Metabolic disorders in babies affect how infants digest food and convert it into fuel for the body. These infants may lack certain digestive enzymes that allow people to use certain nutrients.

As a result, babies may become weak, be lethargic, and experience digestive issues. However, symptoms vary widely according to the specific disorder.

These rare conditions are often genetic. Doctors screen babies for a range of these conditions in the first 2 days following birth.

This article looks at metabolic disorders in babies, as well as the causes, symptoms, and diagnosis.

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Metabolic disorders in infants are conditions that affect the way the body uses food and converts it into energy. Some of these disorders can be serious. If left untreated, metabolic disorders may affect a baby’s health and development, and, in some cases, they may be life threatening.

In a healthy infant, enzymes in the digestive tract break down or metabolize breast milk or formula into sugars, fats, and amino acids. The body uses these compounds immediately or stores them for use later.

In infants with metabolic disorders, this process does not occur as it should. Instead, the body has too much or too little of substances such as amino acids and glucose (sugar). These nutritional imbalances can lead to health issues.

There are over 700 metabolic disorders that can impact infants and babies. Doctors may also refer to these as inborn errors of metabolism or inherited metabolic disorders.

In the United States, the Health Resources and Services Administration recommends screening for 35 genetic and metabolic disorders, and there are an additional 26 secondary disorders that doctors may screen for.

Examples of these metabolic disorders include:

  • phenylketonuria (PKU)
  • congenital adrenal hyperplasia
  • galactosemia
  • biotinidase deficiency

Metabolic disorders may arise if babies do not have the digestive enzymes they need to process food correctly.

Are they genetic?

Yes, metabolic disorders in infants are usually genetic. These complex conditions are rare and inherited, meaning that they run in families.

An error in the baby’s genes means that they do not produce certain necessary digestive enzymes.

Most of these metabolic disorders are autosomal recessive, meaning that the baby requires two copies of an abnormal gene to develop the metabolic disorder.

Babies and infants with metabolic issues may present with a wide range of symptoms depending on the specific disorder.

Infants with metabolic disorders may appear healthy when they are born and then begin to develop symptoms in the following days, weeks, or months. They may also have nonspecific symptoms.

Symptoms may include:

  • lethargy or extreme tiredness
  • fussiness
  • weakness
  • poor feeding
  • fast breathing or short periods without breathing
  • vomiting
  • poor weight gain
  • seizures
  • absence of hair, or alopecia
  • ichthyosis, or dry, thickened, scaly skin
  • enlarged liver, spleen, and kidneys
  • jaundice (yellowing of the skin or eyes)
  • facial irregularities
  • specific odors of the breath or urine

If people notice any of these symptoms in a baby, they should seek medical attention.

Doctors can identify many metabolic disorders through newborn screening (NBS) programs. These screening programs check whether a baby is likely to have a particular condition. This differs from diagnostic testing, which conclusively determines whether an infant has a condition.

All babies born in the U.S. should undergo NBS to check for metabolic problems, as doctors cannot always tell whether they have these issues through a physical examination.

NBS helps detect serious conditions and ensure the baby receives the recommended care and treatment as early as possible. It consists of three parts:

  • blood spot screening to see whether babies have metabolic or other serious health conditions
  • pulse oximetry screening to check for heart conditions
  • hearing screening to see whether a newborn is deaf or has hearing difficulties

Blood spot screening

Doctors may also call this test a heel stick or a 24-hour test. It involves taking a blood sample from the baby between 24 and 48 hours after birth.

It is a simple process and involves a healthcare professional making a quick pinprick on the baby’s heel and collecting blood with special paper.

Once dry, the healthcare professional sends the paper to a laboratory, where the staff runs tests to look for specific conditions. Caregivers usually receive the results in 5–7 days.

Each state has a list of specific tests in its NBS panel. The U.S. government recommends 35 core disorder and 26 secondary disorder screenings, but not every state requires all of these screenings.

Doctors can successfully treat many metabolic disorders, and starting treatment as soon as possible helps prevent serious health risks.

In some cases, infants with metabolic disorders can avoid complications and stay healthy if they follow a special diet and avoid certain foods.

For example, if an infant has PKU, treatment typically involves limiting foods containing phenylalanine. In babies, this may mean drinking special formula that does not contain phenylalanine and following a low-protein diet.

If a baby has galactosemia, doctors may recommend eliminating lactose-containing dairy products from their diet. The baby may need to drink soy-based or another lactose-free formula instead.

Babies with medium-chain acyl-CoA dehydrogenase deficiency cannot convert certain fats to energy. As a result, they may require a special formula.

Other treatments for metabolic disorders may involve taking medications or dietary supplements.

The outlook for infants with inherited metabolic disorders varies depending on the specific condition.

Some metabolic disorders can cause severe health problems or be life threatening. Additionally, some infants with these metabolic disorders have an increased risk of developing neurological problems and learning disabilities.

However, in many cases, doctors can help manage the condition.

Metabolic disorders in infants affect how the infants process food. Often, these disorders run in families.

Newborn babies may have no symptoms of these disorders and gradually over the following days to months become lethargic, fail to gain weight, and have digestive issues.

In the U.S., newborn babies receive screening tests that help to identify metabolic disorders as early as possible. This allows treatment and management to begin early and limits the effects of these conditions.