POLG1 manifestations in childhood.

OBJECTIVE: Mitochondrial DNA polymerase γ (POLG1) mutations in children often manifest as Alpers syndrome, whereas in adults, a common manifestation is mitochondrial recessive ataxia syndrome (MIRAS) with severe epilepsy. Because some patients with MIRAS have presented with ataxia or epilepsy already in childhood, we searched for POLG1 mutations in neurologic manifestations in childhood. METHODS: We investigated POLG1 in 136 children, all clinically suspected to have mitochondrial disease, with one or more of the following: ataxia, axonal neuropathy, severe epilepsy without known epilepsy syndrome, epileptic encephalopathy, encephalohepatopathy, or neuropathologically verified Alpers syndrome. RESULTS: Seven patients had POLG1 mutations, and all of them had severe encephalopathy with intractable epilepsy. Four patients had died after exposure to sodium valproate. Brain MRI showed parieto-occipital or thalamic hyperintense lesions, white matter abnormality, and atrophy. Muscle histology and mitochondrial biochemistry results were normal in all. CONCLUSIONS: POLG1 analysis should belong to the first-line DNA diagnostic tests for children with an encephalitis-like presentation evolving into epileptic encephalopathy with liver involvement (Alpers syndrome), even if brain MRI and morphology, respiratory chain activities, and the amount of mitochondrial DNA in the skeletal muscle are normal. POLG1 analysis should precede valproate therapy in pediatric patients with a typical phenotype. However, POLG1 is not a common cause of isolated epilepsy or ataxia in childhood.

Mitochondrial DNA polymerase gamma variants in idiopathic sporadic Parkinson disease.

OBJECTIVE: Dysfunction of mitochondrial DNA polymerase gamma (POLG) has been recently recognized as an important cause of inherited neurodegenerative diseases. We have reported dominant and recessive inheritance of parkinsonism, mitochondrial myopathy, and premature amenorrhea in five ethnically distinct families with POLG1 mutations. This prompted us to carry out a detailed analysis of the coding region and intron-exon boundaries of POLG1 in Finnish patients with idiopathic sporadic Parkinson disease (PD) and in nonparkinsonian controls. METHODS: The coding region of POLG1 was analyzed in 140 Finnish patients with PD and their 127 spouses as age- and ethnically matched controls. Further, we analyzed the intragenic CAG-repeat region of POLG1 in 126 additional patients with nonparkinsonian neurologic disorders and in 516 Finnish population controls. RESULTS: We found clustering of rare variants of the POLG1 CAG-repeat, encoding a polyglutamine tract, in Finnish patients with idiopathic PD as compared to their spouses (p = 0.003; OR 3.01, 95% CI 1.35 to 6.71), population controls (p = 0.001; OR 2.45, 95% CI 1.45 to 4.14), and patients with nonparkinsonian neurologic disorders (p = 0.05, OR 1.98, 95% CI 0.97 to 4.05). We found several amino acid substitutions, none of them associating with PD. These included a previously parkinsonism-associated POLG variant Y831C, found in one patient with PD, but also in five controls, suggesting that it is a neutral amino acid polymorphism. CONCLUSIONS: Our results suggest that POLG polyglutamine tract variants should be considered as a predisposing genetic factor in idiopathic sporadic Parkinson disease.