Novel PRKAR1B Variant Responding to Topiramate in a Lebanese Child

Patients with PRKAR1B gene variants can present with a neurodegenerative disease in adults or a cognitive delay, behavioral problems and regression in children causing Marbach-Schaaf Neurodevelopmental Syndrome (MASNS) which is a rare autosomal dominant disease. However with less of 30 reported cases in Literature, the clinical spectrum of PRKAR1B gene mutations remains to be explored, and the treatment remains challenging. In this paper, we report the cases of a Lebanese child with previously unreported missense PRKAR1B variant presenting with a massive arachnoid cyst, speech delay, cognitive delay, behavioral dysregulation and developmental regression at 2 years of age. The patient showed behavioral response to treatment with a low dose of topiramate. This case expands the known genotypic and phenotypic spectrum of this recently described disorder, highlighting the importance of genetic investigation in children with cognitive delay.