Complex sentence: Microcephaly has a wide range of prognoses: some patients experience little to very little mental retardation and can reach regular age-appropriate milestones, while others experience severe mental retardation and neuromuscular side effects.
Split into simpler sentences: Microcephaly has a wide range of prognoses: some patients experience little to very mental retardation and can reach regular age-appropriate milestones. Others may experience severe mental retardation and neuromuscular side effects.