Intake and blood levels of fatty acids in treated patients with phenylketonuria

Background: Investigators in Italy and Spain have suggested that therapy fo r patients with phenylketonuria (PKU) may result in essential fatty acid (E FA) deficiency. Objectives of this study were to determine if the diets of patients with PKU in the United States provided adequate EFA intakes and wh ether patients could form long-chain polyunsaturated fatty acids. Methods: Patients (1-13 years of age) with classic PKU undergoing therapy a nd their non-PKU sibling closest in age were compared. Nutrient intakes wer e calculated from 3-day diet diaries. Fatty acids in plasma and erythrocyte s were identified and quantified, Paired t tests compared results for the p atients and their non-PKU siblings. Results: Twenty-eight patients and 26 siblings were studied, Mean fat intak e was greatest by siblings (34.8 +/- 1.3% of energy) and lowest by Phenyl-F ree-fed patients (19.5 +/- 1.2% of energy; P < 0.05). Fat intake (30.4 +/- 1.8% of energy) by Phenex-fed patients did not differ from that of siblings , Percentage of energy ingested as C18:2n-6 and C18:3n-3 did not differ sig nificantly between patients and siblings. No clinically significant, consis tent differences were found in fatty acid levels (wt%) in plasma or erythro cytes between patients with PKU and siblings. Conclusions: No patient in this study exhibited a Holman index of EFA defic iency. Siblings ingested animal protein containing C20:5n-3 and C22:6n-3 fa tty acids, and this may account for their greater wt% of these plasma and e rythrocyte fatty acids. Because patients with PKU do not ingest fatty acids >C18 but C20:4n-6, C20:5n-3, and C22:6n-3 were found in their plasma and e rythrocytes, in vivo synthesis from C18:2n-6 and C18:3n-3 appears to occur. Lack of EFA deficiency in patients in this study may be the result of the use of canola and soy oils containing C18:2n-6 and C18:3n-3 rather than oli ve oil in the diets.