Management of seizures in patients with primary mitochondrial diseases: consensus statement from the InterERNs Mitochondrial Working Group

BACKGROUND AND PURPOSE

Primary mitochondrial diseases (PMDs) are common inborn errors of energy metabolism, with an estimated prevalence of one in 4300. These disorders typically affect tissues with high energy requirements, including heart, muscle and brain. Epilepsy may be the presenting feature of PMD, can be difficult to treat and often represents a poor prognostic feature. The aim of this study was to develop guidelines and consensus recommendations on safe medication use and seizure management in mitochondrial epilepsy.

METHODS

A panel of 24 experts in mitochondrial medicine, pharmacology and epilepsy management of adults and/or children and two patient representatives from seven countries was established. Experts were members of five different European Reference Networks, known as the Mito InterERN Working Group. A Delphi technique was used to allow the panellists to consider draft recommendations on safe medication use and seizure management in mitochondrial epilepsy, using two rounds with predetermined levels of agreement.

RESULTS

A high level of consensus was reached regarding the safety of 14 out of all 25 drugs reviewed, resulting in endorsement of National Institute for Health and Care Excellence guidelines for seizure management, with some modifications. Exceptions including valproic acid in POLG disease, vigabatrin in patients with γ-aminobutyric acid transaminase deficiency and topiramate in patients at risk for renal tubular acidosis were highlighted.

CONCLUSIONS

These consensus recommendations describe our intent to improve seizure control and reduce the risk of drug-related adverse events in individuals living with PMD-related epilepsy.

Phenotypic spectrum and clinical course of single large-scale mitochondrial DNA deletion disease in the paediatric population: a multicentre study

BACKGROUND

Large-scale mitochondrial DNA deletions (LMD) are a common genetic cause of mitochondrial disease and give rise to a wide range of clinical features. Lack of longitudinal data means the natural history remains unclear. This study was undertaken to describe the clinical spectrum in a large cohort of patients with paediatric disease onset.

METHODS

A retrospective multicentre study was performed in patients with clinical onset <16 years of age, diagnosed and followed in seven European mitochondrial disease centres.

RESULTS

A total of 80 patients were included. The average age at disease onset and at last examination was 10 and 31 years, respectively. The median time from disease onset to death was 11.5 years. Pearson syndrome was present in 21%, Kearns-Sayre syndrome spectrum disorder in 50% and progressive external ophthalmoplegia in 29% of patients. Haematological abnormalities were the hallmark of the disease in preschool children, while the most common presentations in older patients were ptosis and external ophthalmoplegia. Skeletal muscle involvement was found in 65% and exercise intolerance in 25% of the patients. Central nervous system involvement was frequent, with variable presence of ataxia (40%), cognitive involvement (36%) and stroke-like episodes (9%). Other common features were pigmentary retinopathy (46%), short stature (42%), hearing impairment (39%), cardiac disease (39%), diabetes mellitus (25%) and renal disease (19%).

CONCLUSION

Our study provides new insights into the phenotypic spectrum of childhood-onset, LMD-associated syndromes. We found a wider spectrum of more prevalent multisystem involvement compared with previous studies, most likely related to a longer time of follow-up.

Renal Phenotype in Mitochondrial Diseases: A Multicenter Study

AIMS

This study aimed to investigate associations between renal and extrarenal manifestations of mitochondrial diseases and their natural history as well as predictors of renal disease severity and overall disease outcome. The secondary aim was to generate a protocol of presymptomatic assessment and monitoring of renal function in patients with a defined mitochondrial disease.

METHODS

A multicenter, retrospective cohort study was performed by the Mitochondrial Clinical and Research Network (MCRN). Patients of any age with renal manifestations associated with a genetically verified mitochondrial disease were included from 8 expert European centers specializing in mitochondrial diseases: Gothenburg, Oulu, Copenhagen, Bergen, Helsinki, Stockholm, Rotterdam, and Barcelona.

RESULTS

Of the 36 patients included, two-thirds had mitochondrial DNA-associated disease. Renal manifestations were the first sign of mitochondrial disease in 19%, and renal involvement was first identified by laboratory tests in 57% of patients. Acute kidney injury occurred in 19% of patients and was the first sign of renal disease in the majority of these. The most common renal manifestation was chronic kidney disease (75% with stage 2 or greater), followed by tubulopathy (44.4%), the latter seen mostly among patients with single large-scale mitochondrial DNA deletions. Acute kidney injury and tubulopathy correlated with worse survival outcome. The most common findings on renal imaging were increased echogenicity and renal dysplasia/hypoplasia. Renal histology revealed focal segmental glomerulosclerosis, nephrocalcinosis, and nephronophthisis.

CONCLUSION

Acute kidney injury is a distinct renal phenotype in patients with mitochondrial disease. Our results highlight the importance to recognize renal disease as a sign of an underlying mitochondrial disease. Acute kidney injury and tubulopathy are 2 distinct indicators of poor survival in patients with mitochondrial diseases.

Expanding the phenotypic spectrum of BCS1L-related mitochondrial disease

Objective

To delineate the full phenotypic spectrum of BCS1L‐related disease, provide better understanding of the genotype–phenotype correlations and identify reliable prognostic disease markers.

Methods

We performed a retrospective multinational cohort study of previously unpublished patients followed in 15 centres from 10 countries. Patients with confirmed biallelic pathogenic BCS1L variants were considered eligible. Clinical, laboratory, neuroimaging and genetic data were analysed. Patients were stratified into different groups based on the age of disease onset, whether homozygous or compound heterozygous for the c.232A>G (p.Ser78Gly) variant, and those with other pathogenic BCS1L variants.

Results

Thirty‐three patients were included. We found that growth failure, lactic acidosis, tubulopathy, hepatopathy and early death were more frequent in those with disease onset within the first month of life. In those with onset after 1 month, neurological features including movement disorders and seizures were more frequent. Novel phenotypes, particularly involving movement disorder, were identified in this group. The presence of the c.232A>G (p.Ser78Gly) variant was associated with significantly worse survival and exclusively found in those with disease onset within the first month of life, whilst other pathogenic BCS1L variants were more frequent in those with later symptom onset.

Interpretation

The phenotypic spectrum of BCS1L‐related disease comprises a continuum of clinical features rather than a set of separate syndromic clinical identities. Age of onset defines BCS1L‐related disease clinically and early presentation is associated with poor prognosis. Genotype correlates with phenotype in the presence of the c.232A>G (p.Ser78Gly) variant.

Diagnostic value of serum biomarkers FGF21 and GDF15 compared to muscle sample in mitochondrial disease

The aim of this study was to compare the value of serum biomarkers, fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15), with histological analysis of muscle in the diagnosis of mitochondrial disease. We collected 194 serum samples from patients with a suspected or known mitochondrial disease. Biomarkers were analyzed blinded using enzyme-labeled immunosorbent assay. Clinical data were collected using a structured questionnaire. Only 39% of patients with genetically verified mitochondrial disease had mitochondrial pathology in their muscle histology. In contrast, biomarkers were elevated in 62% of patients with genetically verified mitochondrial disease. Those with both biomarkers elevated had a muscle manifesting disorder and a defect affecting mitochondrial DNA expression. If at least one of the biomarkers was induced and the patient had a myopathic disease, a mitochondrial DNA expression disease was the cause with 94% probability. Among patients with biomarker analysis and muscle biopsy taken <12 months apart, a mitochondrial disorder would have been identified in 70% with analysis of FGF21 and GDF15 compared to 50% of patients whom could have been identified with muscle biopsy alone. Muscle findings were nondiagnostic in 72% (children) and 45% (adults). Induction of FGF21 and GDF15 suggest a mitochondrial etiology as an underlying cause of a muscle manifesting disease. Normal biomarker values do not, however, rule out a mitochondrial disorder, especially if the disease does not manifest in muscle. We suggest that FGF21 and GDF15 together should be first-line diagnostic investigations in mitochondrial disease complementing muscle biopsy.

Serum biomarkers in primary mitochondrial disorders

The aim of this study was to explore the utility of the serum biomarkers neurofilament light chain, fibroblast growth factor 21 and growth and differentiation factor 15 in diagnosing primary mitochondrial disorders. We measured serum neurofilament light chain, fibroblast growth factor 21 and growth and differentiation factor 15 in 26 patients with a genetically proven mitochondrial disease. Fibroblast growth factor 21 and growth and differentiation factor 15 were measured by enzyme-linked immunosorbent assay and neurofilament light chain with the Simoa assay. Neurofilament light chain was highest in patients with multi-systemic involvement that included the central nervous system such as those with the m.3242A>G mutation. Mean neurofilament light chain was also highest in patients with epilepsy versus those without [49.74 pg/ml versus 19.7 pg/ml (P = 0.015)], whereas fibroblast growth factor 21 and growth and differentiation factor 15 levels were highest in patients with prominent myopathy, such as those with single-mitochondrial DNA deletion. Our results suggest that the combination of neurofilament light chain, fibroblast growth factor 21 and growth and differentiation factor 15 is useful in the diagnostic evaluation of mitochondrial disease. Growth and differentiation factor 15 and fibroblast growth factor 21 identify those with muscle involvement, whereas neurofilament light chain is a clear marker for central nervous system involvement independent of underlying mitochondrial pathology. Levels of neurofilament light chain appear to correlate with the degree of ongoing damage suggesting, therefore, that monitoring neurofilament light chain levels may provide prognostic information and a way of monitoring disease activity.

The impact of gender, puberty, and pregnancy in patients with POLG disease

Objective

To study the impact of gender, puberty, and pregnancy on the expression of POLG disease, one of the most common mitochondrial diseases known.

Methods

Clinical, laboratory, and genetic data were collected retrospectively from 155 patients with genetically confirmed POLG disease recruited from seven European countries. We used the available data to study the impact of gender, puberty, and pregnancy on disease onset and deterioration.

Results

We found that disease onset early in life was common in both sexes but there was also a second peak in females around the time of puberty. Further, pregnancy had a negative impact with 10 of 14 women (71%) experiencing disease onset or deterioration during pregnancy.

Interpretation

Gender clearly influences the expression of POLG disease. While onset very early in life was common in both males and females, puberty in females appeared associated both with disease onset and increased disease activity. Further, both disease onset and deterioration, including seizure aggravation and status epilepticus, appeared to be associated with pregnancy. Thus, whereas disease activity appears maximal early in life with no subsequent peaks in males, both menarche and pregnancy appear associated with disease onset or worsening in females. This suggests that hormonal changes may be a modulating factor.

Simplifying the clinical classification of polymerase gamma (POLG) disease based on age of onset; studies using a cohort of 155 cases

BACKGROUND

Variants in POLG are one of the most common causes of inherited mitochondrial disease. Phenotypic classification of POLG disease has evolved haphazardly making it complicated and difficult to implement in everyday clinical practise. The aim of our study was to simplify the classification and facilitate better clinical recognition.

METHODS

A multinational, retrospective study using data from 155 patients with POLG variants recruited from seven European countries.

RESULTS

We describe the spectrum of clinical features associated with POLG variants in the largest known cohort of patients. While clinical features clearly form a continuum, stratifying patients simply according to age of onset-onset prior to age 12 years; onset between 12 and 40 years and onset after the age of 40 years, permitted us to identify clear phenotypic and prognostic differences. Prior to 12 years of age, liver involvement (87%), seizures (84%), and feeding difficulties (84%) were the major features. For those with onset between 12 and 40 years, ataxia (90%), peripheral neuropathy (84%), and seizures (71%) predominated, while for those with onset over 40 years, ptosis (95%), progressive external ophthalmoplegia (89%), and ataxia (58%) were the major clinical features. The earlier the onset the worse the prognosis. Patients with epilepsy and those with compound heterozygous variants carried significantly worse prognosis.

CONCLUSION

Based on our data, we propose a simplified POLG disease classification, which can be used to guide diagnostic investigations and predict disease course.

Polymerase gamma-related mitochondrial disorder

DNA Polymerase gamma (POLG) is an enzyme that replicates and repairs mitochondrial DNA. Mutations in the gene that codes for the catalytic subunit of the enzyme, the POLG gene, are one of the most common causes of mitochondrial disease. POLG-related disorders can have overlapping phenotypes and affect a number of organ systems, and first onset may occur at any age. The disease group can serve as a paradigm for understanding mitochondrial diseases in general.

Progressive deafness-dystonia due to SERAC1 mutations: A study of 67 cases

OBJECTIVE

3-Methylglutaconic aciduria, dystonia-deafness, hepatopathy, encephalopathy, Leigh-like syndrome (MEGDHEL) syndrome is caused by biallelic variants in SERAC1.

METHODS

This multicenter study addressed the course of disease for each organ system. Metabolic, neuroradiological, and genetic findings are reported.

RESULTS

Sixty-seven individuals (39 previously unreported) from 59 families were included (age range = 5 days-33.4 years, median age = 9 years). A total of 41 different SERAC1 variants were identified, including 20 that have not been reported before. With the exception of 2 families with a milder phenotype, all affected individuals showed a strikingly homogeneous phenotype and time course. Severe, reversible neonatal liver dysfunction and hypoglycemia were seen in >40% of all cases. Starting at a median age of 6 months, muscular hypotonia (91%) was seen, followed by progressive spasticity (82%, median onset = 15 months) and dystonia (82%, 18 months). The majority of affected individuals never learned to walk (68%). Seventy-nine percent suffered hearing loss, 58% never learned to speak, and nearly all had significant intellectual disability (88%). Magnetic resonance imaging features were accordingly homogenous, with bilateral basal ganglia involvement (98%); the characteristic "putaminal eye" was seen in 53%. The urinary marker 3-methylglutaconic aciduria was present in virtually all patients (98%). Supportive treatment focused on spasticity and drooling, and was effective in the individuals treated; hearing aids or cochlear implants did not improve communication skills.

INTERPRETATION

MEGDHEL syndrome is a progressive deafness-dystonia syndrome with frequent and reversible neonatal liver involvement and a strikingly homogenous course of disease. Ann Neurol 2017;82:1004-1015.

The presence of anaemia negatively influences survival in patients with POLG disease

BACKGROUND

Mitochondria play an important role in iron metabolism and haematopoietic cell homeostasis. Recent studies in mice showed that a mutation in the catalytic subunit of polymerase gamma (POLG) was associated with haematopoietic dysfunction including anaemia. The aim of this study was to analyse the frequency of anaemia in a large cohort of patients with POLG related disease.

METHODS

We conducted a multi-national, retrospective study of 61 patients with confirmed, pathogenic biallelic POLG mutations from six centres, four in Norway and two in the United Kingdom. Clinical, laboratory and genetic data were collected using a structured questionnaire. Anaemia was defined as an abnormally low haemoglobin value adjusted for age and sex. Univariate survival analysis was performed using log-rank test to compare differences in survival time between categories.

RESULTS

Anaemia occurred in 67% (41/61) of patients and in 23% (14/61) it was already present at clinical presentation. The frequency of anaemia in patients with early onset disease including Alpers syndrome and myocerebrohepatopathy spectrum (MCHS) was high (72%) and 35% (8/23) of these had anaemia at presentation. Survival analysis showed that the presence of anaemia was associated with a significantly worse survival (P = 0.004).

CONCLUSION

Our study reveals that anaemia can be a feature of POLG-related disease. Further, we show that its presence is associated with significantly worse prognosis either because anaemia itself is impacting survival or because it reflects the presence of more serious disease. In either case, our data suggests anaemia is a marker for negative prognosis.

Understanding the Epilepsy in POLG Related Disease

Epilepsy is common in polymerase gamma (POLG) related disease and is associated with high morbidity and mortality. Epileptiform discharges typically affect the occipital regions initially and focal seizures, commonly evolving to bilateral convulsive seizures which are the most common seizure types in both adults and children. Our work has shown that mtDNA depletion—i.e., the quantitative loss of mtDNA—in neurones is the earliest and most important factor of the subsequent development of cellular dysfunction. Loss of mtDNA leads to loss of mitochondrial respiratory chain (MRC) components that, in turn, progressively disables energy metabolism. This critically balanced neuronal energy metabolism leads to both a chronic and continuous attrition (i.e., neurodegeneration) and it leaves the neurone unable to cope with increased demand that can trigger a potentially catastrophic cycle that results in acute focal necrosis. We believe that it is the onset of epilepsy that triggers the cascade of damage. These events can be identified in the stepwise evolution that characterizes the clinical, Electroencephalography (EEG), neuro-imaging, and neuropathology findings. Early recognition with prompt and aggressive seizure management is vital and may play a role in modifying the epileptogenic process and improving survival.

CFS in Children and Adolescent: Ten Years of Retrospective Clinical Evaluation

Aim. To estimate number of children being diagnosed with chronic fatigue syndrome (CFS). Methods. For a period of 10 years (2002-2011) data from children being referred for fatigue symptoms were collected retrospectively. Results. Thirty-seven children were referred. Four were excluded due to incorrect coding. Six (18%) patients received other diagnoses at the end of evaluation time. Of the 27 who received the diagnosis G93.3, four had a previous chronic illness, while 23 patients were previously healthy. All patients reported onset of fatigue symptom in relation to an infection, and all tested positive for IgG to either Epstein-Barr virus, cytomegalovirus or borrelia, indicating previous infection. There were 16 (59%) boys among the 27 patients. The mean age at the debut of fatigue symptoms was 141 months (SD 30) for boys and 136 months (SD 31) for girls, respectively. Being underweight, defined as BMI < 17.5, was found in 12 (44%) patients. Conclusion. An increasing number of children and adolescents are evaluated for CFS. The clinical assessment of children and adolescents with possible CFS need systematically evaluation. Nutritional status, possible eating disorder, and psychosocial issues need to be addressed and evaluated carefully. A multidisciplinary approach is essential when assessing CFS in children and adolescents. There is a need for European guidelines.