Other Causes Of Mellituria: Lactosuria, Fructosuria, Galactosemia And Pentosuria
Food Sources Of Lactose
Lactosuria And Fructosuria
Asides calcific pancreatitis being the cause of Mellituria (which is actually the major cause), there are other causes of this ailment. They are lactosuria, fructosuria, galactosemia and pentosuria.
Newborn babies ingesting milk may develop lactosuria. The urinary level of lactose increases with the quantity ingested. Lactosuria is common in women during pregnancy and lactation.
After the intake of large amounts of fructose- containing foods like berries, grapes and honey, even normal persons develop fructosuria, the alimentary fructosuria.
Rarely, fructosuria is due to deficiency of the specific enzyme, fructokinase in the liver. This is called essential fructosuria. This condition is benign since most of the ingested fructose can be utilized by other metabolic pathways.
Hereditary fructose intolerance is a more serious metabolic error caused by the deficiency of hepatic fructose-1-phosphate aldolase. This is transmitted as an autosomal recessive. These subjects develop postprandial hypoglycemia. The clinical picture varies with age. The severe form presents in infancy. The baby is normal when breast fed, but vomiting foods, or sucrose and sorbitol (which yield fructose on digestion) are introduced into the diet. The baby fails to thrive. Other accompaniments of the condition are hepatomegaly, jaundice, evidences of hepatic dysfunction, postprandial hypoglycemia, renal tubular acidosis, amino-acidurias and lactic acidosis. If left untreated, the condition proceeds to portal or biliary cirrhosis. If the abnormality is recognized early and fructose is avoided, all the lesions clear up. In older children and adults, the disease presents with nausea, abdominal pain, distension and diarrhea. Since sugar and sweets precipitate these attacjs; such persons learn to avoid these items. Hepatic involvement is less marked, but uricosuria and renal stones are more common.
Diagnosis: This should be suspected clinically from the history. Precipitation of hypoglycemia by small doses of fructose (0.25g/Kg body weight in adults or 3 g/m2 body surface in children) establishes the diagnosis. In normal subjects, hypoglycemia is induced only by large doses of fructose.
Hereditary fructosuria has to be distinguished from other metabolic disorders like galactosemia and tyrosinosis.
Food Sources Of Fructose
Galactosemia And Pentosuria
Normally, lactose present in milk is converted into glucose and galactose by intestinal lactase. Galactose is absorbed and converted to glucose in the liver. Conversion into glucose is defective in galactosemia and hence the concentration of galactose-1-phosphate and galactose increase in blood and tissues such as liver, brain, kidneys, intestines and lens.
Galactosemia is transmitted as an autosomal recessive. In the fully developed form, classical galactosemia presents with cataract, mental retardation, hepatic cirrhosis and death in early life. The enzyme galactose-1-phosphate uridyl transferase is deficient. The severe form manifests within a few days of birth with intolerance of milk, vomiting, refusal to feed, and failure to thrive. Soon, jaundice, hepatomegaly and hepatic dysfunction develop. Cataracts develop within weeks or months. As the child grows up, mental deficiency becomes evident. Recurrent bacterial infections (E.Coli) are common and may be fatal.
In the nonclassical form of galactosemia, the enzyme galactokinase is deficient. Galactokinase is required to convert galactose into galactose-1-phosphate and in its absence, galactose accumulates in blood and tissues. The only complication in this disorder is cataract formation.
Diagnosis: Urine shows galactose. Diagnosis is established by demonstrating the deficiency of galactose-1-phosphate uridyl transferase in erythrocytes. Treatment consists of dietary measures to avoid milk and milk products and this results in dramatic improvement. Even in advanced cases, dietary management leads to regression of symptoms except the cataract.
Pentosuria can be due to ingestion of excessive pentose found in grapes, cherries, plums etc. and this is known as alimentary pentosuria. The pentoses are arabinose, apiose, thamnose, ribose, and xylose. Essential pentosuria is an inherited disorder transmitted as an autosomal recessive trait and the urinary pentose is L-xylulose. It is caused by the deficiency of xylitol dehydrogenase. The condition is clinically silent and no treatment is required. The pentosuria is controlled by avoiding fruits.
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