Disclosed is a method for preparing a composition enriched for receptors(typically molecular impringet polymers,MIPs) that bind an agent, where said receptors each specifically bind at leasttwo discrete sites on said agent, by subjecting a sampleof receptors to a first step of affinity purification with the agent where onebinding site on the agent is non-accessible for bindingto the receptors and subsequently subjecting the purified receptors to atleast one further step of affinity purification with theagent where a second binding site on the agent is non-accessible. Alsodisclosed is a method for treatment, amelioration or prophylaxisof a disease selected from the group consisting of phenylketonuria (PKU,F.slzero.lling's disease), hyperphenylalaninemia(HPA), alcaptonuria (black urine disease), tyrosinemia, hypertyrosinemia,myasthenia gravis, histidinemia, urocanic aciduria,maple syrup urine disease (MSUD), isovaleric acidemia (isovaleryl-CoAdehydrogenase deficiency), homocystinuria, propionicacidemia, methylmalonic acidemia, and glutaric aciduria Type 1 (GA-I),galactosemia, comprising administering to the gastrointestinaltract of a patient in need thereof an effective amount of a composition ofmolecular imprinted polymers (MIPs), said compositionbeing capable of binding a symptom provoking agent of said disease.
