PCDH11X and attention deficit-hyperactivity disorder: In another study two brothers with intellectual disability were identified with a 182 Kb duplication within intron 2 of PCDH11X, although their mildly affected sister was found not to carry the duplication.87 One interpretation of these findings is that an interruption of PCDH11X is less well tolerated in males than in females, a possible explanation of the male propensity to autism and attention deficit hyperactivity disorder.88