Biallelic ST3GAL5 loss-of-function variants result in systemic ganglioside deficiency, an infantile-onset neurodevelopmental syndrome characterized by intractable epileptic encephalopathy, auditory and visual impairment, global psychomotor delay, extrapyramidal movements, and untimely death. The gene discussed is ST3GAL5; the disease is Epileptic encephalopathy.