Acyl-CoA oxidase deficiency | |
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Other names | ACOX1 deficiency |
Acyl CoA oxidase enzyme | |
Specialty | Medical genetics |
Acyl-CoA oxidase deficiency is a rare disorder that leads to significant damage and deterioration of nervous system functions (neurodegeneration). [1] It is caused by pathogenic variants in ACOX1 , which codes for the production of an enzyme called peroxisomal straight-chain acyl-CoA oxidase (ACOX1). [1] This specific enzyme is responsible for the breakdown of very long chain fatty acids (VLCFAs). [2]
Defective function of the ACOX1 enzyme prevents proper breakdown of these VLCFAs, leading to accumulation and interference with the nervous system. [1] [2] Acyl-CoA oxidase deficiency affects a person from birth, and most newborns affected with this condition will not survive past early childhood. [1] Affected individuals can be born with hypotonia, seizures, and dysmorphic features, such as widely spaced eyes, a low nasal bridge and low set ears. Polydactyly and hepatomegaly have also been described. [1] Most babies will learn to walk and begin speaking, before experiencing a rapid decline in motor function between the ages of 1 and 3. [3] As the person ages, and the conditions worsens, they begin to experience exaggerated reflexes (hyperreflexia), more severe and frequent seizures, and gradual loss of vision and hearing. [1] [2] There is no cure for this condition, however there are a range of symptom-based treatments, used to provide supportive care.
Children are born with this condition and their symptoms can be seen immediately. [2] In the early stages these can appear quite mild; weak muscle tone (often extreme hypotonia), lack of neonatal reflexes, seizures and abnormal (dysmorphic) facial features such as widely spaced eyes, a low nasal bridge, low set ears and an abnormally large forehead. [1] [2] Due to the nature of the disease, in the build-up of VLCFAs, symptoms worsen progressively over time. [4] Children can often reach the stage at which they begin to walk and talk, before experiencing a rapid decline in motor skills due to demyelination and subsequent nerve damage. [2] [3] A hearing deficit may develop, eyesight and response to visual and physical stimuli begins to diminish and eventually becomes non-existent. [1] [2] The life expectancy of an individual with ACOX1 deficiency is 5 years. [2] [3]
Acyl-CoA oxidase deficiency is an autosomal recessive disorder that is caused by biallelic pathogenic variants in ACOX1. [1] [5] This is the gene that codes for the production of an enzyme called peroxisomal straight-chain acyl-CoA oxidase which is responsible for the breakdown of VLCFAs. [1] [2] It is not completely clear how the build-up of these VLCFAs causes the symptoms seen with this condition, however research suggests that this abnormal accumulation triggers an inflammation in the nervous system which leads to demyelination. [1] Demyelination leads to the loss of white matter, leukodystrophy, in the brain and spinal cord. [1] [5] It is this leukodystrophy that is related to the development of neurological abnormalities in people with Acyl-CoA oxidase deficiency. [5] Acyl-CoA oxidase deficiency is an extremely rare condition. [1]
Diagnosis can be done both prenatally based on family history and after birth based on clinical suspicion. [1] [5] The primary prenatal diagnosis techniques involve the assessment of amniotic fluid for an abnormal elevation in VLCFAs, and a reduced presence (or in some cases complete absence) of acyl-CoA oxidase in fibroblasts. If the causative variants in a family are known, prenatal diagnosis can be performed by molecular testing. [4] After birth, there are a number of diagnostic techniques available for use. A blood sample can be taken, from which the serum levels of VLCFAs and acyl-CoA oxidase activity can be assessed. Analysis of VLCFAs is important for the identification of ACOX1 deficiency, if a leukodystrophy has been identified [5] Since the condition is genetic, and is caused by pathogenic variants in ACOX1, it can be confirmed by sequence or copy number analysis. [1] Due to the rarity of this condition, people who have it may not be diagnosed early in their disease progression. As a result, acyl-CoA oxidase deficiency may be misdiagnosed as similar conditions such as Usher syndrome and neonatal adrenoleukodystrophy. [5] [6]
There are no cures for ACOX1 deficiency, supportive care is used to manage specific clinical symptoms for affected individuals. [1] Treatment is based upon symptoms, with the aim the provide some relief. [5] Pharmacologic agents are used to help improve muscle tone (management of dystonia) and to block neurological signalling to the muscle. Physical therapy is used to improve movement and function. [5] For the specific treatment of recurrent seizures, there are both pharmaceutical and surgical options. [5]
Adrenoleukodystrophy (ALD) is a disease linked to the X chromosome. It is a result of fatty acid buildup caused by failure of peroxisomal fatty acid beta oxidation which results in the accumulation of very long chain fatty acids in tissues throughout the body. The most severely affected tissues are the myelin in the central nervous system, the adrenal cortex, and the Leydig cells in the testes. The long chain fatty acid buildup causes damage to the myelin sheath of the neurons of the brain, resulting in seizures and hyperactivity. Other symptoms include problems in speaking, listening, and understanding verbal instructions.
Macrocephaly is a condition in which circumference of the human head is abnormally large. It may be pathological or harmless, and can be a familial genetic characteristic. People diagnosed with macrocephaly will receive further medical tests to determine whether the syndrome is accompanied by particular disorders. Those with benign or familial macrocephaly are considered to have megalencephaly.
Kernicterus is a bilirubin-induced brain dysfunction. The term was coined in 1904 by Christian Georg Schmorl. Bilirubin is a naturally occurring substance in the body of humans and many other animals, but it is neurotoxic when its concentration in the blood is too high, a condition known as hyperbilirubinemia. Hyperbilirubinemia may cause bilirubin to accumulate in the grey matter of the central nervous system, potentially causing irreversible neurological damage. Depending on the level of exposure, the effects range from clinically unnoticeable to severe brain damage and even death.
Methylmalonic acidemias, also called methylmalonic acidurias, are a group of inherited metabolic disorders, that prevent the body from properly breaking down proteins and fats. This leads to a buildup of a toxic level of methylmalonic acid in body liquids and tissues. Due to the disturbed branched-chain amino acids (BCAA) metabolism, they are among the classical organic acidemias.
Alexander disease is a very rare autosomal dominant leukodystrophy, which are neurological conditions caused by anomalies in the myelin which protects nerve fibers in the brain. The most common type is the infantile form that usually begins during the first two years of life. Symptoms include mental and physical developmental delays, followed by the loss of developmental milestones, an abnormal increase in head size and seizures. The juvenile form of Alexander disease has an onset between the ages of 2 and 13 years. These children may have excessive vomiting, difficulty swallowing and speaking, poor coordination, and loss of motor control. Adult-onset forms of Alexander disease are less common. The symptoms sometimes mimic those of Parkinson's disease or multiple sclerosis, or may present primarily as a psychiatric disorder.
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. Hypotonia is a lack of resistance to passive movement, whereas muscle weakness results in impaired active movement. Central hypotonia originates from the central nervous system, while peripheral hypotonia is related to problems within the spinal cord, peripheral nerves and/or skeletal muscles. Severe hypotonia in infancy is commonly known as floppy baby syndrome. Recognizing hypotonia, even in early infancy, is usually relatively straightforward, but diagnosing the underlying cause can be difficult and often unsuccessful. The long-term effects of hypotonia on a child's development and later life depend primarily on the severity of the muscle weakness and the nature of the cause. Some disorders have a specific treatment but the principal treatment for most hypotonia of idiopathic or neurologic cause is physical therapy and/or occupational therapy for remediation.
Zellweger syndrome is a rare congenital disorder characterized by the reduction or absence of functional peroxisomes in the cells of an individual. It is one of a family of disorders called Zellweger spectrum disorders which are leukodystrophies. Zellweger syndrome is named after Hans Zellweger (1909–1990), a Swiss-American pediatrician, a professor of pediatrics and genetics at the University of Iowa who researched this disorder.
Krabbe disease (KD) is a rare and often fatal lysosomal storage disease that results in progressive damage to the nervous system. KD involves dysfunctional metabolism of sphingolipids and is inherited in an autosomal recessive pattern. The disease is named after the Danish neurologist Knud Krabbe (1885–1961).
Leukodystrophies are a group of, usually, inherited disorders, characterized by degeneration of the white matter in the brain. The word leukodystrophy comes from the Greek roots leuko, "white", dys, "abnormal" and troph, "growth". The leukodystrophies are caused by imperfect growth or development of the glial cells which produce the myelin sheath, the fatty insulating covering around nerve fibers. Leukodystrophies may be classified as hypomyelinating or demyelinating diseases, respectively, depending on whether the damage is present before birth or occurs after. While all leukodystrophies are the result of genetic mutations, other demyelinating disorders have an autoimmune, infectious, or metabolic etiology.
Mitochondrial trifunctional protein deficiency is an autosomal recessive fatty acid oxidation disorder that prevents the body from converting certain fats to energy, particularly during periods without food. People with this disorder have inadequate levels of an enzyme that breaks down a certain group of fats called long-chain fatty acids.
Very long-chain acyl-coenzyme A dehydrogenase deficiency is a fatty-acid metabolism disorder which prevents the body from converting certain fats to energy, particularly during periods without food.
Biotinidase deficiency is an autosomal recessive metabolic disorder in which biotin is not released from proteins in the diet during digestion or from normal protein turnover in the cell. This situation results in biotin deficiency.
D-Bifunctional protein deficiency is an autosomal recessive peroxisomal fatty acid oxidation disorder. Peroxisomal disorders are usually caused by a combination of peroxisomal assembly defects or by deficiencies of specific peroxisomal enzymes. The peroxisome is an organelle in the cell similar to the lysosome that functions to detoxify the cell. Peroxisomes contain many different enzymes, such as catalase, and their main function is to neutralize free radicals and detoxify drugs. For this reason peroxisomes are ubiquitous in the liver and kidney. D-BP deficiency is the most severe peroxisomal disorder, often resembling Zellweger syndrome.
Guanidinoacetate methyltransferase deficiency is an autosomal recessive cerebral creatine deficiency that primarily affects the nervous system and muscles. It is the first described disorder of creatine metabolism, and results from deficient activity of guanidinoacetate methyltransferase, an enzyme involved in the synthesis of creatine. Clinically, affected individuals often present with hypotonia, seizures and developmental delay. Diagnosis can be suspected on clinical findings, and confirmed by specific biochemical tests, brain magnetic resonance spectroscopy, or genetic testing. Biallelic pathogenic variants in GAMT are the underlying cause of the disorder. After GAMT deficiency is diagnosed, it can be treated by dietary adjustments, including supplementation with creatine. Treatment is highly effective if started early in life. If treatment is started late, it cannot reverse brain damage which has already taken place.
Megalencephalic leukoencephalopathy with subcortical cysts is a form of hereditary CNS demyelinating disease. It belongs to a group of disorders called leukodystrophies. It is characterized by early-onset enlargement of the head (macrocephaly) as well as delayed-onset neurological deterioration to include spasticity, epilepsy, and lack of muscular coordination. MLC does not appear to be a disease that is fatal at birth or early in life despite its symptoms, although the number of patients throughout history known to have the disease is fairly limited.
Transient hyperammonemia of the newborn (THAN) is an idiopathic disorder occasionally present in preterm newborns but not always symptomatic. Continuous dialysis or hemofiltration have proven to be the most effective treatment. Nutritional support and sodium benzoate have also been used to treat THAN.
Sepiapterin reductase deficiency is an inherited pediatric disorder characterized by movement problems, and most commonly displayed as a pattern of involuntary sustained muscle contractions known as dystonia. Symptoms are usually present within the first year of age, but diagnosis is delayed due to physicians lack of awareness and the specialized diagnostic procedures. Individuals with this disorder also have delayed motor skills development including sitting, crawling, and need assistance when walking. Additional symptoms of this disorder include intellectual disability, excessive sleeping, mood swings, and an abnormally small head size. SR deficiency is a very rare condition. The first case was diagnosed in 2001, and since then there have been approximately 30 reported cases. At this time, the condition seems to be treatable, but the lack of overall awareness and the need for a series of atypical procedures used to diagnose this condition pose a dilemma.
NGLY1 deficiency is a very rare genetic disorder caused by biallelic pathogenic variants in NGLY1. It is an autosomal recessive disorder. Errors in deglycosylation are responsible for the symptoms of this condition. Clinically, most affected individuals display developmental delay, lack of tears, elevated liver transaminases and a movement disorder. NGLY1 deficiency is difficult to diagnose, and most individuals have been identified by exome sequencing.
CDKL5 deficiency disorder (CDD) is a rare genetic disorder caused by pathogenic variants in the gene CDKL5.
Salt and pepper developmental regression syndrome, also known as Amish infantile epileptic syndrome or GM3 deficiency syndrome, is a rare autosomal recessive progressive neurological disorder characterized by developmental delay, severe intellectual disability, seizures, and skin pigmentation irregularities. The clinical symptoms of this condition start manifesting soon after birth, during the newborn/neo-natal stage of life.
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