Nutrition Spotlight: Protein Metabolism Disorders

Posted on Feb. 22nd, 2011 at 4:30pm

Below is the first post in what will be a continuing series of brief articles compiled by the Mead Johnson research team about common topics in infant nutrition. All topics can be found by visiting the Nutrition and Your Child page.

Metabolic disorders, or inborn errors of metabolism, are inherited genetic diseases in which a baby is unable to metabolize a specific nutrient. Without appropriate dietary management, the unmetabolized nutrient and metabolic by-products will accumulate in the body, and may result in adverse effects that inhibit normal growth and development. However, many infants who start treatment early in life can grow and develop normally. Mead Johnson Nutrition is a pioneer in the field of specialized nutrition for metabolic disorders and has been a leader in the development of science-based metabolic products for more than 50 years.

Protein Metabolism Disorders

Protein is a key constituent of most foods we eat, including meat, beans, milk products and grains. Infants with protein metabolism disorders cannot drink human milk because it also contains proteins and amino acids that cannot be metabolized. Infants with protein metabolism disorders are unable to metabolize certain amino acids and require specialized formulas without the offending amino acid, allowing the baby to receive essential nutrients for growth.

Examples of protein metabolism disorders include:

  • Phenylketonuria (PKU)
  • Maple Syrup Urine Disease (MSUD)
  • Tyrosinemia
  • Homocystinuria

A Closer Look at Phenylketonuria (PKU)

Phenylketonuria, often referred to as PKU, is one of the most common protein metabolism disorders. Normally, the human body metabolizes the essential amino acid phenylalanine into tyrosine. Infants with PKU do not have the enzyme needed to make this conversion. Consequently, their bodies have excess amounts of phenylalanine and low tyrosine levels. The following symptoms may result from untreated PKU:

  • Lethargy

  • Intellectual disability

  • Light pigment

  • Seizures

  • Eczema

  • Hyperactivity

Dietary management is critical for individuals with PKU to assure normal growth and development, as well as to support normal neurocognitive function. Fortunately, PKU can be diagnosed early in life through genetic disorders screenings, which are mandatory in many countries. Once diagnosed, the dietary management of PKU can start right away.

PKU management involves a highly restrictive diet that minimizes the amount of phenylalanine consumed and regular monitoring by healthcare professionals experienced in the dietary management of metabolic diseases. For infants with PKU, special phenylalanine-free formulas act as their primary source of protein. Regular clinic visits allow monitoring phenylalanine in the blood and the growth of the infant to ensure that the dietary management is successful.