GM3 synthase (ST3GAL5) deficiency, which was originally identified in Old Order Amish individuals, is responsible for an autosomal recessive infantile-onset symptomatic epilepsy syndrome associated with intractable seizures, developmental stagnation, extreme irritability, failure to thrive, cortical blindness, and cutaneous dyspigmentation (26–28). Here, ST3GAL5 is linked to GM3 synthase deficiency.