Complex sentence: General medical investigation usually reveals in children with true LGS, developmental delay and cognitive deficiencies, which may precede development of seizures, or require up to two years after the seizures begin in order to become apparent.
Split into simpler sentences: General medical investigation usually reveals developmental delay and cognitive deficiencies in children with true LGS. These may precede development of seizures, or require up to two years after the seizures begin, in order to become apparent.