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Questions and Answers
What is the end product of body metabolism?
What is the end product of body metabolism?
Urine
What is the name of the metabolic disorder that affects tyrosine breakdown and causes a failure to inherit the gene for producing phenylalanine hydroxylase enzyme?
What is the name of the metabolic disorder that affects tyrosine breakdown and causes a failure to inherit the gene for producing phenylalanine hydroxylase enzyme?
Phenylketonuria (PKU)
PKU can be detected as early as 4 hrs after birth.
PKU can be detected as early as 4 hrs after birth.
True
What is the most well-known blood test for PKU?
What is the most well-known blood test for PKU?
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What is the name of the procedure developed by Robert Guthrie for PKU screening?
What is the name of the procedure developed by Robert Guthrie for PKU screening?
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What is the color of the urine in alkaptonuria?
What is the color of the urine in alkaptonuria?
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Albinism is associated with deficient melanin production.
Albinism is associated with deficient melanin production.
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What is the name of the disorder that affects the breakdown of branched-chain amino acids, leading to a maple syrup odor in urine?
What is the name of the disorder that affects the breakdown of branched-chain amino acids, leading to a maple syrup odor in urine?
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What is the name of the genetic disorder linked to a deficiency of isovaleryl coenzyme A in the leucine pathway, and often characterized by a distinctive "sweaty feet" odor?
What is the name of the genetic disorder linked to a deficiency of isovaleryl coenzyme A in the leucine pathway, and often characterized by a distinctive "sweaty feet" odor?
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Hartnup disease is associated with "blue diaper syndrome".
Hartnup disease is associated with "blue diaper syndrome".
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In cystinuria, which specific amino acid builds up in urine due to an inability for the renal tubules to reabsorb it?
In cystinuria, which specific amino acid builds up in urine due to an inability for the renal tubules to reabsorb it?
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Cystinosis is an inherited metabolic disorder.
Cystinosis is an inherited metabolic disorder.
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What is the name of the compound that is elevated in urine in porphyria, leading to a characteristic red or port wine color?
What is the name of the compound that is elevated in urine in porphyria, leading to a characteristic red or port wine color?
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What is the name of the disorder that is associated with a deficiency of the enzyme hypoxanthine guanine phosphoribosyltransferase and results in the accumulation of uric acid in the body?
What is the name of the disorder that is associated with a deficiency of the enzyme hypoxanthine guanine phosphoribosyltransferase and results in the accumulation of uric acid in the body?
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Which of the following tests can be used to detect reducing sugars in urine?
Which of the following tests can be used to detect reducing sugars in urine?
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What is the name of the disorder associated with an inability to metabolize galactose to glucose and can result in infant failure to thrive, liver disorders, cataracts, and severe mental retardation?
What is the name of the disorder associated with an inability to metabolize galactose to glucose and can result in infant failure to thrive, liver disorders, cataracts, and severe mental retardation?
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What is the name of the screening test for lactose in pediatric patients?
What is the name of the screening test for lactose in pediatric patients?
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What is the color of the precipitate produced in a positive fructose screening test?
What is the color of the precipitate produced in a positive fructose screening test?
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Study Notes
Urine Screening for Metabolic Disorders
- Urine is the end product of metabolism, reflecting protein and carbohydrate metabolism, errors in metabolism, and toxic substances.
- Abnormal constituents or conditions in urine can indicate inherited or metabolic disorders.
- Routine urinalysis can detect these abnormal constituents.
Inherited Metabolic Disorders
- Phenylketonuria (PKU): Inability to produce phenylalanine hydroxylase enzyme. Detected early (within 4 hours of birth). Lowers phenylalanine levels from 4mg/dL to 2mg/dL. Can cause mental retardation. Diagnosed through newborn screening and dietary restrictions. Blood test using Bacillus subtilis is a common method.
- Tyrosinemia: Accumulation of tyrosine due to enzyme deficiencies. Various types exist (Type 1, 1a, 1b, 2, 3).
- Alkaptonuria: Inability to produce homogentisic acid oxidase. Darkened urine after standing (brown or black), and deposition of brown pigment in joints (arthritis possible).
Other Metabolic Disorders
- Organic acidemias: Accumulation of organic acids in the blood and urine.
- MSUD (Maple Syrup Urine Disease): Accumulation of branched-chain amino acids (leucine, isoleucine, valine) in the blood and urine. Strong maple syrup odor in urine. Can result in mental retardation or death. Early detection and dietary restriction crucial for good prognosis.
- Cystinuria: Inability of renal tubules to reabsorb cystine, leading to elevated levels in urine and formation of kidney stones.
- Cystinosis: Incomplete metabolism of cystine leads to its deposition in various tissues. Can lead to renal failure.
- Homocystinuria: Defect in metabolism resulting in elevated levels of homocystine in blood and urine. Associated with cataracts, mental retardation, and thromboembolism.
Diagnostic Tests
- Guthrie Procedure: Measures phenylalanine levels in newborns.
- Ferric chloride test: Detects phenylpyruvic acid (positive result is a blue-green coloration).
- Nitroso-Naphthol Test: Tyrosine test and detection of tyrosine metabolites (positive result is orange-red color).
- Chromatography: Used for more advanced identification of various metabolites.
Additional Disorders
- Porphyrias: Defects in porphyrin metabolism leading to symptoms including photosensitivity and neurologic issues, and specific urine/feces/bile fluorescence tests.
- Melanuria (Melanism): Elevated urine melanin leading to darkened urine.
- Mucopolysaccharidoses: Accumulation of mucopolysaccharides (inorganic).
Other important points
- Color, odor, crystals, and other characteristics of urine can help in diagnosing specific metabolic diseases
- Early diagnosis is important for managing the associated diseases
- Dietary restrictions and other therapies are necessary for some inherited metabolic disorders.
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