Homozygous W748S mutation in the POLG1 gene in patients with juvenile-onset Alpers syndrome and status epilepticus

POLG DNA testing as an emerging standard of care before instituting valproic acid therapy for pediatric seizure disorders

PURPOSE

To review our clinical experience and determine if there are appropriate signs and symptoms to consider POLG sequencing prior to valproic acid (VPA) dosing in patients with seizures.

METHODS

Four patients who developed VPA-induced hepatotoxicity were examined for POLG sequence variations. A subsequent chart review was used to describe clinical course prior to and after VPA dosing.

RESULTS

Four patients of multiple different ethnicities, age 3-18 years, developed VPA-induced hepatotoxicity. All were given VPA due to intractable partial seizures. Three of the patients had developed epilepsia partialis continua. The time from VPA exposure to liver failure was between 2 and 3 months. Liver failure was reversible in one patient. Molecular studies revealed homozygous p.R597W or p.A467T mutations in two patients. The other two patients showed compound heterozygous mutations, p.A467T/p.Q68X and p.L83P/p.G888S. Clinical findings and POLG mutations were diagnostic of Alpers-Huttenlocher syndrome.

CONCLUSION

Our cases underscore several important findings: POLG mutations have been observed in every ethnic group studied to date; early predominance of epileptiform discharges over the occipital region is common in POLG-induced epilepsy; the EEG and MRI findings varying between patients and stages of the disease; and VPA dosing at any stage of Alpers-Huttenlocher syndrome can precipitate liver failure. Our data support an emerging proposal that POLG gene testing should be considered in any child or adolescent who presents or develops intractable seizures with or without status epilepticus or epilepsia partialis continua, particularly when there is a history of psychomotor regression.

Status epilepticus: a critical review

Status epilepticus (SE) is a major neurological emergency with an incidence of about 20/100,000 and a mortality between 3 and 40% depending on etiology, age, status type, and status duration. Generalized tonic-clonic SE, in particular, requires immediate, aggressive, and effective treatment to stop seizure activity, and to prevent neuronal damage and systemic complications and death. Benzodiazepines and phenytoin/fosphenytoin are traditionally used as first-line drugs and are effective in about 60% of all episodes. However, a notable portion of patients remain in SE. For those, narcotics and induction of general anesthesia are used as second-line treatment. Therefore, there is a need for more effective first-line treatment options. Recently, valproic acid was approved for the treatment of status epilepticus in some European countries, and two of the newer antiepileptic drugs have become available for intravenous use: Levetiracetam (LEV) and lacosamide (LCM) should be evaluated in prospective controlled trials as possible treatment options. Standardized protocols for the management of SE are useful to improve immediate care.

Phenotypic variations in 3 children with POLG1 mutations

Autosomal inherited mitochondrial diseases have been of increasing interest among clinicians and mitochondrial research groups because these diseases are caused through a secondary effect on the mitochondrial DNA. It was thought that the genetic stability of mitochondrial DNA relies on the accuracy of DNA polymerase gamma. Mutations of DNA polymerase gamma 1 gene (MIM# 174763) have been shown to be a cause of mitochondrial disorders associated with Mendelian disorders characterized by multiple mitochondrial DNA deletions or depletions. To date, several clinical phenotypes associated with polymerase gamma mutation have been reported presenting in both adults and children. We present 3 children in whom were found to have reported pathogenic DNA polymerase gamma 1 mutations: heterozygous p.G517V in 2 half siblings and heterozygous p.T251I and p.P587L in the other. The aim of this communication is to report 3 pediatric cases associated with DNA polymerase gamma 1 mutations to augment the expanding clinical phenotype that has been previously reported.