Browsing Pathways

Phenylketonuria, also called Folling disease, is a rare inborn error of metabolism (IEM) and autosomal recessive disorder that affects the proper processing of phenylalanine caused by a defective phenylalanine hydroxylase. Phenylalanine hydroxylase breaks down phenylalanine from the diet. This disorder is characterized by a large accumulation of phenylalanine in the blood and other tissues. Symptoms of the disorder include behavioural problems, psychiatric disorders and seizures. Treatment eating a diet limiting the intake of phenylalanine is very effective. It is estimated that phenylketonuria affects 1 in 15,000 individuals in the United States.

Prolidase deficiency is an autosomal recessive disorder. The enzyme prolidase cleaves iminodipeptides with N-terminal proline or hydroxyproline. Collagen has high levels of iminoacids therefore, these dipeptidases are important for collagen metabolism. A defect in this enzyme causes accumulation of imidodipeptides in urine. Symptoms include skin lesions, anemia, dysmorphism, mental retardation, and ptosis (drooping eyelid).

Ornithine transcarbamylase deficiency (OTC deficiency), is a rare inborn error of metabolism (IEM) and X-linked disorder of the urea cycle caused by a deficiency of ornithine transcarbamylase. Ornithine transcarbamylase is responsible for processing nitrogen produced by the urea cycle. This disorder is characterized by a large accumulation of ammonia in the bloodstream. Symptoms of the disorder include lethargy, seizures, or coma. Treatment with hemodialysis is very effective in patients with high ammonia blood levels. It is estimated that ornithine transcarbamylase deficiency affects 1 in 14,000 to 1 in 77,000 individuals. These estimates are very different because adults with the late-onset form of ornithine transcarbamylase deficiency are less likely to come to medical attention.

Type I primary hyperoxaluria (Glycolicaciduria) is caused by mutation in the gene encoding alanine-glyoxylate aminotransferase (AGXT). AGXT normally catalyzes the reaction from L-serine and pyruvate to 3-hydroxypyruvate and L-alanine and the reaction from L-alanine and glyoxylate to pyruvate and glycine. A defect in AGXT results in accumulation of glycolic acid, glyoxylic acid, and oxalate in urine. Symptoms include hematuria, myocarditis, nephrocalcinosis, peripheral neuropathy, and renal failure.

Porphyria variegata (PV) is a rare inborn error of metabolism (IEM) which arises from a defective gene called PPOX. PPOX is responsible for protoporphyrinogen oxidase. A defect in this enzyme results in the build up of several compounds, including porphobilinogen, 5-aminolevulinic acid, and in feces and urine, porphyrin and coproporphyrin. Of the wide range of symptoms which present themselves in affected individuals, some include abdominal pain, vomiting, and diarrhea. As well as seizures, hallucinations and skin sensitivity to light. Indeed, the skin sensitivity can be so extreme that skin pigmentation changes, scarring and blistering and even hair growth can ensue on exposed areas.

Tay-Sachs Disease (TSD; GM2-Gangliosidosis, type I; B-Variant GM2-Gangliosidosis; Hexosaminidase A Deficiency; HEXA Deficiency; Tay-Sachs Disease Variant B1), is an autosomal recessive lysosomal storage disease. TSD is caused by a mutation in the alpha subunit of the hexosaminidase A gene (HEXA), which codes for the enzyme hexosaminidase A. HEXA degrades GM2 gangliosides and other molecules with terminal N-acetyl hexosamines in the brain and other tissues. A defect in this enzyme causes accumulation of oligosaccharides in urine. The most lethal variant of this disease is the classical infantile Tay-Sachs disease, in which children exhibit developmental retardation, dementia and blindness, finally ending in death by the second or third years. Tay-Sachs disease also has debilitating juvenile and adult forms. The majority of cases of TSD are found among (but not limited to) the Ashkenazi Jews and French Canadians in Eastern Quebec. Symptoms include ataxia, visual impairment and loss, cherry-red spot on retinal macula, dystosis multiplex, mental retardation, myoclonus, encephalopathy and psychosis.

Hartunup Disorder (HND, Hartnup Disease) is an autosomal recessive disease caused by a mutation in the SLC6A19 which codes for sodium-dependent neutral amino acid transporter B(0). A deficiency in this enzyme results in accumulation of L-alanine, L-asparagine, L-histidine, indoleacetic acid, L-isoleucine, L-leucine, L-phenylalanine, L-serine, L-threonine, L-tryptophan, L-valine, and L-tyrosine in urine. Symptoms include pellagra, psychosis, ataxia, and mental retardation. Treatment includes nicotinamide.

Iminoglycinuria, also called familial iminoglycinuria, is an autosomal recessive disorder of renal reabsorption caused primarily by a defective SLC36A2 gene. SLC36A2 codes for a proton-coupled amino acid transporter which facilitates the reuptake of glycine, proline, and hydroxyproline. This disorder is characterized by a large accumulation of glycine, proline, and hydroxyproline in the urine. Symptoms of the disorder include urolithiasis and mental retardation.

Lysinuric protein intolerance (Hyperdibasic aminoaciduria II; Dibasic aminoaciduria II; Hyperdibasic aminoaciduria II; LPI), also called hyperdibasic aminoaciduria type 2 or familial protein intolerance, is an autosomal recessive metabolic disorder affecting amino acid transport. LPI is caused by a defect in SLC7A7, Solute carrier family 7, a cationic amino acid transporter. A defect in this enzyme results in accumulation of ammmonia and reticulocytes in blood; glutamine in plasma, carnitine and ferritin in serum, and arginine, lysine and ornithine in urine. Symptoms include bone marrow abnormality, growth retardation, hyperammoniemia, mental retardation, pancreatitis, and seizures.

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.