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

BACKGROUND

Investigators in Italy and Spain have suggested that therapy for patients with phenylketonuria (PKU) may result in essential fatty acid (EFA) deficiency. Objectives of this study were to determine if the diets of patients with PKU in the United States provided adequate EFA intakes and whether patients could form long-chain polyunsaturated fatty acids.

METHODS

Patients (1-13 years of age) with classic PKU undergoing therapy and their non-PKU sibling closest in age were compared. Nutrient intakes were calculated from 3-day diet diaries. Fatty acids in plasma and erythrocytes were identified and quantified. Paired t tests compared results for the patients and their non-PKU siblings.

RESULTS

Twenty-eight patients and 26 siblings were studied. Mean fat intake was greatest by siblings (34.8 +/- 1.3% of energy) and lowest by Phenyl-Free-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 significantly between patients and siblings. No clinically significant, consistent differences were found in fatty acid levels (wt%) in plasma or erythrocytes between patients with PKU and siblings.

CONCLUSIONS

No patient in this study exhibited a Holman index of EFA deficiency. Siblings ingested animal protein containing C20:5n-3 and C22:6n-3 fatty acids, and this may account for their greater wt% of these plasma and erythrocyte 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 erythrocytes, 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 olive oil in the diets.