Rapidly Progressive Neurological Deterioration in a Child with Alpers Syndrome Exhibiting a Previously Unremarkable Brain MRI
ABSTRACT Alpers syndrome is a fatal disorder due to mutations in the POLG gene encoding the catalytic subunit of mitochondrial DNA polymerase gamma (Pol gamma) involved in mitochondrial DNA (mtDNA) replication. We describe a case of Alpers syndrome due to POLG mutations, with rapidly progressive course, a fatal outcome, and an essentially normal brain MRI in the early oligo-symptomatic phase. Our observation suggests that Alpers syndrome should be considered even in patients with an initially unremarkable brain MRI. The patient was found to harbor the p.Q497H, p.W748S and p.E1143G mutations in cis on one allele, and a fourth mutation, the p.G848S on the other allele. Although the individual mutations detected in the presented case have been previously reported, the specific genotype formed by the particular combination of these is novel.
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ABSTRACT: Mutations in the POLG gene have emerged as one of the most common causes of inherited mitochondrial disease in children and adults. They are responsible for a heterogeneous group of at least 6 major phenotypes of neurodegenerative disease that include: 1) childhood Myocerebrohepatopathy Spectrum disorders (MCHS), 2) Alpers syndrome, 3) Ataxia Neuropathy Spectrum (ANS) disorders, 4) Myoclonus Epilepsy Myopathy Sensory Ataxia (MEMSA), 5) autosomal recessive Progressive External Ophthalmoplegia (arPEO), and 6) autosomal dominant Progressive External Ophthalmoplegia (adPEO). Due to the clinical heterogeneity, time-dependent evolution of symptoms, overlapping phenotypes, and inconsistencies in muscle pathology findings, definitive diagnosis relies on the molecular finding of deleterious mutations. We sequenced the exons and flanking intron region from approximately 350 patients displaying a phenotype consistent with POLG related mitochondrial disease and found informative mutations in 61 (17%). Two mutant alleles were identified in 31 unrelated index patients with autosomal recessive POLG-related disorders. Among them, 20 (67%) had Alpers syndrome, 4 (13%) had arPEO, and 3 (10%) had ANS. In addition, 30 patients carrying one altered POLG allele were found. A total of 25 novel alterations were identified, including 6 null mutations. We describe the predicted structural/functional and clinical importance of the previously unreported missense variants and discuss their likelihood of being pathogenic. In conclusion, sequence analysis allows the identification of mutations responsible for POLG-related disorders and, in most of the autosomal recessive cases where two mutant alleles are found in trans, finding deleterious mutations can provide an unequivocal diagnosis of the disease.Human Mutation 09/2008; 29(9):E150-72. DOI:10.1002/humu.20824 · 5.05 Impact Factor
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ABSTRACT: Deoxyguanosine kinase (dGK) deficiency is a frequent cause of mitochondrial DNA depletion associated with a hepatocerebral phenotype. In this study, we describe a new splice site mutation in the DGUOK gene and the clinical, radiologic, and genetic features of these DGUOK patients. This new DGUOK homozygous mutation (c.444-62C>A) was identified in three patients from two North-African consanguineous families with combined respiratory chain deficiencies and mitochondrial DNA depletion in the liver. Brain MRIs are normal in DGUOK patients in the literature. Interestingly, we found subtentorial abnormal myelination and moderate hyperintensity in the bilateral pallidi in our patients. This new mutation creates a cryptic splice site in intron 3 (in position −62) and is predicted to result in a larger protein with an in-frame insertion of 20 amino acids. In silico analysis of the putative impact of the insertion shows serious clashes in protein conformation: this insertion disrupts the α5 helix of the dGK kinase domain, rendering the protein unable to bind purine deoxyribonucleosides. In addition, a common haplotype that segregated with the disease in both families was detected by haplotype reconstruction with 10 markers (microsatellites and SNPs), which span 4.6 Mb of DNA covering the DGUOK locus. In conclusion, we report a new DGUOK splice site mutation that provide insight into a critical protein domain (dGK kinase domain) and the first founder mutation in a North-African population.Molecular Genetics and Metabolism 03/2009; 97(3-97):221-226. DOI:10.1016/j.ymgme.2009.03.007 · 2.83 Impact Factor
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ABSTRACT: Mitochondrial disorders result from primary defects in the mitochondrial DNA (mtDNA) or from defects in nuclear genes which cause disease by affecting the mtDNA. POLG1 is a nuclear gene which encodes for the catalytic subunit of the mtDNA polymerase gamma, essential for mtDNA replication. Less than a decade ago, POLG1 mutations were discovered in patients with progressive external ophthalmoplegia. Since then, it has emerged that POLG1 mutations can result in a spectrum of clinical manifestations, resulting in autosomal recessive or dominant mitochondrial diseases. Here we summarize the common clinical phenotypes associated with POLG1 mutations. Alpers syndrome, progressive external ophthalmoplegia with or without limb myopathy, ataxia-neuropathy syndrome, and epilepsy are frequent clinical manifestations of the POLG1-related disease. Childhood progressive encephalopathy, Parkinsonism, stroke-like events, and isolated exercise intolerance can occur in association with POLG1 mutations. Muscle biopsy can show signs of mitochondrial dysfunction by histologic and biochemical studies or it can be unrevealing. mtDNA analysis of affected tissues can reveal depletion, multiple deletions or point mutations, but it can be occasionally noninformative by routine analysis. : POLG1 mutations result in extremely heterogenous phenotypes which often have overlapping clinical findings, making it difficult to categorize patients into syndromes. The lack of signs of mitochondrial dysfunction in the muscle biopsy does not exclude a POLG1-related disease. Analysis of mtDNA of clinically affected tissues is often informative, but not always. Molecular analysis of POLG1 is essential when POLG1-related disease is suspected. Sodium valproate should be avoided because of the risk of liver failure.The Neurologist 03/2010; 16(2):84-91. DOI:10.1097/NRL.0b013e3181c78a89 · 1.08 Impact Factor