Endocrine Abstracts

Background: The standard, lifelong therapy of phenylketonuria (PKU) is natural protein-restricted diet completed with Phenylalanine (Phe)-free L-amino acid mixtures that provide the daily necessary micronutrients, such as iodine and selenium. Our main objective in this study was to assess the iodine and selenium status of patients with PKU, based on their adherence to the low-Phe diet, compared to a healthy control group. Secondly, we aimed to asses whether adherence to therapy has any effect on thyroid function and structure of PKU patients.

Methods: A single-center, case-control study was conducted with seventy-seven PKU patients (age 18–41 years) and 50 matched healthy controls. Thyroid hormones, serum thyroglobulin (Tg), thyroid antibodies (TgAb, TPOAb), urinary iodine (UIC) and selenium concentrations (USeC) were measured, and thyroid ultrasound was performed.

Results: Although optimal iodine status was found in the entire PKU population, by dividing the patients according to their therapy compliance significantly higher median urinary iodine concentration was found in the control and good adherence group compared to the low adherence group (control: 145 μg/l good adherence: 165 μg/L vs. low adherence: 61 μg/l, P=0.001, and P<0.001, respectively). Median urinary selenium concentration was comparable between control and good adherence groups (21 vs 21 μg/g), whereas low adherence group had significantly lower USeC levels (16 μg/g, P=0.019, and P=0.017, respectively). The incidence of thyroid dysfunction in the PKU group was infrequent (5%). Median serum TSH was significantly higher in the control the (P=0.018) and good adherence (P<0.001) groups compared to low adherence group, without any free thyroid hormones changes. TSH levels in PKU group showed a negative correlation with Phe levels (rs =−0.34, P=0.005). Thyroid antibody (TgAb and/or TPOAb) positivity was found to be similar to those detected in the control group and the general population. No significant difference in thyroid volume and nodularity has been observed between the good adherence, low adherence and control group.

Conclusions: The results of this study suggest that iodine status is strongly influenced by the adherence to therapy in early-treated adult PKU patients. Protein-restricted diet combined with Phe-free L-amino acid mixtures provide adequate iodine intake. No or not enough medical food consumption combined with a low-Phe diet can lead to subclinical iodine deficiency, but it does not influence thyroid function.