Urine Screening For Metabolic Disorders PDF

URINE SCREENING FOR METABOLIC DISORDERS TRYPTOPHAN DISORDERS LAWRENCE R. SANTIAGO, RMT  Tryptophan Disorders Courtesy of Reynan P. Borja, RMT Cystine Disorders Cystinuria  elevated amounts of amino acid cystine in the urine  dueto the inability of the renal tubules to rea...

URINE SCREENING FOR METABOLIC DISORDERS TRYPTOPHAN DISORDERS LAWRENCE R. SANTIAGO, RMT  Tryptophan Disorders Courtesy of Reynan P. Borja, RMT Cystine Disorders Cystinuria  elevated amounts of amino acid cystine in the urine  dueto the inability of the renal tubules to reabsorb cystine filtered by the glomerulus Homocystinuria  defects in the metabolism of the amino acid methionine produce an increase in homocysteine throughout the body.  elevated levels of homocysteine can result in cataracts, intellectual disability, thromboembolic problems, stroke, and death.  screening performed using MS/MS testing  early detection and a change in diet alleviates metabolic problems  cyanide nitroprusside test followed by silver nitroprusside test is used PORPHYRIN DISORDERS  Porphyrins are the intermediate compounds in the production of heme  three primary porphyrins (uroporphyrin, coproporphyrin, and protoporphyrin) and the porphyrin precursors (alpha-aminolevulinic acid [ALA] and porphobilinogen  synthesis of heme can be blocked at a number of stages.  Blockage of a pathway reaction results in the accumulation of the product formed just before the interruption.  Then detection and identification of this product in the urine, bile, feces, or blood can aid in determining the cause of a specific disorder  Most soluble porphyrins (readily appear in urine): ALA, porphobilinogen, uroporphyrin  Caproporphyrin is less soluble but is found in urine  Protoporphyrin is found in bile  Disorders of porphyrin metabolism are collectively termed porphyrias. They can be inherited or acquired from erythrocytic and hepatic malfunctions or exposure to toxic agents  Common causes of acquired porphyrias include: Lead poisoning Excessive alcohol intake Iron deficiency Chronic liver disease Renal disease  Inherited porphyrias are much rarer than acquired porphyrias. They are caused by failure to inherit the gene that producesan enzyme needed in the metabolic pathway.  An indication of the possible presence of porphyrinuria is the observation of a red or port wine color to the urine after exposure to air.  The port wine urine color is more prevalent in the erythropoietic porphyrias, and staining of the teeth also may occur.  presence of congenital porphyria is suspected sometimes from a red discoloration of an infant’s diapers. Screening for porphyrinuria  Ehrlich reaction and fluorescence under ultraviolet light in the 550- to 600-nm range  The Ehrlich reaction can be used only for the detection of ALA and porphobilinogen. Acetyl acetone must be added to the specimen to convert the ALA to porphobilinogen before performing the Ehrlich test. PURINE DISORDERS Lesch-Nyhan disease  inherited as sex-linked recessive results in massive excretion of urinary uric acid crystals  Failure to inherit the gene to produce the enzyme hypoxanthine guanine phosphoribosyltransferase is responsible for the accumulation of uric acid throughout the body.  Patients suffer from severe motordefects, intellectual disability, a tendency toward self-destruction, gout, and renal calculi.  Usually development is normal for the first 6 to 8 months, and often the first sign is uric acid crystals resembling orange sand in diapers. CARBOHYDRATE DISORDERS Galactosuria  inability to properly metabolize galactose to glucose.  The resulting galactosemia with toxic intermediate metabolic products results in infant failure to thrive combined with liver disorders, cataracts, and severe intellectual disability. Early detection of galactosuria followed by removal of lactose (a disaccharide containing galactose and glucose) from the diet can prevent these symptoms.  caused by deficiency of the following enzymes galactose-1-phosphate uridyl transferase (GALT), galactokinase (GALK), and UDP-galactose-4-epimerase (GALE)  GALT deficiency that causes the severe, possibly fatal, symptoms associated with galactosemia.  The enzyme (GALK) is measured in the red blood cells as part of the protocol of the newborn heel puncture.  people with deficiencies in the other two enzymes still may produce galactosuria but have negative newborn screening tests.