of heterozygous CAV3 T78M mutation for the observed myopathic phenotype, resulting in an overlapping syndrome.
We report the first case of a heterozygous T78M mutation in the caveolin-3 gene (CAV3) associated with rippling muscle disease and proximal myopathy. The patient displayed also bilateral winged scapula with limited abduction of upper arms and marked asymmetric atrophy of leg muscles shown by magnetic resonance imaging. Immunohistochemistry on the patient’s muscle biopsy demonstrated a reduction of caveolin-3 staining, compatible with the diagnosis of caveolinopathy. Interestingly, consistent with the possible diagnosis of FSHD, the patient carried a 35 kb D4Z4 allele on chromosome 4q35. We discuss the hypothesis that the two genetic mutations may exert a synergistic effect in determining the phenotype observed in this patient.
Large-scale population analysis challenges the current criteria for the molecular diagnosis of fascioscapulohumeral muscular dystrophy
2012, American Journal of Human Genetics
Citation Excerpt :
In some rare cases, that could be by becoming homozygous20 and doubling the dose of a dominant factor such as DUX4. In others, it might be by the simultaneous heterozygosity for a different and recessive myopathy, as suggested by many reports in which the FSHD contractions are found in association with a second molecular defect.31–44 This possibility is also consistent with previous reports of expression changes of candidate proteins such as CRYM that were associated with FSHD in some families but that were unchanged when other families were examined.
Facioscapulohumeral muscular dystrophy (FSHD) is a common hereditary myopathy causally linked to reduced numbers (≤8) of 3.3 kilobase D4Z4 tandem repeats at 4q35. However, because individuals carrying D4Z4-reduced alleles and no FSHD and patients with FSHD and no short allele have been observed, additional markers have been proposed to support an FSHD molecular diagnosis. In particular a reduction in the number of D4Z4 elements combined with the 4A(159/161/168)PAS haplotype (which provides the possibility of expressing DUX4) is currently used as the genetic signature uniquely associated with FSHD. Here, we analyzed these DNA elements in more than 800 Italian and Brazilian samples of normal individuals unrelated to any FSHD patients. We find that 3% of healthy subjects carry alleles with a reduced number (4–8) of D4Z4 repeats on chromosome 4q and that one-third of these alleles, 1.3%, occur in combination with the 4A161PAS haplotype. We also systematically characterized the 4q35 haplotype in 253 unrelated FSHD patients. We find that only 127 of them (50.1%) carry alleles with 1–8 D4Z4 repeats associated with 4A161PAS, whereas the remaining FSHD probands carry different haplotypes or alleles with a greater number of D4Z4 repeats. The present study shows that the current genetic signature of FSHD is a common polymorphism and that only half of FSHD probands carry this molecular signature. Our results suggest that the genetic basis of FSHD, which is remarkably heterogeneous, should be revisited, because this has important implications for genetic counseling and prenatal diagnosis of at-risk families.
The m.12316G>A mutation in the mitochondrial tRNA<sup>Leu(CUN)</sup> gene is associated with mitochondrial myopathy and respiratory impairment
2010, Journal of the Neurological Sciences
Mitochondrial disorders are often associated with mutations in mitochondrial tRNA. Independent observation of the same molecular defect in unrelated subjects is a generally required proof of pathogenicity. A sporadic case of chronic external ophthalmoplegia (cPEO) with ragged red fibres (RRFs) has been previously related to an m.12316G>A substitution in tRNA^Leu(CUN).
Sequencing muscle-derived mtDNA, we found the m.12316G>A substitution in an adult woman with mitochondrial myopathy and respiratory impairment. Her muscle biopsy presented several cytochrome c oxidase-negative (COX−) fibres, and RRFs as signs of mitochondrial proliferation. Restriction-fragment length polymorphism (RFLP) analysis of the mutation in isolated muscle fibres showed a threshold of at least 60% of mutated mtDNA to determine a COX deficiency phenotype. This second report of the m.12316G>A mutation in a sporadic patient consolidates its pathogenic nature and provides further elements for genetic counselling.
Slowly progressive encephalopathy with hearing loss due to a mutation in the mtDNA tRNA<sup>Leu(CUN)</sup> gene
2010, Journal of the Neurological Sciences
Pathogenic mutations in the tRNA^Leu(UCN) gene of mitochondrial DNA (mtDNA) have been invariably accompanied by skeletal myopathy with or without chronic progressive external ophthalmoplegia (CPEO). We report a young woman with a heteroplasmic m.12276G > A mutation in tRNA^Leu(UCN), who had childhood-onset and slowly progressive encephalopathy with ataxia, cognitive impairment, and hearing loss. Sequencing of the 22 tRNA mitochondrial genes is indicated in all unusual neurological syndromes, even in the absence of maternal inheritance.
Phenotypic Variability among Patients with D4Z4 Reduced Allele Facioscapulohumeral Muscular Dystrophy
2020, JAMA Network Open
Clinical Manifestation of Mitochondrial Disorders in Childhood
2019, Handbook of Mitochondrial Dysfunction

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Novel mitochondrial tRNALeu(CUN) transition and D4Z4 partial deletion in a patient with a facioscapulohumeral phenotype

Abstract

Introduction

Section snippets

Patient

Results

Discussion

Acknowledgements

Biochem Biophys Res Commun

Biochim Biophys Acta

J Neurol Sci

Neuromusc Disord

Cell

Neuromusc Disord

Neuromusc Disord

J Neurol Sci

A heteroplasmic point mutation of mitochondrial tRNALeu(CUN) in non-lymphoid haemopoietic cell lineages from a patient with acquired idiopathic sideroblastic anaemia

Br J Haematol

Exercise intolerance resulting from a muscle-restricted mutation in the mitochondrial tRNALeu(CUN) gene

Ann Med

Tissue dependent co-segregation of the novel pathogenic G12276A mitochondrial tRNA Leu(CUN) mutation with the A185 G D-loop polymorphism

J Med Genet

Classical mitochondrial phenotypes without mtDNA mutations: the possible role of nuclear genes

Neurology

The mitochondrial DNA mutation T12297 C affects a highly conserved nucleotide of tRNA(Leu(CUN)) and is associated with dilated cardiomyopathy

Eur J Hum Genet

A novel heteroplasmic tRNA Leu(CUN) mtDNA point mutation in a sporadic patient with mitochondrial encephalomyopathy segregates rapidly in skeletal muscle and suggests an approach to therapy

Hum Mol Genet

A new mtDNA mutation showing accumulation with time and restriction to skeletal muscle

Am J Hum Genet

Novel mitochondrial tRNA^Leu(CUN) transition and D4Z4 partial deletion in a patient with a facioscapulohumeral phenotype