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We report the case histories of identical twin brothers who developed concordant acute lymphoblastic leukemia at the age of 4 years and who later developed leukoencephalopathy and hydrocephalus related to central nervous system prophylaxis by, in the first case intrathecally administered methotrexate and, in the second by intrathecally administered methotrexate and cranial irradiation.
 ( adverse event: developed ,  identical twin brothers: Subject, brothers: Subject.Gender, leukoencephalopathy and hydrocephalus: Effect, intrathecally administered methotrexate: Treatment, intrathecally administered methotrexate and cranial irradiation: Treatment, methotrexate: Treatment.Drug, methotrexate: Treatment.Drug, intrathecally: Treatment.Route, intrathecally: Treatment.Route) 
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: adverse event,potential therapeutic event, Arguments type: Treatment.Disorder,Treatment.Time_elapsed,Treatment.Dosage,Subject.Race,Treatment.Drug,Treatment.Route,Subject.Disorder,Treatment.Freq,Treatment,Effect,Subject.Population,Treatment.Duration,Combination.Drug,Subject,Subject.Age,Subject.Gender. 
Text: {0} 
Answer:
 ( adverse event: developed ,  identical twin brothers: Subject, brothers: Subject.Gender, leukoencephalopathy and hydrocephalus: Effect, intrathecally administered methotrexate: Treatment, intrathecally administered methotrexate and cranial irradiation: Treatment, methotrexate: Treatment.Drug, methotrexate: Treatment.Drug, intrathecally: Treatment.Route, intrathecally: Treatment.Route) 