Intractable Epilepsy in Maternally Inherited Leigh Syndrome (MILS) Due to the Sporadic Variant m.8993T>G in MT-ATP6: A Case Report

Epilepsy is a common phenotypic feature of Leigh syndrome. However, data about the characteristics, treatments, and outcomes of epilepsy in maternally inherited Leigh syndrome (MILS) are limited. A four-year-old boy with sporadic MILS developed epilepsy at the age of five months. His condition was diagnosed at birth and was caused by the m.8993T>G variant with a heteroplasmy rate of 90% in skin fibroblasts. The patient presented with absences, and focal and generalized tonic-clonic seizures. Despite treatment with anti-seizure drugs such as vigabatrin, lamotrigine, clonazepam, diazepam, clobazam, and phenobarbital, seizure control was insufficient, and seizures became intractable. The patient died after recurrent aspiration, pneumonia, and sepsis. In conclusion, the m.8993T>G variant can occur sporadically, and m.8993T>G carriers with MILS may develop epilepsy as the disease progresses. Moreover, the treatment for epilepsy in MILS can be challenging, and epilepsy can become intractable and can contribute to fatal outcomes.