Lhermitte-Duclos disease with concomitant KCNT2 gene mutation: report of an extremely rare combination.

Lhermitte-Duclos disease (LDD) refers to cerebellar dysplastic gangliocytoma, a slow-growing tumor. Pathogenic variants of voltage-gated potassium channels have been associated with epilepsy of variable severity. These include the sodium-activated potassium channel subfamily T member 2 (KCNT2) gene, which encodes for pore-forming alpha subunits. KCNT2 gene mutations have been recently described to cause developmental and epileptic encephalopathies (DEEs). The purpose of the present article is to describe an extremely rare case of a young child who has both LDD and KCNT2 mutation. Our patient is an 11-year-old boy who presented with an absence episode, and his investigations revealed electroencephalography (EEG) abnormalities, LDD, and a heterozygous KCNT2 mutation. Regarding LDD patients, epileptic seizures have been reported in very few cases. Reports of patients with mutated KCNT2 variants are also extremely rare. It is for sure that LDD and KCNT2 mutation is an extremely rare combination. Although further follow-up is mandatory in order to draw safe conclusions for our case, the available data support that our patient is either the first reported case of a subclinical KCNT2 mutation or the first case of its clinical expression in late childhood so far.