Mental retardation, which occurs in phenylketonuric patients, is associated with increased levels of phenylalanine, increased
oxidative stress, and an imbalance of amino acids in the brain. Recent studies have shown that oxidative stress plays a role
in the pathogenesis of phenylketonuria. In this work, we aimed to compare the infuence of blood phenylalanine levels on
oxidative stress parameters in phenylketonuric patients who divided patients into groups according to blood Phe levels
during follow-up visits and compared these groups with healthy controls. Results showed signifcant diferences in glutathione peroxidase (GSHPx), coenzyme Q10 (Q10), Q10/cholesterol, and l-carnitine levels in phenylketonuria patients
and the control group. GSHPx, Q10, and Q10/cholesterol levels were signifcantly lower in poor adherence patients than in
the control groups. l-carnitine levels were signifcantly increased in good adherence patients than poor adherence patients
and decreased in poor adherence patients than healthy controls. No correlations were observed between phenylalanine and
l-carnitine concentrations in poor adherence group. No signifcant diferences were observed in paraoxonase 1 (PON1),
total antioxidant status (TAS), total oxidant status (TOS) and oxidative stress index (OSI) levels. As a result, in this work,
poor adherence patients are prone to oxidative stress. Although the patients may have the same diagnosis, patients have
diferent clinical characteristics and diferent prognosis. Antioxidants can be used as an adjuvant therapy in order to avoid
neurological damage in these patients.

• Efect of Blood Phenylalanine Levels on Oxidative Stress in Classical Phenylketonuric Patients