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URINE SCREENING FOR METABOLIC DISORDERS

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Presentation on theme: "URINE SCREENING FOR METABOLIC DISORDERS"— Presentation transcript:

1 URINE SCREENING FOR METABOLIC DISORDERS
CHAPTER 8

2 Learning Objectives Upon completing this chapter, the reader will be able to Explain abnormal accumulation of metabolites in the urine in terms of overflow and renal disorders. Discuss the importance of and the MS/MS testing methods for newborn screening. Name the metabolic defect in phenylketonuria, and describe the clinical manifestations it produces. State three causes of tyrosyluria. Name the abnormal urinary substance present in alkaptonuria, and explain how its presence may be suspected. Discuss the appearance and significance of urine that contains melanin.

3 Learning Objectives (cont’d)
Describe a basic laboratory observation that has relevance in maple syrup urine disease. Discuss the significance of ketonuria in a newborn. Differentiate between the presence of urinary indican owing to intestinal disorders and Hartnup disease. State the significance of increased urinary 5-hydroxyindoleacetic acid. Differentiate between cystinuria and cystinosis, including the differences found during analysis of the urine and the disease processes.

4 Learning Objectives (cont’d)
Describe the components in the heme synthesis pathway, including the primary specimens used for their analysis, and explain the cause and clinical significance of major porphyrias and the appearance of porphyrins in urine. Define mucopolysaccharides, and name three syndromes in which they are involved. State the significance of increased uric acid crystals in newborns’ urine. Explain the reason for performing tests for urinary-reducing substances on all newborns.

5 Overflow Versus Renal Disorders
Disruption of a normal metabolic pathway Increased plasma concentrations of the nonmetabolized substances Overrides reabsorption ability of renal tubules Inherited lack of specific enzyme for protein, fat, or carbohydrate metabolism—inborn error of metabolism Renal Malfunctions in the tubular reabsorption mechanism

6 Disorders Classified by Defect
Overflow Inherited Metabolic Renal Phenylketonuria Infantile tyrosinemia Hartnup disease Tyrosinemia Melanuria Cystinuria Alkaptonuria Indicanuria Maple syrup urine disease 5-Hydroxyindoleacetic acid Organic acidemias Porphyria Cystinosis Mucopolysaccharidoses Galactosemia Lesch-Nyhan disease Table 8–2 Major Disorders of Protein and Carbohydrate Metabolism Associated with Abnormal Urinary Constituents, Classified by Functional Defect

7 Phenylalanine/Tyrosine Metabolic Pathway
Current state-mandated screening for as many as 30 or more inborn errors of metabolism (IEM) Urine tests are primarily for follow-up Disorders can cause abnormal urinalysis results Heel stick blood tests are used for testing Performed before infant leaves hospital But >24 h Metabolites appear first in the blood Analyze by tandem mass spectrophotometry, MS/MS

8 Phenylalanine/Tyrosine Metabolic Pathway

9 Amino Acid Disorders (Aminoacidurias)
Phenylketonuria, tyrosyluria, alkaptonuria Phenylketonuria 1 in 10,000 to 20,000 births Autosomal recessive; heterozygotes normal Eliminate phenylalanine from diet (milk) Damage to child’s mental capacity Alternate pathways as child matures Avoid ↑ phenylalanine foods (aspartame)

10 Amino Acid Disorders (Aminoacidurias)(cont'd)
Phenylalanine hydroxylase is missing Urine test Urine and 5% ferric chloride produces a permanent green-blue color

11 Tyrosyluria/Tyrosinemia
Metabolic defects Premature transient tyrosinemia Underdevelopment of liver function Acquired severe liver disease Hereditary defects Type 1: enzyme deficiency is fumarylacetoacetate acid hydrolase; renal tubular disease and liver failure in infants

12 Tyrosyluria/Tyrosinemia (cont’d)
Hereditary defects Type 2: enzyme deficiency is tyrosine aminotransferase; corneal erosion and lesions on hands and feet Type 3: enzyme deficiency is p-hydroxyphenylpyruvate oxidase; mental retardation if no dietary restrictions (milk) Screening tests Screening tests using MS/MS are available for tyrosinemia types 1, 2, and 3

13 Melanuria Second pathway for tyrosine Melanin
Melanin, thyroxine, epinephrine, protein, and tyrosine sulfate Melanin Pigment for dark hair, skin Defect causes albinism Increased production = malignant melanoma 5,6-dihydroxyindole Dark urine from oxidation of melanogen to melanin

14 Alkaptonuria Enzyme deficiency is caused by a failure to inherit the gene to produce the enzyme homogentisic acid oxidase Third major defect in the phenylalanine-tyrosine pathway Black alkaline urine, possible black-stained diapers Manifests later in life with brown pigment deposits in tissues Urine: blue with ferric chloride, yellow precipitate with Clinitest, black with silver nitrate and ammonium hydroxide; quantitative tests available

15 Branched Chain Amino Acid Disorders
Amino acids with a methyl group that branches from the main aliphatic carbon chain Two groups Maple syrup urine disease (MSUD); early degradation products accumulate Organic acidemias; accumulation of organic acids further down in pathway Ketonuria in a newborn

16 Maple Syrup Urine Disease (MSUD)
Inborn error of metabolism, autosomal recessive Amino acids involved are leucine, isoleucine, and valine 1-week failure to thrive is noticed Urine: strong odor of maple syrup, and thick, dark appearance Dietary regulation by day 11 shows good outcomes Positive urine ketones Screening test 2,4-dinitrophenylhydrazine produces yellow precipitate turbidity

17 2,4-Dinitrophenylhydrazine (DNPH) Test
Place 1 mL of urine in a tube. Add 10 drops of 0.2% 2,4-DNPH in 2N HCl. Wait 10 minutes. Observe for yellow or white precipitate.

18 Organic Acidemias Early: severe vomiting, metabolic acidosis, hypoglycemia, ketonuria Isovaleric, propionic, methylmalonic acidemias Isovaleric: “sweaty feet odor” from patient Deficiency of isovaleryl coenzyme A Propionic and methylmalonic: no conversion of valine, threonine, methylmalonate to succinyl coenzyme A Isovaleric, propionic, and methylmalonic acidemias can be detected by newborn screening programs using MS/MS

19 Tryptophan Disorders Increased urinary excretion of the metabolites indican and 5-hydroxyindoleacetic acid (5-HIAA)

20 Indicanuria Tryptophan enters intestine, is reabsorbed or is converted to indole by bacteria, and leaves in the feces Intestinal disorders and Hartnup disease cause increased tryptophan conversion to indole Increased indole reabsorbed, excreted by kidney on its way to the liver Exposure of urine to air = indigo blue

21 Indicanuria (cont’d) Hartnup disease: blue diaper syndrome
Inherited disorder affects intestinal reabsorption of indole and renal tubular reabsorption = Fanconi syndrome Requires dietary supplements: niacin

22 5-Hydroxyindoleacetic Acid (5-HIAA)
Tryptophan produces serotonin Serotonin from tryptophan is produced by the intestinal argentaffin cells and is carried in the body to the muscles by platelets Excess excreted in the urine as 5-HIAA Argentaffin (enterochromaffin) cell tumors = ↑ ↑ 5-HIAA in urine from excess serotonin produced

23 5-Hydroxyindoleacetic Acid (5-HIAA)(cont'd)
Urine test Nitrous acid and 1-nitroso-2-naphthol produce purple to black color Normal 2 to 8 mg/day, >25 mg/day in disease Can perform test on random specimens Patient instructions No bananas, pineapples, tomatoes, phenothiazines, and acetanilids for 72 hours 24-hour urine samples must be preserved with HCl or boric acid

24 Cystine Disorders Two different disorders; both have noticeable odor of sulfur Cystinuria Inherited disorder affecting renal reabsorption Two modes of inheritance: (1) only cystine and lysine are not reabsorbed; (2) cystine, lysine, arginine, and ornithine are not reabsorbed Increased calculi formation early in life for both modes Approximately 65% of the people in whom all four amino acids are affected can be expected to produce calculi early in life

25 Cystine Disorders (cont’d)
Cystine is the least soluble accounting for cystine crystals Cystine is also the only amino acid found during the analysis of calculi from these patients Urine screening test: cyanide-nitroprusside Na cyanide reduces cystine, and nitroprusside produces a red-purple color if excess cystine is present False-positives: ketonuria, homocystinuria

26 Cyanide-Nitroprusside Test
Place 3 mL of urine in a tube. Add 2 mL sodium cyanide. Wait 10 minutes. Add five drops 5% sodium nitroprusside. Observe for red-purple color.

27 Cystinosis Genuine IEM
Ranging from a severe fatal disorder developed in infancy to a benign form appearing in adulthood Two categories Nephropathic Infantile Later life Non-nephropathic Defect in lysosomal membranes prevents release of cystine into cytoplasm for metabolism = crystalline cystine deposits in body

28 Cystinosis (cont’d) Deposits: cornea, bone marrow, lymph nodes, organs
Renal tubules are affected by deposits causing Fanconi syndrome, which is not inherited Infantile: rapid progression to renal failure Late-onset: gradual progression to renal failure Non-nephropathic: benign, some ocular problems Laboratory: aminoaciduria, reducing substances, cystine crystals Renal transplants and cystine-depleting medications

29 Homocystinuria Defect in metabolism of methionine, producing increased methionine in body Failure to thrive, cataracts, mental retardation, thromboemboli, death Requires changes in diet Additional screening with silver nitrate instead of sodium cyanide Included in newborn screening programs performed using MS/MS testing

30 Silver Nitroprusside Test
Place 1 mL of urine in a tube. Add two drops concentrated NH4OH. Add 0.5 mL 5% silver nitrate. Wait 10 minutes. Add five drops sodium nitroprusside. Observe for red-purple color.

31 Heme Synthesis

32 Porphyrin Disorders Intermediate compounds in the production of heme
Primary porphyrins: uroporphyrin, coproporphyrin, protoporphyrin Precursors: α-aminolevulinic acid (ALA) and porphobilinogen Detection of pathway disruptions in urine, blood, bile, and feces Urine: ALA, porphobilinogen, urobilinogen Feces/bile: coproporphyrin, protoporphyrin Blood: free erythrocyte protoporphyrin (FEP) for lead poisoning

33 Porphyrin Disorders (cont’d)
Collectively termed porphyrias Inherited: gene in metabolic pathway is missing Classified by clinical symptoms as neurologic/psychiatric, cutaneous/photosensitivity, or both Acquired (more common): lead poisoning, alcoholism, iron deficiency, chronic liver and renal disease

34 Porphyrin Disorders (cont’d)
Urine: port wine color after air exposure, also seen on diapers Ehrlich reaction: only for ALA and porphobilinogen Convert ALA to porphobilinogen by adding acetyl acetone Watson-Schwartz test Ehrlich reaction now included on the Multistix urobilinogen pad Fluorescence under ultraviolet light 550- to 600-nm range is used for other porphyrins; extract into glacial acetic acid and ethyl acetate; does not distinguish Violet, pink, red, based on concentration

35 Mucopolysaccharide Disorders
Inherited disorders preventing the metabolism of glycoaminoglycans in the connective tissue Incompletely metabolized polysaccharides accumulate in connective tissue Substances found in urine are dermatan sulfate, keratan sulfate, and heparin sulfate

36 Mucopolysaccharide Disorders (cont’d)
Mucopolysaccharidoses Hurler syndrome: abnormal skeletal structure, severe mental retardation, and corneal damage Hunter syndrome: abnormal skeletal structure, severe mental retardation, inherited as a sex-linked recessive trait, rare in females Sanfilippo syndrome: mental retardation Bone marrow transplantation and gene therapy

37 Urinary Screening Tests
Acid-albumin and cetyltrimethylammonium bromide turbidity tests Thick, white precipitate Metachromatic staining procedures Positive urine produces a blue color that cannot be washed away with dilute acidified methanol

38 Cetytrimethylammonium Bromide (CTAB) Test
Place 5 mL of urine in a tube. Add 1 mL 5% CTAB in citrate buffer. Read turbidity in 5 minutes.

39 Mucopolysaccharide Paper Test
Dip filter paper into 0.59% azure A dye in 2% acetic acid. Dry. Add one drop of urine to paper. Wash with 1 mL acetic acid mL methanol diluted to a liter. Observe for blue color.

40 Purine Disorders Lesch-Nyhan disease Inherited sex-linked recessive
Massive excretion of uric acid crystals Motor defects, mental retardation, self-destruction, gout, renal calculi Normal development 6 to 8 months Orange sand in diaper Be alert for increased uric acid crystals in pediatric patients

41 Carbohydrate Disorders
Termed melituria; frequently due to inherited disorder No problems except for galactosuria Three enzymes: most important is galactose-1-phosphate uridyl transferase (GALT) also included in MS/MS screens Failure to thrive, severe mental retardation, cataracts, liver disorders Remove lactose from diet Included in newborn testing of RBCs Clinitest positive

42 Other Meliturias Lactosuria Fructosuria Pentosuria
Pregnancy and lactation Fructosuria Parenteral feeding Resorcinol screening test Pentosuria Ingestion of large amounts of fruit


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