Personalized multidisciplinary care improves glycemic control, phenylalanine in co-occurring Phenylketonuria, Type 1 Diabetes.

Coexistence of Phenylketonuria (PKU) and Type 1 Diabetes (T1DM) presents a unique and complex nutritional challenge. Both are lifelong metabolic disorders requiring strict dietary management, often with conflicting strategies. PKU necessitates a severely restricted phenylalanine intake, while T1DM requires careful carbohydrate management and insulin titration. The transition from pediatric to adult care for such patients is particularly challenging, often leading to poor adherence and suboptimal metabolic control. This case highlights the need for integrated approaches to manage these rare, yet demanding, dual diagnoses.

A 27-year-old man with longstanding Phenylketonuria was referred to an adult metabolic-diabetes center after a new diagnosis of Type 1 Diabetes. Initially, he was on fixed insulin doses and struggled with adherence to his PKU diet, leading to increased conventional protein intake. The intervention involved structured therapeutic education, a transition from fixed insulin doses to a dynamic regimen based on carbohydrate counting, and a revision of medical nutrition therapy using PKU-adapted low-protein foods and sugar-free phenylalanine-free amino acid supplements. Clinical, biochemical, nutritional, and continuous glucose monitoring (CGM) data were reviewed.

At T1DM diagnosis, the patient's HbA1c was 11.5%, with markedly reduced C-peptide levels and high titer anti-GAD antibodies. Initial diabetes management was associated with poor adherence to the PKU diet, increased intake of conventional protein sources, and elevated phenylalanine levels. After individualized insulin titration and nutritional intervention, significant improvements were observed:

HbA1c improved from 11.5% to 7.8%, phenylalanine levels decreased from 842 to 705 μmol/L, and insulin requirement declined from 0.55 to 0.3 IU/kg/day. Continuous glucose monitoring showed improved glycemic control without increased hypoglycemia. The Glycemia Risk Index also improved significantly, moving from high-risk Zone E to low-intermediate-risk Zone B, indicating better overall glucose management and reduced variability.