Browsing Pathways

Hypercholesterolemia, also called elevated cholesterol, is an autosomal dominant disorder caused by a defective LDLR gene. The LDLR gene codes for a receptor that binds to low-density lipoprotein which are carriers of cholesterol in the blood. The mutation on the LDLR gene causes the removal of cholesterol from the bloodstream to be limited, resulting in a buildup of cholesterol in the blood. This disorder is characterized by a large accumulation of cholesterol in the blood. Symptoms of the disorder include angina, tendon xanthomas increased risk of cardiac arrest. Treatment with atorvastatin, simvastatin or rosuvastatin, in combination with a heart healthy diet and regular exercise is very effective. It is estimated that hypercholesterolemia affects 1 in 500 individuals in most countries.

Nonketotic hyperglycinemia (GCE) is a rare inborn error of metabolism (IEM) and autosomal recessive disorder caused by a defective GLDC gene. GLDC encodes for the enzymes involved in the conversion of glycine to CO2, NH3 and hydroxymethyltetrahydrofolic acid. Most patients have abnormally low oxalate excretion in the urine. Other symptoms start presenting in the first few days of life and include lethargy, hypotonia, and myoclonic jerks, and progressing to apnea. GCE often leads to death, and those who regain spontaneous respiration develop intractable seizures and profound mental retardation. Currently there is no cure for Nonketotic hyperglycinemia therefore treatment involves managing symptoms. Frequency for Nonketotic hyperglycinemia has not been documented worldwide.

DOPA-Responsive Dystonia is a condition in which the muscles contract, experience tremors and uncontrolled movements (dystonia). Some cases are mild, while others can be severe. The beginning signs of this condition are dystonia in the legs, and clubfeet. The cause of this condition is usually a mutation in the GCH1 gene, but can sometimes be attributed to mutations in the TH or SPR genes. Tetrahydrobiopterin is an important compound in the production of neurotransmitters, specifically dopamine and serotonin, and the processing of quite a few amino acids, The mutation on GCH1 causes GTP cyclohydrase production to be reduced or absent which causes the first three steps of tetrahydrobiopterin biosynthesis to be compromised. The mutation on the SPR gene affects tetrahydrobiopterin biosynthesis by interfering with the production of sepiapterin reductase, which is needed to complete the final step of tetrahydrobiopterin biosynthesis. The TH gene mutation also affects dopamine production through the decreased function of an enzyme called tyrosine hydroxylase, which is responsible for converting tyrosine to dopamine. Dopamine is imperative in maintaining smooth muscle movements, which is why patients with DOPA-responive dystonia experience tremors and movement problems.

Hyperphenylalaninemia is the high presence of phenylalanine in the system/blood caused by a genetic mutation. In this case a missense error in the gene which encodes GTP cyclohydrolase. Consequently, this form of hyperphenylalaninemia is also called GTP cyclohydrolase I deficiency and/or dopa-responsive dystonia. It is an autosomal recessive mutation. The mutation results in a reduction in the production of BH4 which is a necessary component in the reaction which transforms phenylalanine to other products in the body. Common symptoms include: abnormality of eye mpvement, choreoathetosis, dysphagia, dystonia, excessive salivation, hypekinesis, lethargy, limb hyptertonia, seizures, tremor, among others.

BH4-deficient hyperphenylalaninemia has several causes. One such cause is a PTS deficiency resultant from a genetic mutation. (In particular, a mutation in the gene encoding 6-pyruvoyl-tetrahydropterin synthase.) The mutation is autosomal recessive. Common symptoms include: muscular hypotonia, ataxia, bradykinesia, choreoathetosis, depressivity, dysphagia, hyperkinesis, hypsarrhythmia, myoclonus, and others. BH4 is a cofactor involved in many things and associated with neurotransmitter synthesis. In short, the reduction of levels of BH4 creates issues in the metabolism of phenylalanine. This cascade of reactions produces the aforementioned symptoms.

Hyperphenylalaninemia due to dihydropteridine reductase deficiency (DHPR) is the high presence of phenylalanine in the system/blood caused by a genetic mutation. More specificially, mutations in the QDPR gene are the root cause of the condition. One observes that such a mutation results in an error encoding a reductase enzyme, and from there a chain reaction of effects lead to the observed effects of the disease. The mutation is autosomal recessive. When tetrahydrobiopterin levels drop, the breakdown of many several amino acids, such as phenylalanine, is reduced and as a result their levels in the blood augment. Symptoms of hyperphenylalaninemia due to dihydropteridine reductase deficiency include: dysphagia, global development delay, microcephaly, and intellectual disability (among others). Treatment consists of BH4 supplements as well as other medical treatments.

Segawa syndrome is a condition in which the affected individual has a clumsy or unusual gait, and experiences involuntary muscle contractions and uncontrolled movements (dystonia). Some cases are mild, while others can be severe. The beginning signs of this condition are dystonia in the legs, and clubfeet. The cause of this condition is a mutation in the GCH1 gene. Tetrahydrobiopterin is an important compound in the production of neurotransmitters, specifically dopamine and serotonin, and the processing of quite a few amino acids, The mutation on GCH1 causes GTP cyclohydrase 1 production to be reduced or absent which causes the first three steps of tetrahydrobiopterin biosynthesis to be compromised. Dopamine is imperative in maintaining smooth muscle movements, which is why patients with Segawa syndrome experience movement problems and an unusual gait.

Sepiapterin reductase deficiency results from a metabolic disorder; namely, the underproduction of Sepiapterin. The cause of this underproduction is an autosomal recessive genetic mutation in the SPR gene. This gene is responsible for Sepiapterin production, and naturally, when the gene malfunctions the production of this metabolite is altered leading to a range of effects on the body. In this case, some symptoms of Sepiapterin Deficiency are: motor and speech delay, axial hypotonia, dystonia, weakenss microcephaly, dysarthria, autonomic dysfunction, oculogyric crises, drowsiness, among others.

Carnosinemia, also known as carnosinemia, is a rare inborn error of metabolism (IEM) and recessive autosomal disorder caused by a defective CNDP1 gene which encodes for carnosinase. Carnosinase is a dipeptidase enzyme that catalyzes the breakdown of Carnosine into alanine and histidine. This disorder is characterized by secretion of large amounts of carnosine and anserine in the urine but low levels of methylhistidine. Patients also have unusually high concentrations of homocarnosine in the cerebrospinal fluid. Other symptoms include progressive neurologic disorders characterized by severe mental defect and myoclonic seizures. There is no known cure for Carnosinemia therefore treatment involves management of symptoms. There have been about 30 cases of Carnosinemia reported worldwide.

A transient defect in tyrosine metabolism is a common aminoacidopathy in the premature and full-term human infant. This disorder, termed neonatal tyrosinemia, was first described by Levine and Gordon in 1939. In the intervening years other workers have studied this disorder, and have noted the concurrence of tyrosinemia and tyrosyluria. In a current survey of 15,000 infants, 6 mild tyrosinemia occurred during the first week of life in 10% of full-term infants, and severe tyrosinemia occurred in approximately 30% of premature infants. The enzymatic basis of neonatal tyrosinemia is complex and involves the susceptibility of p-hydroxyphenylpyruvic acid oxidase to inhibition in the presence of its substrate, p-hydroxyphenylpyruvic acid and derivatives. The inhibition is reversible by removal of excess substrate and by reducing agents such as ascorbic acid, 2, 6-dichiorophenolindophenol, and a number of hydroquinone and phenylenediamine compounds.