Definition

Metabolic disorders in infants affect how babies digest certain nutrients such as carbohydrates, fats, or proteins and convert these nutrients into fuel for their bodies. Metabolism is the complex process by which cells convert food into chemical compounds for energy.

Metabolic disorders occur when there is an abnormal chemical reaction that disrupts the breakdown or storage of nutrients in the body. Most metabolic disorders in infants are genetic conditions or result from genetic mutations. Therefore, these disorders are rare, occurring in about 1 in 2500 births.

In healthy infants, enzymes in the digestive tract break down nutrients from breast milk or formula into glucose, fats, and amino acids. These digested nutrients can be used immediately as energy or stored for later use.

When a metabolic disorder occurs, it can lead to nutrient imbalances that cause health problems. If not properly managed, some of these conditions can have serious consequences for growth and development, and may even be life-threatening. However, symptoms can vary widely depending on the specific disorder and its severity.

Causes

Metabolic disorders in infants are generally rare and genetic, meaning these diseases are mostly inherited within families. Most of these disorders are autosomal recessive, where the infant inherits two copies of an abnormal gene from each parent, resulting in a metabolic disorder.

Genetic mutations prevent the infant from producing certain enzymes needed for nutrient digestion. Metabolic disorders can disrupt the metabolism of carbohydrates, proteins, fatty acids, or glucose storage.

Here are some examples of metabolic disorders in infants:

• Phenylketonuria (PKU)

A rare genetic condition caused by mutations in the PAH (phenylalanine hydroxylase) gene. This gene helps produce an enzyme needed to break down the amino acid phenylalanine. PKU causes phenylalanine to accumulate in the body, potentially leading to growth and developmental issues if untreated.

• Congenital Adrenal Hyperplasia (CAH)

A group of inherited disorders affecting the adrenal glands above the kidneys. These disorders prevent the adrenal glands from producing certain hormones, potentially affecting puberty.

• Galactosemia

A disorder that impairs the body's ability to process galactose, a simple sugar found in many foods. Galactose is part of lactose found in many dairy products, breast milk, and baby formula. This condition causes galactose to accumulate in the body.

• Maple Syrup Urine Disease (MSUD)

A condition that hinders the proper processing of amino acids in proteins, characterized by the sweet-smelling urine resembling maple syrup. Without treatment, it can lead to developmental delays and other health issues.

• Familial Hypercholesterolemia

A genetic disorder affecting the body's ability to process cholesterol, leading to high levels of "bad" LDL cholesterol in the blood.

• Urea Cycle Disorders

Metabolic disorders resulting from enzyme deficiencies in the process of removing ammonia from the blood, causing ammonia buildup.

Risk Factor

Genetic factors, such as a family history of early-onset metabolic disorders, can increase a child's risk of similar issues. Environmental factors, microbiomes (microorganisms living in our bodies), or epigenetics can also contribute to metabolic disorders in infants.

Symptoms

Symptoms of metabolic disorders in infants can vary widely. A baby may appear healthy at birth but start showing symptoms after days, weeks, or even years (rarely). Common symptoms of metabolic disorders include:

• Abnormal odor from the baby's breath, sweat, or urine
• Excessive sleepiness (somnolence) compared to other infants
• Lethargy or extreme weakness
• Difficulty or refusal to nurse
• Rapid or labored breathing
• Vomiting after feeding
• Poor weight gain
• Yellowing of the skin or whites of the eyes (jaundice)
• Seizures
• Thin or absent hair
• Dry, thick, or scaly skin
• Enlarged internal organs such as the liver, spleen, or kidneys
• Abnormal heart rates (fast or slow)

Diagnosis

Metabolic disorders in infants are typically diagnosed after birth. Doctors perform newborn screenings, including tests for several metabolic disorders, to enable early treatment.

Diagnosis involves:

• Asking about the parents' medical history
• Family history of diseases
• Any complications during pregnancy
• Routine lifestyle

A physical examination of the baby is conducted to assess clinical conditions. If there is a history or symptoms indicative of a metabolic disorder, additional tests such as blood and urine laboratory tests will be performed.

Management

Treatment for metabolic disorders in infants depends on the specific disorder. The goal is to treat and reduce complications. Generally, treatment includes:

• Avoiding foods that cannot be digested due to enzyme deficiencies
• Using specific baby formulas as recommended
• Providing medications and supplements to alleviate symptoms
• Ensuring adequate fluid intake to prevent dehydration

Complications

Metabolic disorders that affect nutrient digestion can cause conditions such as:

• Hypoglycemia: Abnormally low blood sugar levels.
• Hyperammonemia: Accumulation of ammonia in the body due to impaired waste elimination.
• Acidosis: Excessive acid in body fluids due to fatty acid oxidation disorders.
• Developmental delays
• Failure to thrive

Prevention

Preventing metabolic disorders is challenging because most of these conditions are genetic or inherited from both parents. Couples with a family history of inherited disorders should consider genetic counseling or screening when planning a pregnancy or during pregnancy to discuss potential risks.

Experts also recommend mandatory newborn screening for metabolic disorders to help parents manage these conditions early, improving the quality of life for both the baby and the parents.

When to See a Doctor?

If you have a family history of metabolic disorders and are planning a pregnancy, consult a doctor. Genetic screening can help anticipate potential risks. If your baby shows any symptoms mentioned above, seek medical attention promptly for proper diagnosis and treatment.

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