Chronic kidney disease in adolescent and adult patients with phenylketonuria

Objectives A lifelong phenylalanine-restricted diet with supplementation of a phenylalanine-free amino acid formula is recommended in patients with phenylketonuria (PKU). The effect of a long-term PKU diet on renal function and blood pressure has not been investigated yet. Design We analyzed renal function in 67 patients with PKU, aged 15–43 years, by measuring glomerular filtration rate (GFR) and effective renal plasma flow by isotope clearance ( 51 Cr-EDTA, 123 J-Hippuran), estimated GFR, blood retention parameters, urinary protein and electrolyte excretion. Renal ultrasound and 24 h ambulatory blood pressure monitoring were performed additionally. Patients were divided into three groups according to their: 1) current diet (CD), i.e., daily protein intake: I CD 1.04 g/kg; 2) life-long diet time (LDT), i.e., cumulative years of life in which daily protein intake exceeded dietary recommendations: I LDT 19 years. Results GFR was decreased in 19 % of the patients. With increasing protein intake, GFR decreased significantly (I CD 111 ml/min; II CD 105 ml/min; III CD 99 ml/min. I LDT 112 ml/min; II LDT 103 ml/min; III LDT 99 ml/min). Proteinuria was detected in 31 %, microalbuminuria in 7 %, and hypercalciuria in 23 % of the patients. 23 % of the patients had arterial hypertension, and 41 % revealed a nocturnal non-dipping status. Conclusions In patients with PKU on a lifelong diet we could detect impaired renal function in 19 %, proteinuria in 31 %, and arterial hypertension in 23 %. Thus, chronic kidney disease may develop in PKU patients, and routine renal function tests should be performed during long-term follow-up.