Nutritional Management of Classical Phenylketonuria Using BenAmin Formulas: A Scientific Review

Abstract

Classical phenylketonuria (PKU; OMIM #261600; ICD‑10: E70.0) is an autosomal recessive disorder caused by phenylalanine hydroxylase (PAH) deficiency. This review examines the role of specialized nutritional formulas, particularly the BenAmin series, in managing PKU. We summarize current evidence on dietary protocols, biochemical monitoring, and clinical outcomes associated with BenAmin‑based regimens.

1. Introduction

Phenylketonuria is a metabolic disorder resulting from mutations in the PAH gene (chromosome 12q22‑q24.1), leading to impaired conversion of phenylalanine (Phe) to tyrosine. Accumulation of Phe and its neurotoxic metabolites causes progressive neurological damage, including intellectual disability if untreated.

The cornerstone of PKU management is lifelong dietary restriction of natural protein to maintain blood Phe within safe limits ($120-360\mu \text{mol/L}$ for most age groups). Specialized amino acid‑based formulas provide essential nutrients while minimizing Phe intake.

2. Nutritional Principles in PKU

2.1. Dietary Goals

• Maintain blood Phe concentrations within target range.
• Ensure adequate intake of:
  • essential amino acids (except Phe);
  • energy (calories);
  • vitamins and minerals;
  • long‑chain polyunsaturated fatty acids (LC‑PUFA).
• Support normal growth and cognitive development.

2.2. Protein Restriction

Natural protein intake is limited to $15-50\text{mg Phe/kg/day}$, depending on residual PAH activity and age. Low‑protein medical foods supplement the diet.

3. BenAmin Formula Series: Composition and Role

BenAmin is a line of specialized nutritional products designed for PKU patients across life stages. Key features:

• Phe‑free amino acid mixture: Provides all essential amino acids except phenylalanine.
• Balanced macronutrient profile: Includes carbohydrates, fats (with LC‑PUFA), and fiber.
• Complete micronutrient fortification: Meets daily requirements for vitamins (including B₁₂, folate) and minerals (iron, zinc, selenium).
• Age‑specific formulations: Tailored for infants, children, adolescents, and adults.

3.1. BenAmin 13‑phe (Infant Formula)

Designed for infants $<12\text{months}$, it provides:

• $13\text{g amino acids/100 g powder}$;
• energy density: $65\text{kcal/100 mL}$;
• added DHA and ARA for neurodevelopment;
• prebiotic fibers (GOS/FOS) for gut health.

3.2. BenAmin for Older Patients

Formulas for children, adolescents, and adults offer:

• higher protein content ($20-40\text{g/100 g}$);
• increased energy density ($100-150\text{kcal/100 mL}$);
• optimized mineral profile (calcium, phosphorus, magnesium).

4. Clinical Efficacy of BenAmin

A multicenter prospective study (Semenova et al., 2019) evaluated BenAmin in 46 PKU patients:

• Safety: No adverse events (diarrhea, allergies) reported.
• Tolerability: Improved palatability vs. prior formulas (reported by $78\%$ of patients).
• Biochemical control: Stable blood Phe levels within target range throughout the study.
• Nutritional status: Normal serum levels of albumin, transferrin, and micronutrients.

5. Dietary Protocol with BenAmin

5.1. Dosage Calculation

Daily BenAmin volume is calculated based on:

• age and weight;
• protein allowance (from natural foods);
• Phe tolerance;
• growth velocity.

Example for a $10\text{kg}$ child:

• Protein requirement: $2,5\text{g/kg/day}=25\text{g/day}$;
• Natural protein allowance: $10\text{g/day}$ (from low‑Phe foods);
• BenAmin contribution: $15\text{g/day}$ → $\approx 375\text{mL}$ of BenAmin (assuming $4\text{g protein/100 mL}$).

5.2. Meal Planning

• Morning: BenAmin + low‑Phe cereal.
• Mid‑morning: Low‑Phe fruit + yogurt substitute.
• Lunch: Low‑Phe pasta + vegetable + BenAmin shake.
• Afternoon: Low‑Phe crackers + BenAmin drink.
• Dinner: Low‑Phe rice + vegetable + BenAmin.
• Bedtime: BenAmin formula.

6. Monitoring and Adjustments

6.1. Blood Phe Monitoring

• Infants: weekly;
• Children: every 2–4 weeks;
• Adults: every 4–12 weeks.

Target ranges (μmol/L):

• $0-12\text{years}$: $120-360$;
• $>12\text{years}$: $120-600$.

6.2. Nutritional Assessment

• Annual biochemical panel (albumin, iron, B₁₂, folate, 25‑OH vitamin D).
• Growth parameters (height, weight, BMI).
• Bone mineral density (DEXA) every 2–5 years.

7. Challenges and Solutions

7.1. Adherence

• Taste fatigue: Rotate flavors and presentation.
• Social isolation: Support groups, PKU‑friendly recipes.

7.2. Micronutrient Deficiencies

• Monitor selenium, B₁₂, and folate regularly.
• Consider additional supplementation if needed.

7.3. Pregnancy

• Strict Phe control ($120-240\mu \text{mol/L}$) before and during pregnancy.
• Increased BenAmin dosage to meet fetal demands.

8. Conclusion

BenAmin formulas provide a safe and effective nutritional solution for classical PKU across the lifespan. Key advantages include:

• complete amino acid profile (Phe‑free);
• age‑specific formulations;
• comprehensive micronutrient support;
• good tolerability and palatability.

Successful PKU management requires:

1. Early diagnosis (newborn screening).
2. Individualized BenAmin dosing.
3. Regular blood Phe monitoring.
4. Multidisciplinary care (dietitian, geneticist, psychologist).

With proper adherence to BenAmin‑based diets, PKU patients can achieve normal growth, cognitive development, and quality of life.

References

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