Ethylmalonic encephalopathy
Encyclopedia
Ethylmalonic encephalopathy is a rare autosomal
recessive genetic disorder
defined as an inborn error of metabolism
, in detail a failure to detoxify hydrogen sulfide
in mitochondria which results normally from cysteine
degradation. It affects several body systems, including the gastrointestinal system, circulatory system
, and particularly the nervous system
.
), 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.
Mutations in the ETHE1 gene cause ethylmalonic encephalopathy. The ETHE1 gene makes 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 its exact function, however.
Mutations in the ETHE1 gene lead to the production of a defective version of the enzyme or prevents the enzyme from being made. A lack of the ETHE1 enzyme impairs the 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 an autosomal recessive disorder, which means the defective gene is located on an autosome
, and both parents must carry one copy of the defective gene in order to have a child born with the disorder. The parents of a child with an autosomal recessive disorder are usually not affected by the disorder.
Autosome
An autosome is a chromosome that is not a sex chromosome, or allosome; that is to say, there is an equal number of copies of the chromosome in males and females. For example, in humans, there are 22 pairs of autosomes. In addition to autosomes, there are sex chromosomes, to be specific: X and Y...
recessive genetic disorder
Genetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....
defined as an inborn error of metabolism
Inborn error of metabolism
Inborn errors of metabolism comprise a large class of genetic diseases involving disorders of metabolism. The majority are due to defects of single genes that code for enzymes that facilitate conversion of various substances into others...
, in detail a failure to detoxify hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
in mitochondria which results normally from cysteine
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
degradation. It affects several body systems, including the gastrointestinal system, circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
, and particularly the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
.
Symptoms
Neurologic signs and symptoms include progressively delayed development, weak muscle tone (hypotoniaHypotonia
Hypotonia is a state of low muscle tone , often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases and disorders that affect motor nerve control by the brain or muscle strength...
), 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
Acrocyanosis
Acrocyanosis is persistent blue or cyanotic discoloration of the extremities, most commonly occurring in the hands, although it also occurs in the feet and distal parts of face....
). 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 lead to the production of a defective version of the enzyme or prevents the enzyme from being made. A lack of the ETHE1 enzyme impairs the 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 an autosomal recessive disorder, which means the defective gene is located on an autosome
Autosome
An autosome is a chromosome that is not a sex chromosome, or allosome; that is to say, there is an equal number of copies of the chromosome in males and females. For example, in humans, there are 22 pairs of autosomes. In addition to autosomes, there are sex chromosomes, to be specific: X and Y...
, and both parents must carry one copy of the defective gene in order to have a child born with the disorder. The parents of a child with an autosomal recessive disorder are usually not affected by the disorder.