Clinical and molecular survey in 124 Chinese patients with Leigh or Leigh-like syndrome

Clinical Diagnosis and Treatment of Leigh Syndrome Based on SURF1: Genotype and Phenotype

SURF1 encodes the assembly factor for maintaining the antioxidant of cytochrome c oxidase (COX) stability in the human electron respiratory chain. Mutations in SURF1 can cause Leigh syndrome (LS), a subacute neurodegenerative encephalopathy, characterized by early onset (infancy), grave prognosis, and predominant symptoms presenting in the basal ganglia, thalamus, brainstem, cerebellum, and peripheral nerves. To date, more than sixty different SURF1 mutations have been found to cause SURF1-associated LS; however, the relationship between genotype and phenotype is still unclear. Most SURF1-associated LS courses present as typical LS and cause early mortality (before the age of ten years). However, 10% of the cases present with atypical courses with milder symptoms and increased life expectancy. One reason for this inconsistency may be due to specific duplications or mutations close to the C-terminus of the SURF1 protein appearing to cause less protein decay. Furthermore, the treatment for SURF1-associated LS is unsatisfactory. A ketogenic diet is most often prescribed and has proven to be effective. Supplementing with coenzyme Q and other cofactors is also a common treatment option; however, the results are inconsistent. Importantly, anti-epileptic drugs such as valproate—which cause mitochondrial dysfunction—should be avoided in patients with SURF1-associated LS presenting with seizures.

Clinical exome sequencing reveals a mutation in PDHA1 in Leigh syndrome: A case of a Chinese boy with lethal neuropathy

Background

Leigh syndrome, the most common mitochondrial syndrome in pediatrics, has diverse clinical manifestations and is genetically heterogeneous. Pathogenic mutations in more than 75 genes of two genomes (mitochondrial and nuclear) have been identified. PDHA1 encoding the E1 alpha subunit is an X‐chromosome gene whose mutations cause pyruvate dehydrogenase complex deficiency.

Methods

Here, we have described a 12‐year‐old boy with lethal neuropathy who almost died of a sudden loss of breathing and successive cardiac arrest. Extracorporeal membrane oxygenation rescued his life. His diagnosis was corrected from Guillain–Barré syndrome to Leigh syndrome 1 month later by clinical exome sequencing. Furthermore, we used software to predict the protein structure caused by frameshift mutations. We treated the boy with vitamin B1, coenzyme Q10, and a ketogenic diet.

Results

A PDHA1 mutation (NM_000284.4:c.1167_1170del) was identified as the underlying cause. The amino acid mutation was p.Ser390LysfsTer33. Moreover, the protein structure prediction results suggested that the protein structure has changed. The parents of the child were negative, so the mutation was de novo. The comprehensive assessment of the mutation was pathogenic. His condition gradually improved after receiving treatment.

Conclusion

This case suggests that gene detection should be popularized to improve diagnosis accuracy, especially in developing countries such as China.

The mitochondrial epilepsies

Mitochondria are vital organelles within cells that undertake many important metabolic roles, the most significant of which is to generate energy to support organ function. Dysfunction of the mitochondrion can lead to a wide range of clinical features, predominantly affecting organs with a high metabolic demand such as the brain. One of the main neurological manifestations of mitochondrial disease is metabolic epilepsies. These epileptic seizures are more frequently of posterior quadrant and occipital lobe onset, more likely to present with non-convulsive status epilepticus which may last months and be more resistant to treatment from the onset. The onset of can be of any age. Childhood onset epilepsy is a major phenotypic feature in mitochondrial disorders such as Alpers-Huttenlocher syndrome, pyruvate dehydrogenase complex deficiencies, and Leigh syndrome. Meanwhile, adults with classical mitochondrial disease syndrome such as MELAS, MERFF or POLG-related disorders could present with either focal or generalised seizures. There are no specific curative treatments for mitochondrial epilepsy. Generally, the epileptic seizures should be managed by specialist neurologist with appropriate use of anticonvulsants. As a general rule, especially in disorders associated with mutation in POLG, sodium valproate is best avoided because hepato-toxicity can be fulminant and fatal.

Leigh syndrome caused by mitochondrial DNA-maintenance defects revealed by whole exome sequencing

Leigh syndrome represents a complex inherited neurometabolic and neurodegenerative disorder associated with different clinical, genetic and neuroimaging findings in the context of bilateral symmetrical lesions involving the brainstem and basal ganglia. Heterogeneous neurological manifestations such as spasticity, cerebellar ataxia, dystonia, choreoathetosis and parkinsonism are associated with multisystemic and ophthalmological abnormalities due to >75 different monogenic causes. Here, we describe the clinical and genetic features of a Brazilian cohort of patients with Leigh Syndrome in which muscle biopsy analysis showed mitochondrial DNA defects and determine the utility of whole exome sequencing for a final genetic diagnostic in this cohort.

Retrospective assessment of the most common mitochondrial DNA mutations in a large Hungarian cohort of suspect mitochondrial cases

Prevalence estimations for mitochondrial disorders still vary widely and only few epidemiologic studies have been carried out so far. With the present work we aim to give a comprehensive overview about frequencies of the most common mitochondrial mutations in Hungarian patients. A total of 1328 patients were tested between 1999 and 2012. Among them, 882 were screened for the m.3243A > G, m.8344A > G, m.8993T > C/G mutations and deletions, 446 for LHON primary mutations. The mutation frequency in our cohort was 2.61% for the m.3243A > G, 1.47% for the m.8344A > G, 17.94% for Leber's Hereditary Optic Neuropathy (m.3460G > A, m.11778G > A, m.14484T > C) and 0.45% for the m.8993T > C/G substitutions. Single mtDNA deletions were detected in 14.97%, while multiple deletions in 6.01% of the cases. The mutation frequency in Hungarian patients suggestive of mitochondrial disease was similar to other Caucasian populations. Further retrospective studies of different populations are needed in order to accurately assess the importance of mitochondrial diseases and manage these patients.

Early spinal cord and brainstem involvement in infantile Leigh syndrome possibly caused by a novel variant

Leigh syndrome, due to a dysfunction of mitochondrial energy metabolism, is a genetically heterogeneous and progressive neurologic disorder that usually occurs in infancy and childhood. Its clinical presentation and neuroimaging findings can be variable, especially early in the course of the disease. This report presents a patient with infantile Leigh syndrome who had atypical radiologic findings on serial neuroimaging studies with early and severe involvement of the cervical spinal cord and brainstem and injury to the thalami and basal ganglia occurring only late in the clinical course. Postmortem microscopic examination supported this timing of injury within the central nervous system. In addition, mitochondrial deoxyribonucleic acid sequencing showed a novel homoplasmic variant that could be responsible for this unique lethal form of Leigh syndrome.

Mitochondrial respiratory chain enzyme assay and DNA analysis in peripheral blood leukocytes for the etiological study of Chinese children with Leigh syndrome due to complex I deficiency

Mitochondrial respiratory chain complex I enzyme deficiency is the most commonly seen mitochondrial respiratory chain disorder. Although screening and diagnostic methods are available overseas, clinically feasible diagnostic methods have not yet been established in China. In this study, four Chinese boys with Leigh syndrome due to complex I deficiency were diagnosed by mitochondrial respiratory chain enzyme assay and DNA analysis using peripheral blood leukocytes. Four patients were admitted at the age of 5-14 years because of unexplained progressive neuromuscular symptoms, including motor developmental delay or regression, weakness, and seizures. Their cranial magnetic resonance imaging revealed typical finding as Leigh syndrome. Peripheral leukocyte mitochondrial respiratory chain complex I activities were found decreased to 9.6-33.1 nmol/min/mg mitochondrial protein(control 44.0 ± 5.4 nmol/min/mg). The ratios of complex I to citrate synthase activity were also decreased (8.9-19.8% in patients vs. control 48 ± 11%). Three mtDNA mutations were identified from three out of four patients, supporting the diagnosis of complex I deficiency. Point mutations m.10191T>C in mitochondrial ND3 gene, m.13513G>A in ND5 gene and m.14,453G>A in ND6 gene were detected in three patients.

Fatal breathing dysfunction in a mouse model of Leigh syndrome

Leigh syndrome (LS) is a subacute necrotizing encephalomyelopathy with gliosis in several brain regions that usually results in infantile death. Loss of murine Ndufs4, which encodes NADH dehydrogenase (ubiquinone) iron-sulfur protein 4, results in compromised activity of mitochondrial complex I as well as progressive neurodegenerative and behavioral changes that resemble LS. Here, we report the development of breathing abnormalities in a murine model of LS. Magnetic resonance imaging revealed hyperintense bilateral lesions in the dorsal brain stem vestibular nucleus (VN) and cerebellum of severely affected mice. The mutant mice manifested a progressive increase in apnea and had aberrant responses to hypoxia. Electrophysiological recordings within the ventral brain stem pre-Bötzinger respiratory complex were also abnormal. Selective inactivation of Ndufs4 in the VN, one of the principle sites of gliosis, also led to breathing abnormalities and premature death. Conversely, Ndufs4 restoration in the VN corrected breathing deficits and prolonged the life span of knockout mice. These data demonstrate that mitochondrial dysfunction within the VN results in aberrant regulation of respiration and contributes to the lethality of Ndufs4-knockout mice.

Mitochondrial disease and epilepsy

Mitochondrial respiratory chain disorders are relatively common inborn errors of energy metabolism, with a combined prevalence of one in 5000. These disorders typically affect tissues with high energy requirements, and cerebral involvement occurs frequently in childhood, often manifesting in seizures. Mitochondrial diseases are genetically heterogeneous; to date, mutations have been reported in all 37 mitochondrially encoded genes and more than 80 nuclear genes. The major genetic causes of mitochondrial epilepsy are mitochondrial DNA mutations (including those typically associated with the mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes [MELAS] and myoclonic epilepsy with ragged red fibres [MERRF] syndromes); mutations in POLG (classically associated with Alpers syndrome but also presenting as the mitochondrial recessive ataxia syndrome [MIRAS], spinocerebellar ataxia with epilepsy [SCAE], and myoclonus, epilepsy, myopathy, sensory ataxia [MEMSA] syndromes in older individuals) and other disorders of mitochondrial DNA maintenance; complex I deficiency; disorders of coenzyme Q(10) biosynthesis; and disorders of mitochondrial translation such as RARS2 mutations. It is not clear why some genetic defects, but not others, are particularly associated with seizures. Epilepsy may be the presenting feature of mitochondrial disease but is often part of a multisystem clinical presentation. Mitochondrial epilepsy may be very difficult to manage, and is often a poor prognostic feature. At present there are no curative treatments for mitochondrial disease. Individuals with mitochondrial epilepsy are frequently prescribed multiple anticonvulsants, and the role of vitamins and other nutritional supplements and the ketogenic diet remain unproven.

Analysis of the mitochondrial complex I-V enzyme activities of peripheral leukocytes in oxidative phosphorylation disorders

Mitochondrial oxidative phosphorylation defects are a common cause of mitochondrial diseases, which are characterized by multiorgan involvement and clinically heterogeneous manifestations. Diagnosis is difficult because of the lack of clinically feasible methods. In this study, mitochondrial complex I-V enzyme activity was measured in 64 patients with suspected mitochondrial disease and 200 healthy controls. Spectrophotometric assay was used for the analysis of mitochondrial complex I-V enzyme activity in peripheral leukocytes. Diagnosis was based on clinical presentation, magnetic resonance imaging (MRI), muscle pathology, and point mutation screening in mitochondrial DNA. The differential diagnosis of aminoacidopathies, organic acidurias, and fatty acid β-oxidation defects was made. Thirty-five patients (54.7%) were diagnosed with Leigh syndrome based on characteristic brain MRI. Complex enzyme activity in controls was found to be stable. A deficiency in the oxidative phosphorylation was found in 29 patients (45.3%). Twenty (31.2%) patients had isolated complex defects, complex I deficiency (n = 2, 3.1%), complex II deficiency (n = 3, 4.7%), complex III deficiency (n = 5, 7.8%), complex IV deficiency (n = 5, 7.8%), and complex V deficiency (n = 5, 7.8%). Nine patients were found to have combined deficiencies, 3 (4.7%) had combined deficiencies of complex I and IV, 2 (3.1%) had combined deficiencies of complex III and V, and 2 (3.1%) had a combined deficiency of complex I and V. In conclusion, the peripheral leukocyte oxidative phosphorylation enzyme activity assay was found to be a reliable method for the diagnosis of mitochondrial diseases.

A novel presentation of inappropriate antidiuretic hormone secretion in Leigh syndrome with the myoclonic epilepsy and ragged red fibers, mitochondrial DNA 8344A>G mutation

A 17-month-old infant presented with a 2-week history of lethargy, anorexia, and an abnormal respiratory pattern on a previous 4-month history of hypotonia and gross motor delay, suggesting a clinical phenotype of Leigh syndrome. The patient experienced no epileptic seizures. Biochemical investigations were normal other than showing evidence of inappropriate secretion of antidiuretic hormone, and cerebral magnetic resonance imaging (MRI) showed symmetrical lesions in the cervical cord and lower brain stem. Initial screening investigations for a mitochondrial cytopathy were negative. Muscle histochemistry demonstrated reduced staining of cytochrome c oxidase but no ragged red fibers. Blood and muscle-derived DNA demonstrated a high level (92% and 82%, respectively) of the m.8344A>G mutation seen in patients with the mitochondrial cytopathy, ''myoclonic epilepsy with ragged red fibers on muscle biopsy.'' This infant's early presentation including inappropriate antidiuretic secretion due to presumed renal salt loss and rapid course appears to be unique to this mutation.

Analysis of mtDNA A3243G mutation frequency in Hungary

The A3243G mutation in the mitochondrial tRNALeu (UUR) gene is one of the most common causes of mitochondrial DNA related disorders. Originally it was described in MELAS syndrome (Mitochondrial Encephalomyopathy, Lactic acidosis, Stroke-like episodes), later it had been found to be associated with various phenotypes. In our study the mutation frequency of the A3243G mtDNA mutation was investigated in patients with maternal sensoneural hearing loss, stroke-like episodes, ataxia and myopathy with undetermined etiology. We screened 631 Hungarian patients in North-East, South-West and Central Hungary between 1999 and 2008 for this mutation. The mtDNA analysis was performed from blood and/or muscle tissue. The A3243G substitution was present in 6 patients in heteroplasmic form. The segregation analysis detected 8 further cases. The frequency of the A3243G mutation was 2.22% in the investigated patients. The A3243G mutation frequency in Hungary does not differ significantly from other countries using similar patient selection criteria, however in Finland a higher mutation rate was found. In studies investigated the mutation frequency of this mutation in diabetes mellitus similarly wide variety was detected as well. We conclude that the study design has a huge impact on the result of the genetic epidemiological investigation analyzing the mutation frequency of the A3243G mutation due to the broad clinical phenotype and the different mutation load in different tissues.

SURF1 missense mutations promote a mild Leigh phenotype

SURF1 gene mutations are the most common cause of Leigh syndrome (LS), a rare progressive neurodegenerative disorder of infancy, characterized by symmetric necrotizing lesions and hypervascularity in the brainstem and basal ganglia, leading to death before the age of 4 years. Most of the reported mutations create premature termination codons, whereas missense mutations are rare. The aim of the study was to characterize the natural history of LS patients carrying at least one missense mutation in the SURF1 gene. Nineteen such patients (8 own cases and 11 reported in the literature) were compared with a reference group of 20 own c.845_846delCT homozygous patients, and with other LS(SURF-) cases described in the literature. Disease onset in the studied group was delayed. Acute failure to thrive and hyperventilation episodes were rare, respiratory failure did not appear before the age of 4 years. Dystonia, motor regression and eye movement dissociation developed slowly. The number of patients who survived 7 years of life totaled 9 out of 15 (60%) in the 'missense group' and 1 out of 26 (4%) patients with mutations leading to truncated proteins.

IN CONCLUSION

(i) The presence of a missense mutation in the SURF1 gene may correlate with a milder course and longer survival of Leigh patients, (ii) normal magnetic resonance imaging (MRI) findings, normal blood lactate value, and only mild decrease of cytochrome c oxidase (COX) activity are not sufficient reasons to forego SURF1 mutation analysis in differential diagnosis.

SURF-1 gene mutation associated with leukoencephalopathy in a 2-year-old

Mutations in the nuclear SURF-1 gene lead directly to cytochrome-c oxidase deficiency, the most common respiratory chain defect in Leigh syndrome, a neurodegenerative mitochondrial disease involving the deep gray matter and brain stem. We describe the second documented case in the literature to have a SURF-1 mutation presenting with diffuse leukodystrophy, adding to the growing number of cases of mitochondrial syndromes presenting with white matter disease. We examine magnetic resonance imaging (MRI) findings, which suggest that high-grade cytotoxic edema on diffusion-weighted imaging may be a helpful diagnostic feature in differentiating mitochondrial leukodystrophy from other, more common leukodystrophies. We show how MRI white matter findings may progress to include the brain stem, suggesting that a leukodystrophy due to respiratory chain defects can precede more classic Leigh syndrome deep gray matter radiographic findings.

Advances in molecular diagnostics for mitochondrial diseases

BACKGROUND

Mitochondrial disorders (MD) are diseases caused by impairment of the mitochondrial respiratory chain. Phenotypes are polymorphous and may range from pure myopathy to multisystemic disorders. The genetic defect can be located on mitochondrial or nuclear DNA. At present, diagnosis of MD requires a complex approach: measurement of serum lactate, electromyography, muscle histology and enzymology, and genetic analysis. Magnetic resonance spectroscopy allows the assessment of tissue metabolic alterations, thus providing useful information for the diagnosis and monitoring of MD. Molecular soluble markers of mitochondrial dysfunction, at rest and during exercise, can identify the impairment of the aerobic system in MD, but a reliable biomarker for the screening or diagnosis of MD is still needed.

OBJECTIVE

Molecular and genetic characterization of MD, together with other experimental approaches, contribute to add new insights to these diseases. Here, the role and advances of diagnostic techniques for MD are reviewed.

CONCLUSION

Possible applications of the results obtained by new molecular investigative approaches could in future guide therapeutic strategies.

High prevalence of SURF1 c.845_846delCT mutation in Polish Leigh patients

Leigh syndrome is a neuropathological disorder with typical morphological changes in brain, appearing regardless of diverse molecular background. One of the most common enzymatic defects in Leigh patients is cytochrome c oxidase deficiency associated with recessive mutations in the SURF1 gene. To assess the SURF1 mutation profile among Polish patients we studied 41 affected children from 34 unrelated families by PCR-SSCP and sequencing. Four novel mutations, c.39delG, c.752-1G>C, c.800_801insT, c.821A>G, and five described pathogenic changes, c.311_312insAT312_321del10, c.688C>T, c.704T>C, c.756_757delCA, c.845_846delCT, were identified in 85.3% of analysed probands. One mutation, c.845_846delCT, was identified in 77.6% of SURF1 alleles. Up to now, it has been reported only in 9% of alleles in other parts of the world. The deletion was used as LS(SURF1-) marker in population studies. Eight heterozygous carriers of the mutation were found in a cohort of 2890 samples. The estimated c.845_846delCT allele frequency is 1:357 (0.28+/-0.2%), and the lowest predicted LS(SURF1-) frequency in Poland 1:126,736.births. Relatively high frequency of LS(SURF1-) in Poland with remarkable c.845_846delCT mutation dominance allows one to start the differential diagnosis of LS in each patient of Polish (and probably Slavonic) origin from the direct search for c.845_846delCT SURF1 mutation.

Approaches to finding the molecular basis of mitochondrial oxidative phosphorylation disorders

Inherited disorders of mitochondrial oxidative phosphorylation are the most common group of inborn errors of metabolism and cause a wide range of clinical presentations. Mitochondrial DNA encodes 13 protein subunits required for oxidative phosphorylation plus 22 transfer RNAs and two ribosomal RNAs, and mutations in most of these genes cause human disease. Nuclear genes encode most of the protein subunits and all other proteins required for mitochondrial biogenesis and mitochondrial DNA replication and expression. Mutations in 64 nuclear genes and 34 mitochondrial genes are now known to cause mitochondrial disease and many novel mitochondrial disease genes await discovery. The genetic complexity of oxidative phosphorylation means that maternal, autosomal recessive, autosomal dominant and X-linked modes of inheritance can occur, along with de novo mutations. This complexity presents a challenge in planning efficient molecular genetic diagnosis of patients with suspected mitochondrial disease. In some situations, clinical phenotype can be strongly predictive of the underlying genotype. However, more often this is not the case and it is usually helpful, particularly with pediatric patients, to determine whether the activity of one or more of the individual oxidative phosphorylation enzymes is deficient before proceeding with mutation analysis. In this review we will summarize the genetic bases of mitochondrial disease and discuss some approaches to integrate information from clinical presentation, laboratory findings, family history, and imaging to guide molecular investigation.

MtDNA mutations are a common cause of severe disease phenotypes in children with Leigh syndrome

Leigh syndrome is a common clinical manifestation in children with mitochondrial disease and other types of inborn errors of metabolism. We characterised clinical symptoms, prognosis, respiratory chain function and performed extensive genetic analysis of 25 Swedish children suffering from Leigh syndrome with the aim to obtain insights into the molecular pathophysiology and to provide a rationale for genetic counselling. We reviewed the clinical history of all patients and used muscle biopsies in order to perform molecular, biochemical and genetic investigations, including sequencing the entire mitochondrial DNA (mtDNA), the mitochondrial DNA polymerase (POLGA) gene and the surfeit locus protein 1 (SURF1) gene. Respiratory chain enzyme activity measurements identified five patients with isolated complex I deficiency and five with combined enzyme deficiencies. No patient presented with isolated complex IV deficiency. Seven patients had a decreased ATP production rate. Extensive sequence analysis identified eight patients with pathogenic mtDNA mutations and one patient with mutations in POLGA. Mutations of mtDNA are a common cause of LS and mtDNA analysis should always be included in the diagnosis of LS patients, whereas SURF1 mutations are not a common cause of LS in Sweden. Unexpectedly, age of onset, clinical symptoms and prognosis did not reveal any clear differences in LS patients with mtDNA or nuclear DNA mutations.

Leigh and Leigh-like syndrome in children and adults

Leigh syndrome (also termed subacute, necrotizing encephalopathy) is a devastating neurodegenerative disorder, characterized by almost identical brain changes, e.g., focal, bilaterally symmetric lesions, particularly in the basal ganglia, thalamus, and brainstem, but with considerable clinical and genetic heterogeneity. Clinically, Leigh syndrome is characterized by a wide variety of abnormalities, from severe neurologic problems to a near absence of abnormalities. Most frequently the central nervous system is affected, with psychomotor retardation, seizures, nystagmus, ophthalmoparesis, optic atrophy, ataxia, dystonia, or respiratory failure. Some patients also present with peripheral nervous system involvement, including polyneuropathy or myopathy, or non-neurologic abnormalities, e.g., diabetes, short stature, hypertrichosis, cardiomyopathy, anemia, renal failure, vomiting, or diarrhea (Leigh-like syndrome). In the majority of cases, onset is in early childhood, but in a small number of cases, adults are affected. In the majority of cases, dysfunction of the respiratory chain (particularly complexes I, II, IV, or V), of coenzyme Q, or of the pyruvate dehydrogenase complex are responsible for the disease. Associated mutations affect genes of the mitochondrial or nuclear genome. Leigh syndrome and Leigh-like syndrome are the mitochondrial disorders with the largest genetic heterogeneity.