Podcast
Questions and Answers
What is a consequence of acute tyrosinemia due to the absence of the enzyme FAH?
What is a consequence of acute tyrosinemia due to the absence of the enzyme FAH?
Which symptom is NOT commonly associated with chronic tyrosinemia in children?
Which symptom is NOT commonly associated with chronic tyrosinemia in children?
What is a major phenotypic manifestation of homocystinuria?
What is a major phenotypic manifestation of homocystinuria?
Which condition is characterized by a maple syrup odor and leads to severe illness shortly after birth?
Which condition is characterized by a maple syrup odor and leads to severe illness shortly after birth?
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Which diagnostic technique is used to identify phenylketonuria?
Which diagnostic technique is used to identify phenylketonuria?
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What is a common characteristic of inborn errors of metabolism (IEM)?
What is a common characteristic of inborn errors of metabolism (IEM)?
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Which of the following diseases is characterized by a musty or mousy odor in urine?
Which of the following diseases is characterized by a musty or mousy odor in urine?
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Which disorder is associated with a defect in the enzyme homogentisate 1,2-dioxygenase?
Which disorder is associated with a defect in the enzyme homogentisate 1,2-dioxygenase?
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Which of the following symptoms indicates glutaric acidemia type II?
Which of the following symptoms indicates glutaric acidemia type II?
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What is the likely consequence of untreated Phenylketonuria (PKU)?
What is the likely consequence of untreated Phenylketonuria (PKU)?
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Which amino acid disorder causes urine to have a rotten fish odor?
Which amino acid disorder causes urine to have a rotten fish odor?
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In the context of IEM, what is primarily affected by a defect in enzyme activity?
In the context of IEM, what is primarily affected by a defect in enzyme activity?
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What clinical feature is an indication of ornithine transcarbamylase deficiency?
What clinical feature is an indication of ornithine transcarbamylase deficiency?
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Study Notes
Inborn Errors of Metabolism (IEM) - Amino Acid Disorders
- IEMs are usually autosomal recessive genetic disorders.
- Diagnosis confirmed by biochemical assays of metabolites, DNA studies, and neuro-radiology.
- These disorders affect amino acid metabolism, impacting synthesis and degradation.
- IEMs arise from enzyme or transport protein defects, hindering metabolic pathways and leading to substrate buildup.
Specific Amino Acid Transport Disorders
- Cystinuria: Amino acid transport disorder.
- Dicarboxylic aminoaciduria: Amino acid transport disorder.
- Hartnup disease: Amino acid transport disorder.
Specific Amino Acid Storage Disorders
- Glutaric acidemia type II: Amino acid storage disorder.
Characteristic Symptoms and Diagnoses
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Urine odor: Provides clues to specific disorders—
- Maple syrup urine disease: Maple syrup odor.
- Glutaric acidemia: Sweaty feet odor.
- Phenylketonuria (PKU): Mousy or musty odor.
- Trimethylaminuria: Rotten fish odor.
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Specific IEMs and their characteristics:
- Phenylketonuria (PKU): Silent until untreated; leads to brain damage and developmental issues. Elevated phenylalanine levels (30-50 times normal) result in phenylalanine metabolites.
- Ornithine transcarbamylase (OTC) deficiency: Type 2 is life-threatening in infancy. Acute metabolic crisis marked by vomiting, respiratory issues, lethargy, and possible coma.
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Tyrosinemia: Hereditary; severe liver disease in infancy (autosomal recessive). Lack of fumarylacetoacetate hydrolase (FAH) enzyme causes a buildup of toxic metabolites; progressive liver and kidney damage results from this build up.
- Acute tyrosinemia: Poor weight gain, enlarged liver, swelling, bleeding tendency are seen in infants, frequently lethal before nine months without intervention.
- Chronic tyrosinemia: Enlarges liver/spleen, fluid build-up, poor weight gain, frequent vomiting/diarrhea. Eventually leads to cirrhosis; liver transplant needed.
- Homocystinuria: Phenotypic expression includes ectopia lentis, vascular disease, malar flush, osteoporosis, accumulation of homocysteine/methionine. Defective cystathionine synthase activity is the cause.
- Maple syrup urine disease: Severe illness in infants, lethargy progressing to coma, seizures, developmental delay, maple syrup odor. Branched-chain aminoacidemia and aminoaciduria.
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Alkaptonuria: "Black urine disease"; defect in homogentisate 1,2-dioxygenase enzyme. Homogentisic acid (alkapton) accumulates, causing cartilage damage (ochronosis/osteoarthritis), heart valve issues, and kidney stones.
Diagnostic Techniques
- Ferric chloride test: Used in diagnosis (for general).
- Ninhydrin paper chromatography: Used for diagnosis.
- Guthrie bacterial inhibition assay: Used in the diagnosis of PKU.
- Quantitative measurements of amino acids in plasma and urine: Used.
- GC for urine organic acid analysis: Used for diagnosis.
- Paper/TLC, plasma and urine: Can be used for diagnosis
- Plasma levels: 6.6 mg/ml
- Urine levels: 3.12 mmol/mmol of creatinine
Albinism
- Tyrosinase deficiency causes hair and skin pigment loss;
- Individuals with PKU may have light skin/hair at birth because of low tyrosine levels.
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Description
Test your knowledge on Inborn Errors of Metabolism (IEM) and the various amino acid disorders. This quiz covers specific transport and storage disorders, characteristics, and symptoms associated with these metabolic disorders. Challenge yourself and deepen your understanding of these genetic conditions.
