bannie, i have classical pku- i did respond to the kuvan. it just depends on the individual, we all will respond differently and how much extra phe you will be able to add also depends on the individual response to the kuvan. personally, i haven't been able to add alot . i have severe asthma, which seems to increase my levels. when i have asthma attacks my levels go higher so my intake is being constantly adjusted depending on how well my asthma is being controlled. i have only been able to go from375mgs/phe to around 500. it is likely to be much different for you. if i were in yoour position i'd try the kuvan…worst possible senerio, you're not a responder, then you're no worse off than before the kuvan. try it and see if it works for you.