Urine Screening Fo Metabolic Disorders

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Metabolic disorders

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Renal type:
-caused by malfunction in tubular reabsorption
Overflow type:
-caused by disruption of a normal metabolic pathway:
-result is increased plasma concentrations of nonmetabolized substances

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Metabolic disorders

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Most metabolic disorders occur from protein, fat, CHO metabolism
-disruption of enzyme function
-lack of enzyme production: lack gene, this is known as an inborn error of metabolism (IEM)
-disease which causes organ malfunction
-toxic reactions
Now we do newborn screenings for IEM: heel stick

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Amino Acid Disorders:

Phenylalanine-Tyrosine Disorders

Phenylketonuria (PKU)

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-an aminoaciduria, 1/10,000-20,000 births
-can lead to mental retardation
-gives mousy odor to urine

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Phenylketonuria (PKU)

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-urine contains increased amounts of ketoacids such as phenylpyruvate
-failure to inherit gene that produces enzyme phenylalanine hydroxylase
-restrict diet, alternate pathways for phenylalanine metabolism will develop
-first test, Guthrie- a microbial inhibition assay

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Phenylketonuria (PKU)

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-cutoff is 2 mg/dl
-urine as follow up testing, monitoring diet in at risk pregnant women
-screening: ferric chloride reaction tube test for phenylpyruvic acid

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Tyrosyluria

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-tyrosinemia results is tyrosine in urine
-includes tyrosine and its degradation products
-causes can be metabolic or inherited
-can result in liver and tubular disease
-3 types

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Tyrosyluria

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-Type 1: generalized tubular disorder and progressive liver failure soon after birth
-Type 2: corneal erosion, lesions on palms, fingers, soles of feet
-Type 3: mental retardation of diet is not restricted
-screening: nitroso-naphthol tube test

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Melanuria

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-results from disruption in the second metabolic pathway of tyrosine
-affects production of melanin, thyroxine, epinephrine and others: albinism from lack of pigment melanin
-urine turns dark when exposed to air
-overproduction of melanocytes causes melanomas which secrete a precursor of melanin
-tests: ferric chloride, Na nitroprusside, Ehrlich’s

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Alkaptonuria

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urine turns dark from becoming alkaline from standing at room temp
-lacks enzyme homogentisic acid oxidase
-no completion of pathway: homogentisic acid accumulates in blood, tissues and urine
-brown stained or red colored diapers
-brown stains deposit in tissues- liver and cardiac disorders

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Alkaptonuria

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-tests: *ferric chloride, Clinitest, add alkali to freshly voided urine, silver nitrate and NH4OH, spectrophotometric
-distinguish between melanin and homogentisic acid

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Branched-Chain Amino Acids Disorders

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Contain a methyl group that braches from the main aliphatic
-accumulation of one or more early degradation products
-accumulation of organic acids further down the metabolic pathway: organic acidemias

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Maple Syrup Urine Disease (MSUD)

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a rare IEM, involving leucine, isoleucine, valine
-beginning of pathway is normal- ketoacids produced
-lack enzyme for decarboxylation of ketoacids- build up in blood and urine
-infants have failure to thrive and maple syrup odor to urine: early detection to prevent mental retardation and death
-restrict diet, monitor urinary ketoacids

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Maple Syrup Urine Disease (MSUD)

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included in newborn screening tests
-test: 2,4-dinitrophenylhydrazine (DNPH) reaction- adding to positive urine makes yellow precipitate
-on multistix/ chemstrips?

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Organic Acidemias

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-includes isovaleric, propionic, methylmalonic acidemia
-cause severe illness: vomiting, hypoglycemia, ketonuria, elevated serum ammonia levels
-Isovaleric acidemia: urine and patients have sweat feet odor: lack enzyme isovaleryl coenzyme A in the leucine pathway
-need MS/MS methodology for newborn screen
-no other tests

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Tryptophan Disorders

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characterized by increased urinary excretion of 5-hydroxyindolacetic acid (5-HIAA) and indican

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Indicanuria
Tryptophan Disorders

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-caused by intestinal obstruction
-tryptophan converted to indole

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5-HIAA
Tryptophan Disorders

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-a degradation product of serotonin
-accumulations of 5-HIAA are caused by tumors
-use random or first morning specimens
-consider diet before testing

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Cystine Disorders
Cystinuria

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-a defect in renal transport of amino acids
-tubules can’t reabsorb cystine filtered by the glomerulus
-can involve cystine, lysine, ornithine, arginine
-form renal calculi at young age
-in UA: crystals
-test: sodium nitroprusside

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Cystinosis

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-an IEM causing a sulfur odor to urine
-nephropathic: membrane defects prevent release of cystine into cytoplasm for metabolism: causes cystine deposits in the body (cornea, bone marrow, lymph nodes, organs)—can progress to renal failure
-nonnephropathic: benign- some ocular involvement

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Homocystinuria

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-defective metabolism of methionine causes accumulation oh homocystine in the body
-failure to thrive, mental retardation, thomboembolic disorders, cataracts, death
-early screen, confirm with silver-nitroprusside

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Porphyrin Disorders
Porphyrins

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Intermediate compounds in heme production
Disorders are called porphyrias
3 primary porphyrins and 2 precursors
-precursors ά-aminolevulinic acid (ALA) and porphobilinogen
Blockage of heme synthesis can occur at several points: accumulation of product formed just before the interruption

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Porphyrins

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Can check urine, blood, stool, bile
Porphyrias can be inherited or acquired
-lead poisoning, iron deficiency, exposure to toxins, chronic renal or liver disease
-lack of gene for enzyme production are inherited
-urine may have a red or port wine color when exposed to air, stained teeth and diapers
-tests: Ehrlich’s and fluorescence

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Mucopolysaccharide Disorders

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Mucopolysaccharides
AKA glycosaminoglycans
Large compounds located in connective tissue
Defective metabolism of polysaccharide potion of the molecule causes accumulation in lysosomes of connective tissue
3 substrates can accumulate- need to identify specific enzyme

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Mucopolysaccharide Disorders

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Mucopolysaccharide con’t
Diseases
-Hurler’s Disease: accumulation in corneas
-Hunter’s Disease: rare in females
-for both: abnormal skeletal structure and mental retardation
-Sanfilippo Syndrome: mental retardation
-tests: turbidity and metachromatic spot staining

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Purine Disorders
Lesch-Nyhan Disease

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-lack of enzyme causes accumulation of uric acid throughout the body
-causes gout, renal calculi, motor defects, mental retardation
-in UA: uric acid

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Carbohydrate Disorders
Melituria

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Increased in urinary sugar, inherited
Clinitest positive for reducing substances, while chemstrip glucose oxidase is negative
Clinitest detects reducing substances: copper reduction test
Melituria includes galactosuria, lactosuria, fructosuria

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Carbohydrate Disorders
Galactosuria

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-inability to metabolize galactose to glucose: accumulation of galactose and toxic intermediates in the blood
-cause by deficiency of 1 or 3 enzymes
-GALT (galactose-1-phosphate uridyl transferase) deficiency leads to severe mental retardation and liver disorders
-part of newborn screening