2-methylbutyryl-CoA dehydrogenase deficiency

2-methylbutyryl-CoA dehydrogenase deficiency is a type of organic acid disorder in which the body is unable to process proteins properly. Organic acid disorders lead to an abnormal buildup of particular acids known as organic acids. Abnormal levels of organic acids in the blood (organic acidemia), urine (organic aciduria), and tissues can be toxic and can cause serious health problems.

Normally, the body breaks down proteins from food into smaller parts called amino acids. Amino acids can be further processed to provide energy for growth and development. People with 2-methylbutyryl-CoA dehydrogenase deficiency have inadequate levels of an enzyme that helps process a particular amino acid called isoleucine.

Health problems related to 2-methylbutyryl-CoA dehydrogenase deficiency vary widely from severe and life-threatening to mild or absent. Signs and symptoms of this disorder can begin a few days after birth or later in childhood. The initial symptoms often include poor feeding, lack of energy (lethargy), vomiting, and an irritable mood. These symptoms sometimes progress to serious medical problems such as difficulty breathing, seizures, and coma. Additional problems can include poor growth, vision problems, learning disabilities, muscle weakness, and delays in motor skills such as standing and walking.

Symptoms of 2-methylbutyryl-CoA dehydrogenase deficiency may be triggered by prolonged periods without food (fasting), infections, or eating an increased amount of protein-rich foods. Some people with this disorder never have any signs or symptoms (asymptomatic). For example, individuals of Hmong ancestry identified with 2-methylbutyryl-CoA dehydrogenase deficiency through newborn screening are usually asymptomatic.

2-methylbutyryl-CoA dehydrogenase deficiency is a rare disorder; its actual incidence is unknown. This disorder is more common, however, among Hmong populations in southeast Asia and in Hmong Americans. 2-methylbutyryl-CoA dehydrogenase deficiency occurs in 1 in 250 to 1 in 500 people of Hmong ancestry.

Mutations in the ACADSB gene cause 2-methylbutyryl-CoA dehydrogenase deficiency.

The ACADSB gene provides instructions for making an enzyme called 2-methylbutyryl-CoA dehydrogenase that helps process the amino acid isoleucine. Mutations in the ACADSB gene reduce or eliminate the activity of this enzyme. With a shortage (deficiency) of 2-methylbutyryl-CoA dehydrogenase, the body is unable to break down isoleucine properly. As a result, isoleucine is not converted to energy, which can lead to characteristic features of this disorder, such as lethargy and muscle weakness. Also, an organic acid called 2-methylbutyrylglycine and related compounds may build up to harmful levels, causing serious health problems.

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

These resources address the diagnosis or management of 2-methylbutyryl-CoA dehydrogenase deficiency:

These resources from MedlinePlus offer information about the diagnosis and management of various health conditions:

  • 2-MBADD
  • 2-MBCD deficiency
  • 2-MBG
  • 2-methylbutyryl-coenzyme A dehydrogenase deficiency
  • 2-methylbutyryl glycinuria
  • short/branched-chain acyl-CoA dehydrogenase deficiency