Browsing Pathways

Hypermethioninemia is a rare error of metabolism (IEM) which arises when there is a disfunction in the gene called AHCY. This gene is responsible for Adenosylhomocysteinase, an enzyme which takes S-adenosyl homocysteine as input, and produces homocysteine as its output. This outputted compound through the its respective pathway may be turned back into cysteine methionine. A dysfunctional defect Adenosylhomocysteinase can lead to the build of of these two compounds in the blood. Of particular interest is that individuals who are affected by hypermethioninemia present a wide spectrum of symptoms. This ranges anywhere from the complete absence of symptoms, to mental retardation, muscle weakness, liver problems, and unusual facial features.

Globoid Cell Leukodistrophy (GLD), also called Krabbe disease and galactosylceramide lipidosis, is an extremely rare inherited inborn error of metabolism (IEM). It is a degenerative disorder that affects the nervous system. It has an estimated prevalence of 1/100,000 in the Northern European population and a worldwide incidence of 1/100,000-1/250,000 live births. GLD is an autosomal recessive disorder that is caused by a deficiency of an enzyme called galactosylceramidase. Galactosylceramidase is a lysosomal protein that hydrolyzes the galactose ester bonds of ceramides and ceramide derivatives including galactocerebroside, galactosylsphingosine (psychosine), lactosylceramide, and monogalactosyldiglyceride. More specifically, galactosylceramidase is an enzyme that is involved in the catabolism (via the removal of galactose) of galactosylceramide, a major lipid in myelin, kidney, and epithelial cells of the small intestine and colon. Defects in galactosylceramidase lead to the accumulation of cytotoxic psychosine, which ultimately leads to apoptosis of oligodendrocytes and demyelination. As a result, this enzyme deficiency impairs the growth and maintenance of myelin, the protective sheath around nerve cell axons that ensures that electrical impulses are rapidly transmitted. GLD is part of a group of disorders known as leukodystrophies, which result from the loss of myelin (demyelination). GLD is also characterized by the abnormal presence of globoid cells, which are globe-shaped cells that often have multiple nuclei. There are three different phenotypes for GLD: infantile, juvenile, and late-onset. Neurodegeneration and early death (at age 2-3) occur in most infantile cases. In juvenile patients, the disease is often fatal 2-7 years after the symptoms begin. Adult-onset patients can survive many years after symptoms first manifest. The symptoms of infantile GLD usually begin during the first year of life. Typically, the initial signs and symptoms include feeding difficulties, episodes of fever without any sign of infection, irritability, stiff posture, muscle weakness, and slowed mental and physical development. Muscles continue to weaken as the disease progresses which decreases the infant's ability to move, chew, swallow, and breathe. It is also common for affected infants to experience vision loss and seizures. Treatment is limited to hematopoietic stem cell transplantation in pre-symptomatic infantile patients and mildly affected late-onset patients. Stem cell transplants have been shown to slow the progression of the disease.

Leukotriene C4 synthetase deficiency is caused by a defect in the enzyme leukotriene C4 synthetase (LTC4S). This enzyme catalyzes the synthesis of leukotriene C4 (LTC4) through conjugation of LTA4 with reduced glutathione (GSH), which is synthesized by glutathione synthetase. Leukotriene C4 and its receptor-binding metabolites LTD4 and LTE4 are cysteinyl leukotrienes that are potent lipid mediators of tissue inflammation. In general, leukotrienes are potent proinflammatory mediators synthesized from membrane-derived arachidonic acid after activation of certain granulocytes. A defect in LTC4 results in decreased concentrations of cysteinyl leukotrienes LTC4, LTD4 and LTE4 in plasma, spinal fluid and urine. Symptoms include early death, failure to thrive, motor retardation, microcephaly, and progressive neurological defect.

Succinic Semialdehyde Dehydrogenase (SSADH) deficiency is a rare autosomal recessive inherited disorder affecting the metabolism of γ-aminobutyric acid (GABA). With reduced GABA activity, oxidation of succinic semialdehyde (SSA) to succinic acid is impaired causing a build up of SSA and ultimately it’s downstream metabolite γ-hydroxybutyric acid (GHB). Symptoms of SSADH deficiency are primarily neuropsychiatric including developmental delays, hypotonia, expressive language impairment, seizures, difficulty coordinating movements (ataxia), decreased reflexes (hyporeflexia), and other behavioral issues. Patients with SSADH deficiency have elevated levels of GHB in urine, however this method is not a definitive diagnosis due to the potential volatilization of acidified urine and the use of GHB as a drug. Instead SSADH can be confirmed suing enzyme analysis in leukocytes and molecular genetic analysis of the Aldh5a1 gene at chromosome 6p22.

Canavan Disease (Canavan-Van Bogaert-Bertrand Disease; Aminoacylase 2 Deficiency; Spongy Degeneration of the Central Nervous System; Aspartoacylase Deficiency; ASP Deficiency; ACY2 Deficiency; ASPA) is a rare autosomal recessive disease caused by a defect in the ASPA gene which codes for aspartoacylase. A deficiency in this enzyme results in accumulation of N-Acetyl-L-aspartic acid in plasma, spinal fluid, and urine. Symptoms, which present at birth, include myclonus, irritability, hypotonia, motor retardation, and poor head control. The neurological complications are due to demyelination of neurons and leukodystrophy. Premature death often results, though lithium citrate can be used as a treatment.

Phosphoenolpyruvate Carboxykinase Deficiency 1 (PEPCK1), also called Phosphoenolpyruvate carboxykinase-1 (PCK1) deficiency, Phosphopyruvate carboxylase deficiency, Phosphoenolpyruvate carboxylase deficiency, Phosphoenolpyruvate carboxykinase deficiency, or PEP carboxykinase deficiency, is a rare inborn error of metabolism (IEM) and an autosomal recessive disorder of gluconeogenesis caused by a deficient PEPCK1 enzyme. PEPCK1 catalyzes the conversion of amino acids into sugars, mainly glucose, which is important in preventing hypoglycemia. This disorder is characterized by a large accumulation of lactic acid in the blood. Symptoms of the disorder include hepatomegaly, failure to thrive and liver failure, depending on the severity of the case. Treatment including heavy carbohydrates and fasting is very effective. It is estimated that Phosphoenolpyruvate Carboxykinase Deficiency 1 has only affected 10 individuals around the world according to medical literature.

Glycogenosis, Type IC, a sub-category of glycogen storage disease type I, is a rare inborn error of metabolism (IEM) and caused by a defective glucose-6-phosphatase translocase. Glucose-6-phosphate translocase transports glucose 6-phosphate from endoplasmic reticulum (ER) to cell, which glucose 6-phosphate is required for various pathways as the substrate. This disorder damages the ability of converting glycogen into glucose. Symptoms of the disorder include longer sleeping time through night, tiredness and seizures due to low blood sugar. Treatment with diet management is very effective. Currently, only few cases have been reported.

Tyrosinemia type I, also known as fumarylacetoacetase or FAH deficiency, is the most severe type of tyrosinemia, a buildup of tyrosine in the body. It is caused by an autosomal recessive mutation in the the FAH gene that encodes for fumarylacetoacetase, an enzyme that is responsible for the last of five steps that are involved in the metabolic breakdown of tyrosine in the liver and kidneys. The lack of this enzyme's function leads to a buildup of 4-fumarylacetoacetic acid as it couldn't be broken down to fumaric acid and acetoacetic acid. This also leads to an increased concentration of maleylacetoacetic acid. This eventually leads to the increased concentration of L-tyrosine in the body. Symptoms of tyrosinemia type I include jaundice and an enlarged liver, kidney dysfunction, as well as a failure to grow, as foods with high protein and amino acids lead to increased symptoms. Additionally, individuals are more at risk for future liver cancer.

Tyrosinemia II also known as Richner-Hanhart syndrome is an autosomal recessive disorder caused by a mutation in the TAT gene the encodes for tyrosine aminotransferase. A defect in this enzyme causes excess tyrosine to accumulate in the blood and urine, tyrosine crystals to form in the cornea, and increased excretion in the urine of 4-hydroxyphenylpyruvic acid, hydroxyphenyllactic acid, and p-hydroxyphenylacetic acid. Symptoms commonly appear in early childhood and include: mental retardation, photophobia (increased sensitivity to light), excessive tearing, eye redness and pain and skin lesions of the palms and soles. The patient is treated with restriction of dietary phenylalanine and tyrosine. Sometimes a tyrosine degradation inhibitor is also used to prevents the formation of fumarylacetoacetate from tyrosine. Trosinemia II is commonly misdiagnosed as herpes simplex keratitis.

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.