(A) Mental age-equivalent scores of MPSIH patients receiving related-donor BMT before 24 months of age (normal, —; slope ≥ .50, ○; slope .25 to .49, □; solid symbol denotes most recent neuropsychologic evaluation). (B) Mental age-equivalent scores of MPSIH patients receiving related-donor BMT after 24 months of age (normal, —; slope ≥ .50, ○; slope .25 to .49, □; slope < .25, ◊; solid symbol denotes most recent neuropsychologic evaluation). *Latest neuropsychologic evaluation at 159 months of age and a mental age-equivalent score of 108 months.