Ethylmalonic encephalopathy

Ethylmalonic encephalopathy is an inherited disorder that affects several body systems, particularly the nervous system.

Symptoms
Neurologic signs and symptoms include progressively delayed development, weak muscle tone (hypotonia), seizures, and abnormal movements. The body's network of blood vessels is also affected. Children with this disorder may experience rashes of tiny red spots (petechiae) caused by bleeding under the skin and blue discoloration in the hands and feet due to reduced oxygen in the blood (acrocyanosis). Chronic diarrhea is another common feature of ethylmalonic encephalopathy.

The signs and symptoms of ethylmalonic encephalopathy are apparent at birth or begin in the first few months of life. Problems with the nervous system typically worsen over time, and most affected individuals survive only into early childhood. A few children with a milder, chronic form of this disorder have been reported.

Pathophysiology
Mutations in the ETHE1 gene cause ethylmalonic encephalopathy. The ETHE1 gene provides instructions for making an enzyme that plays an important role in energy production. It is active in mitochondria, which are the energy-producing centers within cells. Little is known about the enzyme's exact function, however.

Mutations in the ETHE1 gene lead to the production of a nonfunctional version of the enzyme or prevent any enzyme from being made. A lack of the ETHE1 enzyme impairs the body's ability to make energy in mitochondria. Additionally, a loss of this enzyme allows potentially toxic compounds, including ethylmalonic acid and lactic acid, to build up in the body. Excess amounts of these compounds can be detected in urine. It remains unclear how a loss of the ETHE1 enzyme leads to progressive brain dysfunction and the other features of ethylmalonic encephalopathy.

This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered.