Isovaleric acidemia (IVA) occurs when the body cannot breakdown certain parts of the proteins found in food. This can cause a build-up of toxic substances which can lead to bouts of serious illness known as metabolic crises. There are two types of IVA. The acute, neonatal type has more severe symptoms. In the chronic, intermittent type symptoms can come and go. Symptoms include poor feeding, tremor, vomiting, low muscle tone, and lack of energy (lethargy). One characteristic sign of IVA is an odor of sweaty feet during illness. IVA occurs due to variants in the IVD gene and is inherited in an autosomal recessive pattern. Diagnosis of IVD is based on the symptoms, clinical exam, and blood and urine testing. The results of genetic testing may help confirm the diagnosis.