Browsing Pathways

Arginine:glycine amidinotransferase deficiency, also called AGAT deficiency, is an extremely rare inherited inborn error of metabolism (IEM) and an autosomal recessive disorder caused by a defective arginine:glycine amidinotransferase (AGAT) gene. It manifests as a creatine deficiency disorder. Only 14 individuals with AGAT deficiency have been reported. The AGAT enzyme catalyzes the transfer of an amidino group from arginine to glycine yielding ornithine and guanidinoacetate, which is the immediate precursor of creatine. Deficiencies in the AGAT enzyme, therefore, lead to low levels of ornithine, guanidinoacetate, and creatine. People with AGAT deficiency have mild to moderate intellectual disability and delayed speech development. Some affected individuals develop autistic behaviours that affect communication and social interaction. Individuals with AGAT deficiency may experience seizures, especially when they have a fever. Children with AGAT deficiency may not gain weight and grow at the expected rate (failure to thrive) and have delayed development of motor skills such as sitting and walking. Affected individuals may also have weak muscle tone and tend to tire easily due to their low creatine levels. The treatment for AGAT deficiency is creatine supplementation since the body cannot make the creatine on its own. Early-stage (fetal and early postnatal) creatine treatment has shown that those affected can develop normally and that early diagnosis and treatment can substantially improve the final prognosis of AGAT deficiency.

Arginine: Glycine Amidinotransferase Deficiency (AGAT Deficiency, Creatine Deficiency Syndrome, Creatine Deficiency due to AGAT Deficiency, GATM Deficiency) is caused by mutation in the GATM gene, which codes for L-arginine:glycine amidinotransferase, which catalyzes the reaction between L-arginine and glycine, transferring an amidino group from L-arginine to glycine, producing L-ornithine and guanidinoacetate, a precursor of creatine. A defect in this enzyme causes a decrease in concentration of creatine and guanidinoacetate in plasma and urine. Symptoms include mental and motor retardation, seizures, and delayed or abnormal speech development.

Very Long Chain Acyl CoA Dehydrogenase Deficiency (VLCADD) is a rare disorder that is inherited through an autosomal recessive trait, and prevents the body from properly metabolizing very long chain fatty acids. This disorder occurs in the mitochondria, where the metabolization of fatty acids takes place. Early-onset VLCADD patients usually begin to exhibit symptoms just days or weeks after birth. Hypoglycemia, lethargy and irritability are symptoms associated with this disorder. Patients will also be at risk for hypertrophic cardiomyopathy and other heart conditions from age two months to two years. It can be diagnosed through a research of family history and generally a urine analysis will reveal that the patient has reduced of absent ketone bodies. To help control acute episodes, treatment includes maintaining a high carbohydrate and low fat diet, and avoiding fasting for more than 12 hours.

Pyruvate Decarboxylase E1 Component Deficiency is caused by a defect in the PDHA1 gene which codes for mitochondrial pyruvate dehydrogenase E1 component subunit alpha, somatic form. This is a homotetrameric enzyme that catalyses the decarboxylation of pyruvic acid to acetaldehyde and carbon dioxide. A defect in this enzyme results in accumulation of lacate and pyruvate. Symptoms and signs include severe lactic acidosis in the newborns that usually leading to death, hypotonic, lethargic, seizures, mental retardation and spasticity.

Primary hyperolaria type 2 (PH2) is a rare condition resulting from glyoxylate reductase/hydroxypyruvate reductase (GR/HPR) enzyme deficiency. PH2 results in calcium oxalate (also known as oxalic acid) deposits and end-stage renal disease. These deposits may cause kidney damage or failure.

Aromatase deficiency is a rare inborn error of metabolism (IEM) and autosomal recessive disorder of mutations in the CYP19A1 gene. The CYP19A1 gene encodes for the enzyme aromatase. Aromatase converts androgens to estrogens which is vital for bone growth and regulation of blood sugar levels. Symptoms of decrease in estrogen and increase androgens such as testosterone can cause impaired female sexual development, unusual bone growth, insulin resistance, and a variety of other symptoms. It presents with virilization of pregnant mothers during the antenatal period, and virilization of female fetuses at birth. Treatments include lifelong hormone therapy. There have been about 20 reported cases of Aromatase Deficiency worldwide.

Fluvastatin inhibits cholesterol synthesis via the mevalonate pathway by inhibiting 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. HMG-CoA reductase is the enzyme responsible for the conversion of HMG-CoA to mevalonic acid, the rate-limiting step of cholesterol synthesis by this pathway. Fluvastatin bears a chemical resemblance to the reduced HMG-CoA reaction intermediate that is formed during catalysis. Fluvastatin was the first synthetically-prepared HMG-CoA reductase inhibitor. Although similar to lovastatin, simvastatin, and pravastatin, it has a shorter half-life, no active metabolites, extensive protein binding, and minimal CSF penetration. Cholesterol biosynthesis accounts for approximately 80% of cholesterol in the body; thus, inhibiting this process can significantly lower cholesterol levels.

CHILD Syndrome, (Congenital Hemidysplasia with Icthyosiform Erythroderma and Limb Defects; Ichthyosiform Eruthroderma, Unilateral, with Epsilateral Malformations, Especially Absence Deformity of Limbs) is caused by a mutation in the gene encoding NADH steroid dehydrogenase-like protein (NSDHL). A defect in sterol-4 alpha-carboxylate 3-dehydrogenase, which normally catalyzes the reaction 3-beta-hydroxy-4-beta-methyl-5-alpha-cholest-7-ene-4-alpha-carboxylate + NAD+ = 4-alpha-methyl-5-alpha-cholest-7-en-3-one + CO2 + NADH, causes accumulation of 8(9)cholestenol and 8-dehydrocholesterol in plasma. Symptoms of CHILD syndrome include hearing defects, hemidysplasia, unilateral hypomelia, ichthyosiform nevi, limb abnormalities, lung hypoplasia, and punctate calcifications.

Xanthinuria Type I is a condition caused by an autosomal recessive mutation. The condition was discovered (though not diagnosed) in 1817, when stones formed of almost pure xanthine were first identified by Marcet. The symptoms arise because of a malfunction in the production of xanthine oxidase. It is a rare . It is characterized by a loss of oxidase such as in serum and the uric acid found in peepee. As a result, the opposite is true for the presence of xanthine and hypoxanthine. They will be found in the latter and former in increased quantities. Although the condition can cause a wide range of symptoms including renal xanthine stones, what occurs most of the time is that xanthinuria is asymptomatic and diagnosis is product of chance.

Mercaptopurine is a purine antimetabolite prodrug that exerts cytotoxic effects via three mechanisms: via incorporation of thiodeoxyguanosine triphosphate into DNA and thioguanosine triphosphate into RNA, inhibition of de novo synthesis of purine nucleotides, and inhibition of Ras-related C3 botulinum toxin substrate 1, which induces apoptosis of activated T cells. Mercaptopurine travels through the bloodstream and is transported into cells via nucleoside transporters. Mercaptopurine is then converted to thioguanosince diphosphate through a series of metabolic reactions that produces the metabolic intermediates, thioinosine 5’-monophosphate, thioxanthine monophosphate, and thioguanosine monophosphate. Thioguanosine diphosphate is then converted via a thiodeoxyguanosine diphosphate intermediate to thiodeoxyguanosine triphosphate, which is incorporated into DNA. Thioguanosine diphosphate is also converted to thioguanosine triphosphate which is incorporated into RNA. The thioguanosine triphosphate metabolite also inhibits Ras-related C3 botulinum toxin substrate 1, a plasma membrane-associated small GTPase that regulates cellular processes, inducing apoptosis in activated T cells. Finally, de novo synthesis of purine nucleotides is inhibited by the methyl-thioinosine 5’-monophosphate metabolite, which inhibits amidophosphoribosyl-transferase, the enzyme that catalyzes one of the first steps in this pathway.