Kalliopi Sofou

Whole exome sequencing reveals mutations in NARS2 and PARS2, encoding the mitochondrial asparaginyl-tRNA synthetase and prolyl-tRNA synthetase, in patients with Alpers syndrome.

Alpers syndrome is a progressive neurodegenerative disorder that presents in infancy or early childhood and is characterized by diffuse degeneration of cerebral gray matter. While mutations in POLG1, the gene encoding the gamma subunit of the mitochondrial DNA polymerase, have been associated with Alpers syndrome with liver failure (Alpers–Huttenlocher syndrome), the genetic cause of Alpers syndrome in most patients remains unidentified. With whole exome sequencing we have identified mutations in NARS2 and PARS2, the genes encoding the mitochondrial asparaginyl‐ and prolyl‐tRNA synthetases, in two patients with Alpers syndrome. One of the patients was homozygous for a missense mutation (c.641C>T, p.P214L) in NARS2. The affected residue is predicted to be located in the stem of a loop that participates in dimer interaction. The other patient was compound heterozygous for a one base insertion (c.1130dupC, p.K378 fs*1) that creates a premature stop codon and a missense mutation (c.836C>T, p.S279L) located in a conserved motif of unknown function in PARS2. This report links for the first time mutations in these genes to human disease in general and to Alpers syndrome in particular.

MRI of the brain in childhood-onset mitochondrial disorders with central nervous system involvement

We retrospectively studied the brain MRIs of 66 pediatric patients with mitochondrial disorder with central nervous system involvement. Forty-one patients had an identified genetic etiology. A predominance of cerebrocortical lesions was mainly seen in patients with MELAS and Alpers syndrome. Basal ganglia were predominantly affected in patients with Leigh syndrome. All patients with leukoencephalopathy had pathological spectroscopy. Cerebrocortical atrophy with agenesis/atrophy of the corpus callosum was seen in patients with congenital lactic acidosis with or without pyruvate dehydrogenase complex deficiency. The diagnostic approach used in our study--from the neuroanatomical/neurofunctional lesion to disease identification--assists the physician in the use of brain neuroimaging early in the diagnostic work-up of suspected mitochondrial disorders.

Phenotypic and genotypic variability in Alpers syndrome.

BACKGROUND Alpers syndrome is one of the most common phenotypes of mitochondrial disorders in early childhood and has been associated with pathogenic mutations in POLG1. AIMS To investigate the phenotypic-genotypic correlations in Alpers syndrome and to identify potential differences among patients with Alpers syndrome with or without pathogenic POLG1 mutations. METHODS Patients with the phenotype of Alpers syndrome who were referred to our pediatric hospital during 1984-2007 and were diagnosed with mitochondrial encephalomyopathy underwent further biochemical, morphological and genetic investigations. RESULTS A total of 19 patients were included in the study, of whom six had pathogenic POLG1 mutations including a novel mutation (c.907 G>A, p.Gly303Arg). Complete mtDNA sequencing in the subgroup without POLG1 mutations showed 5 novel and 5 very rare mtDNA variants considered as rare polymorphisms. Compared to POLG1(-) patients, the POLG1(+) patients more frequently had seizures at onset, which often became refractory. Ataxia and stroke-like episodes were much more common, while microcephaly and spasticity were encountered almost solely in the POLG1(-) group. Hepatic and ophthalmological involvement developed in 79% and 88% of patients, respectively. Most of the patients in both groups had predominant deficiency of complex I. In addition to the major degenerative changes in the cerebral cortex, the basal ganglia, thalamus and white matter were also involved to variable extent. CONCLUSION Alpers syndrome is a heterogeneous syndrome that should be considered in patients with early-onset progressive cortical encephalopathy regardless of liver involvement. The phenotype is different depending on the presence or absence of POLG1 mutations.

Mitochondrial Disease A Challenge for the Caregiver, the Family, and Society

Mitochondrial diseases represent a genetically and clinically heterogeneous group of inherited metabolic disorders, often resulting in poor functional and survival outcomes for the patient and considerable psychosocial distress for the caregiver. The systematic review undertaken in the present paper emphasizes the critical role of the caregiver in the management of a child with mitochondrial disease, with focus on the burden of mitochondrial disease on the caregiver, the family, and society.

Broad phenotypic variability in patients with complex I deficiency due to mutations in NDUFS1 and NDUFV1.

We report clinical, metabolic, genetic and neuroradiological findings in five patients from three different families with isolated complex I deficiency. Genetic analysis revealed mutations in NDUFS1 in three patients and in NDUFV1 in two patients. Four of the mutations are novel and affect amino acid residues that either are invariant among species or conserved in their properties. The presented clinical courses are characterized by leukoencephalopathy or early death and expand the already heterogeneous phenotypic spectrum. A literature review was performed, showing that patients with mutations in NDUFS1 in general have a worse prognosis than patients with mutations in NDUFV1.

Phenotype-genotype correlations in Leigh syndrome: new insights from a multicentre study of 96 patients

Background Leigh syndrome is a phenotypically and genetically heterogeneous mitochondrial disorder. While some genetic defects are associated with well-described phenotypes, phenotype-genotype correlations in Leigh syndrome are not fully explored. Objective We aimed to identify phenotype-genotype correlations in Leigh syndrome in a large cohort of systematically evaluated patients. Methods We studied 96 patients with genetically confirmed Leigh syndrome diagnosed and followed in eight European centres specialising in mitochondrial diseases. Results We found that ataxia, ophthalmoplegia and cardiomyopathy were more prevalent among patients with mitochondrial DNA defects. Patients with mutations in MT-ND and NDUF genes with complex I deficiency shared common phenotypic features, such as early development of central nervous system disease, followed by high occurrence of cardiac and ocular manifestations. The cerebral cortex was affected in patients with NDUF mutations significantly more often than the rest of the cohort. Patients with the m.8993T>G mutation in MT-ATP6 gene had more severe clinical and radiological manifestations and poorer disease outcome compared with patients with the m.8993T>C mutation. Conclusion Our study provides new insights into phenotype-genotype correlations in Leigh syndrome and particularly in patients with complex I deficiency and with defects in the mitochondrial ATP synthase.

Ophthalmological characteristics in children with Leigh syndrome – A long‐term follow‐up

To describe ophthalmological characteristics in children with Leigh syndrome (LS), an inherited, progressive, mitochondrial encephalomyopathy, at diagnosis and over time, and relate the results to causative genetic mutations.

Cerebrospinal fluid neurofilament light is associated with survival in mitochondrial disease patients

We studied the biomarker patterns related to axonal injury, astrogliosis and amyloid metabolism in cerebrospinal fluid (CSF) of children and adolescents with mitochondrial encephalopathy and identified correlations with phenotype and survival outcome. Forty-six pediatric patients with genetically verified mitochondrial encephalopathy and twenty-two controls investigated at the Queen Silvia Childrens Hospital, Sweden, were included. CSF lactate and neurofilament light (NF-L) were significantly increased in patients with mitochondrial encephalopathy compared to controls. Elevated CSF NF-L was associated with abnormal brain MRI and poorer survival. We suggest that CSF NF-L may be used in both clinical and research settings for monitoring the neurodegenerative process in mitochondrial disease.

Mitochondrial complex IV deficiency caused by a novel frameshift variant in MT-CO2 associated with myopathy and perturbed acylcarnitine profile

Mitochondrial myopathies are a heterogeneous group of disorders associated with a wide range of clinical phenotypes. We present a 16-year-old girl with a history of exercise intolerance since childhood. Acylcarnitine species suggestive of multiple acyl-CoA dehydrogenase deficiency were found in serum, however genetic analysis did not reveal variants in genes associated with this disorder. Biochemical analyses of skeletal muscle mitochondria revealed an isolated and extremely low activity of cytochrome c oxidase (COX). This finding was confirmed by enzyme histochemistry, which demonstrated an almost complete absence of fibers with normal COX activity. Whole-exome sequencing revealed a single base-pair deletion (m.8088delT) in MT-CO2, which encodes subunit 2 of COX, resulting in a premature stop codon. Restriction fragment length polymorphism-analysis confirmed mtDNA heteroplasmy with high mutant load in skeletal muscle, the only clinically affected tissue, but low levels in other investigated tissues. Single muscle fiber analysis showed segregation of the mutant genotype with respiratory chain dysfunction. Immuno-histochemical studies indicated that the truncating variant in COX2 has an inhibitory effect on the assembly of the COX holoenzyme.

OP5 – 2696: Pyruvate dehydrogenase complex deficiency: Phenotype–genotype, phenotype–neuroimaging associations and treatment outcomes

Objectives To assess the phenotypic and genotypic spectrum of patients with pyruvate dehydrogenase complex (PDHc) deficiency, identify phenotype–genotype correlations and evaluate the effect of ketogenic diet. Methods All patients investigated at the Queen Silvia Childrens Hospital and found to have genetically verified PDHc deficiency were included in this study. Results 18 patients (5 males: 13 females) were included; all but one patients were alive at a median follow-up period of 7.5 years. All patients were born at full term. Eleven patients (1 male: 10 females) presented with perinatal onset, consisting mainly of hypotonia, microcephaly and congenital lactic acidosis. These patients developed progressive microcephaly, severe mental retardation, while epilepsy was also seen in some patients. Brain neuroimaging in these patients revealed hypoplasia or complete agenesis of the corpus callosum, enlargement of the ventricles – often asymmetrical – and of the subarachnoid spaces and accompanying atrophy of the periventricular white matter. Genetic investigation showed variable genetic defects of the PDHA1 and PDHX genes. The remaining seven patients had later disease onset, at a median age of 1.5 years. The disease course in these patients pertained mainly to recurrent episodes of hypotonia, ataxia, dysarthria and hyperlactatemia, often following infections. All seven patients were found to have genetic defects in the PDHA1 gene. Brain neuroimaging showed bilateral lesions in the basal ganglia and the midbrain, while neuroimaging was normal in two patients. Thirteen patients were treated with ketogenic diet with positive effect, in the majority of treated patients, on the recurrent episodes of ataxia and dysarthria, speech development, mood and cognition. Conclusions We show that pediatric patients with PDHc deficiency express two different clinical phenotypes, each one correlated to specific neuroimaging features. The genetic background and the effect of ketogenic diet are assessed.