. ▁The ▁baby ▁seems ▁normal ▁at ▁first ▁but ▁actually ▁inc urs ▁permanent ▁intellectual ▁dis ability . ▁This ▁can ▁cause ▁sympt oms ▁such ▁as ▁mental ▁ret ard ation , ▁ab normal ▁g ait ▁and ▁post ure , ▁and ▁delayed ▁growth . ▁Because ▁ty ros ine ▁is ▁used ▁by ▁the ▁body ▁to ▁make ▁mel an in ▁( a ▁component ▁of ▁the ▁p ig ment ▁found ▁in ▁the ▁hair ▁and ▁skin ), ▁failure ▁to ▁convert ▁normal ▁levels ▁of ▁phen yl al an ine ▁to ▁ty ros ine ▁can ▁lead ▁to ▁fair ▁hair ▁and ▁skin . ▁The ▁frequency ▁of ▁this ▁disease ▁var ies ▁greatly . ▁Specifically , ▁in ▁the ▁United ▁States , ▁PK U ▁is ▁found ▁at ▁a ▁rate ▁of ▁nearly ▁ 1 ▁in ▁ 1 0 , 0 0 0 ▁birth s . ▁Due ▁to ▁new born ▁screen ing , ▁do ctors ▁are ▁able ▁to ▁detect ▁PK U ▁in ▁a ▁baby ▁sooner . ▁This ▁allows ▁them ▁to ▁start ▁treatment ▁early , ▁prevent ing ▁the ▁baby ▁from ▁suffering ▁from ▁the ▁severe ▁effects ▁of ▁PK U . ▁PK U ▁is ▁caused ▁by ▁a ▁mut ation ▁in ▁the ▁PA H ▁gene , ▁whose ▁role ▁is ▁to ▁instruct ▁the ▁body ▁on ▁how ▁to ▁make ▁phen yl al an ine ▁hydro x yl ase . ▁Ph en yl al an ine ▁hydro x yl ase ▁is ▁what ▁converts ▁the ▁phen yl al an ine , ▁taken ▁in ▁through ▁di et , ▁into ▁other ▁things ▁that ▁the ▁body ▁can ▁use . ▁The ▁mut ation ▁often ▁decre ases ▁the ▁effect iveness ▁or ▁rate