Arginase deficiency- an unheralded cause of developmental epileptic encephalopathy.

Arginase deficiency, that leads to hyperargininaemia is a rare urea cycle disorder caused by mutation in ARG1 gene. It is an under recognized cause of paediatric developmental epileptic encephalopathy, with the key coexistent clinical features being developmental delay or regression and spasticity. Detection of ARG1 gene mutation on genetic testing is the confirmatory diagnostic test. However, elevated levels of plasma arginine and low plasma arginase level can be considered as biochemical markers for diagnosis. We present two cases of arginase deficiency with genetically confirmed ARG1 mutation in one and biochemical confirmation in both. As the spectrum of epilepsy in arginase deficiency has been less explored, we attempted to elucidate the novel electroclinical features and syndromic presentations in these patients. Informed consent was obtained from families of patients. Electroclinical diagnosis was consistent with Lennox Gastaut syndrome (LGS) in the first patient while the second patient had refractory atonic seizures with electrophysiological features consistent with developmental and epileptic encephalopathy. Though primary hyperammonaemia is not a consistent feature, secondary hyperammonaemia in the setting of infectious triggers and drugs like valproate (valproate sensitivity) has been well described as also observed in our patient. In the absence of an overt antecedent in a child with spasticity and seizure disorder, with a progressive course consistent with a developmental epileptic encephalopathy, arginase deficiency merits consideration. Diagnosis often has important therapeutic implications with respect to dietary management and choice of the appropriate antiseizure medications.