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Glutathione synthetase deficiency (GSD) is a rare
autosomal An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...
recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
metabolic disorder A metabolic disorder is a disorder that negatively alters the body's processing and distribution of macronutrients, such as proteins, fats, and carbohydrates. Metabolic disorders can happen when abnormal chemical reactions in the body alter the ...
that prevents the production of
glutathione Glutathione (GSH, ) is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, pero ...
. Glutathione helps prevent damage to cells by neutralizing harmful molecules generated during energy production. Glutathione also plays a role in processing medications and cancer-causing compounds (
carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substan ...
s), and building DNA, proteins, and other important cellular components.


Genetics

Mutations in the ''GSS'' gene cause glutathione synthetase deficiency. This gene provides instructions for making the
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
glutathione synthetase Glutathione synthetase (GSS) () is the second enzyme in the glutathione (GSH) biosynthesis pathway. It catalyses the condensation of gamma-glutamylcysteine and glycine, to form glutathione. Glutathione synthetase is also a potent antioxidant ...
. This enzyme is involved in a process called the gamma-glutamyl cycle, which takes place in most of the body's cells. This cycle is necessary for producing a molecule called glutathione. Glutathione protects cells from damage caused by unstable oxygen-containing molecules, which are byproducts of energy production. Glutathione is called an
antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...
because of its role in protecting cells from the damaging effects of these unstable molecules which are byproducts of energy production. Mutations in the ''GSS'' gene prevent cells from making adequate levels of glutathione, leading to the signs and symptoms of glutathione synthetase deficiency. This disorder is inherited in an autosomal recessive pattern, which means the defective gene is located on an
autosome An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...
, and two copies of the gene - one from each parent - are required to be born with the disorder. The parents of an individual with an autosomal recessive disorder each carry one copy of the defective gene, but usually are not affected by the disorder.


Diagnosis

Glutathione synthetase deficiency can be classified into three types: mild, moderate and severe. * ''Mild'' glutathione synthetase deficiency usually results in the destruction of red blood cells (
hemolytic anemia Hemolytic anemia or haemolytic anaemia is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells (RBCs), either in the blood vessels (intravascular hemolysis) or elsewhere in the human body (extravascular). This most commonly ...
). Rarely, affected people also excrete large amounts of a compound called 5-oxoproline (also called pyroglutamic acid, or pyroglutamate) in their urine (5-oxoprolinuria). This compound builds up when glutathione is not processed correctly in cells. * Individuals with ''moderate'' glutathione synthetase deficiency may experience symptoms beginning shortly after birth including hemolytic anemia, 5-oxoprolinuria, and elevated acidity in the blood and tissues (
metabolic acidosis Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys ...
). * In addition to the features present in moderate glutathione synthetase deficiency, individuals affected by the ''severe'' form of this disorder may experience neurological symptoms. These problems may include
seizure An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with los ...
s; a generalized slowing down of physical reactions, movements, and speech (
psychomotor retardation Psychomotor may refer to: * Psychomotor learning, the relationship between cognitive functions and physical movement * Psychomotor retardation, a slowing-down of thought and a reduction of physical movements in an individual * Psychomotor agitatio ...
);
intellectual disability Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation,Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by signifi ...
; and a loss of coordination (
ataxia Ataxia is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in eye movements. Ataxia is a clinical manifestation indicating dysfunction of ...
). Some people with severe glutathione synthetase deficiency also develop recurrent bacterial infections.


Treatment

As of 2018, there is no cure for GSD, and treatment is restricted to manage symptoms and associated problems. Thus,
sodium bicarbonate Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation ( Na+) and a bicarbonate anion ( HCO3−) ...
is recommended to treat
metabolic acidosis Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys ...
, and antioxidants, among them vitamins E and C, can reduce oxidative damage.


References


Further reading

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External links

{{Medical resources , DiseasesDB = 29839 , ICD10 = , ICD9 = , ICDO = , OMIM = 266130 , MedlinePlus = , eMedicineSubj = ped , eMedicineTopic = 867 , MeshID = C536835 , Orphanet = 32 , SNOMED CT = 234589002 Amino acid metabolism disorders Autosomal recessive disorders Rare diseases Disorders causing seizures Intellectual disability