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Isovaleric acidemia
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Isovaleric acidemia

Isovaleric acidemia is a rare organic acid disorder that prevents the body from properly breaking down the amino acid leucine, leading to a toxic buildup of organic acids.

Overview

Isovaleric acidemia is an inherited disorder where the body cannot break down the protein building block leucine. It is classified as an organic acid disorder, which causes an abnormal buildup of organic acids in the blood, urine, and tissues. This accumulation can be toxic and lead to serious health complications.

Symptoms

Health problems range from mild to life-threatening. In severe cases, symptoms appear shortly after birth and include:

  • Poor feeding
  • Vomiting
  • Lack of energy (lethargy)
  • Seizures
  • Coma
  • A distinctive odor of "sweaty feet" during acute illness

In milder cases, symptoms may appear during childhood, characterized by failure to gain weight (failure to thrive) and delayed development. Episodes can be triggered by fasting, infections, or high-protein intake. Some individuals with the gene mutation remain asymptomatic.

Causes

The condition is caused by mutations in the IVD gene, which provides instructions for making an enzyme that processes leucine. When this enzyme is deficient, isovaleric acid and related compounds build up to harmful levels, damaging the brain and nervous system.

Inheritance

Isovaleric acidemia is inherited in an autosomal recessive pattern. Both copies of the IVD gene in each cell must have mutations for the condition to occur. Parents of an affected individual are typically carriers who do not exhibit symptoms.

Frequently Asked Questions

Individuals with isovaleric acidemia must strictly limit their intake of natural protein, particularly leucine, which is found in meat, dairy, eggs, and legumes. Instead, they rely on a specialized medical formula that provides all necessary amino acids except leucine, along with carbohydrates and fats for energy. The specific protein allowance is determined by a metabolic dietitian based on the individual's age, growth rate, and metabolic stability. Adhering to this diet is essential to prevent the toxic buildup of organic acids that can damage the brain and nervous system.
Metabolic crises are most commonly triggered by physiological stressors that increase the body's need for energy, such as infections, fevers, fasting, or surgery. During these times, the body breaks down its own proteins for fuel, releasing more leucine and overwhelming the deficient enzyme system. To prevent crises, parents must ensure the child eats regularly and does not fast. During illness, it is critical to increase carbohydrate intake and provide intravenous fluids if oral intake is poor. Close monitoring of blood glucose and ketone levels during any illness is vital to catch early signs of metabolic decompensation.
The "sweaty feet" smell is caused by the buildup of isovaleric acid, a toxic byproduct that accumulates when the body cannot break down the amino acid leucine. This odor is often most noticeable during acute metabolic crises triggered by illness, fasting, or high-protein intake. For caregivers, detecting this smell is a crucial early warning sign that the body is under metabolic stress. It should prompt immediate medical attention and the initiation of crisis protocols, such as stopping protein intake and providing high-calorie carbohydrates, to prevent severe complications like seizures or coma.
Yes, isovaleric acidemia is included in standard newborn screening panels in many regions. The test measures levels of isovalerylcarnitine in the blood. A positive result indicates a high likelihood of the condition, but it is not a definitive diagnosis. It must be confirmed with further genetic testing for mutations in the IVD gene and additional biochemical tests. Early detection through newborn screening is crucial because it allows for the immediate start of dietary management and monitoring, which can significantly improve long-term neurological outcomes and prevent life-threatening crises.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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