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Disorders of Carbohydrate Metabolism- Quick Revision
|S.N.||Disease||Biochemical Defect and Pathogenesis||Inheritance and classification||Clinical manifestations||Lab.Investigations||Treatment|
|1.||Lactose Intolerance||Deficiency of lactase. Lactose present in ingested dairy products remains uncleaved and passes intact into the colon. The accumulated lactose produces osmotic effects and undergoes fermentation to produce a variety of abdominal manifestations.||There are three major types of lactose intolerance:1) Primary lactose intolerance- begins after about age 2
2) Secondary lactose intolerance occurs because of mucosal damage or from medications resulting from certain gastrointestinal diseases,
3) Congenital lactase deficiency present at birth, Autosomal recessive inheritance
|Common symptoms include – abdominal pain, bloating, gas, diarrhea, nausea.||1. Hydrogen Breath Test – Normally, very little hydrogen is detectable in the breath, but undigested lactose produces high levels of hydrogen. 2)Stool Acidity Test- Undigested lactose creates lactic acid and other fatty acids that can be detected in a stool sample.
Glucose may also be present in the stool as a result of undigested lactose.
|Lactose-free, lactose-reduced milk, Soy milk. Lactase enzyme drops or tablets
Getting enough calcium is important
|2.||Pyruvate kinase deficiency (PKD)||An erythrocyte enzymopathy involving Glycolysis. A discrepancy between erythrocyte energy requirements and ATP-generating capacity produces irreversible membrane injury, resulting in cellular distortion, rigidity, and dehydration. This leads to premature erythrocyte destruction by the spleen and liver with the resultant anemia.||Autosomal recessive||Severe anemia, jaundice, Kernicteruschronic leg ulcers,
Growth failure and failure to thrive
|Hb, Serum Bilirubin and confirmation by enzyme assays||Mild to moderate disease only supportive treatment. Severe case – blood transfusion or bone marrow transplantation can be done.
Splenectomy is indicated only in severe anemia.
|3.||PDH- complex deficiency||Pyruvate dehydrogenase complex (PDC) converts pyruvate to acetyl-coenzyme A (CoA), A deficiency in this enzymatic complex limits the production of citrate.
Because citrate is the first substrate in the citric acid cycle, the cycle cannot proceed.
Malfunction of this cycle deprives the body of energy.
An abnormal lactate buildup results in nonspecific symptoms.
|X-linked||Severe lethargy, poor feeding, tachypnea), especially during times of illness, stress, or high carbohydrate intake. Progressive neurological symptoms like developmental delay, intermittent ataxia, poor muscle tone, abnormal eye movements, or seizures are present in early infancy.
|Serum lactate and pyruvate levels,Urinary and serum Alanine level.
MRI for detection of neurological damage
|Symptomatic treatment. -Low carbohydrate diet Thiamine supplementation, –
Ketogenic diet and oral citrate to correct acidosis.
|4.||Glucose-6-phosphatase dehydrogenase (G6PD) deficiency||Glucose 6-phosphate dehydrogenase (G6PD) is an enzyme critical in the redox metabolism of all aerobic cells .In red cells, its role is even more critical because it is the only source of reduced nicotinamide adenine dinucleotide phosphate (NADPH), which, directly and via reduced glutathione (GSH), defends these cells against oxidative stress. With the help of the enzyme glutathione peroxidase, reduced glutathione converts harmful hydrogen peroxide to water. Deficiency leads to haemolytic anemia
|X-linked disorder||The vast majority of people remain asymptomatic throughout life other develop haemolytic anemia in response to oxidative challenges. Acute haemolytic anemia develops in response to ingestion of fava beans, drugs and infections.
Typically, a haemolytic attack starts with malaise, weakness, and abdominal or lumbar pain.
After an interval of several hours to 2–3 days, the patient develops jaundice and often dark urine, due to hemoglobinuria.
The onset can be extremely abrupt, especially with favism in children.
|Hb low-The anemia is moderate to extremely severe, usually normocytic and normochromic associated with hemoglobinuria,LDH is high and so is the unconjugated bilirubin,
The confirmation is done by measuring the actual enzyme activity.
|Identification and discontinuation of the precipitating agent Oxygen and bed rest, which may afford symptomatic relief.
Prevention of drug-induced hemolysis is possible in most cases by choosing alternative drugs.
|5.||Hereditary Galactosemia||Galactose-1-phosphate uridyl Transferase (GALT) deficiency is the most common enzyme deficiency that causes Galactosemia. The other enzyme deficiencies which can produce Galactosemia are- Galactokinase and Uridine diphosphate (UDP) galactose-4-epimerase enzyme deficiencies.||Autosomal recessive.||The cardinal features of classic galactosemia are hepatomegaly, cataracts, and mental retardation.Poor growth, liver dysfunction and jaundice are also present.||1. Urine test for reducing sugar is positive. The confirmation is done by thin layer chromatography.2.A galactose Tolerance Test is abnormal in these patients. There is much higher than normal rise in blood galactose after the administration of galactose, and the elevation persists for a much longer time than normal.
3.Serum Bilirubin and Transaminases may be high.
4-Confirmation is by enzyme estimation in erythrocytes.
|Galactose free diet is recommended to prevent the accumulation of galactose|
|6.||Hereditary fructose intolerance||Hereditary fructose intolerance is caused by mutation in the gene encoding Aldolase B enzyme. The rate of phosphorylation by fructokinase is very high and in the presence of Aldolase B deficiency
ATP depletion takes place which is manifested in the form of hyperuricemia, lacticacidemia and liver dysfunction.
|An autosomal recessive trait||These patients are healthy and asymptomatic until fructose or sucrose (table sugar) is ingested (usually from fruit, sweetened cereal, or sucrose-containing formula).Clinical features include recurrent abdominal pain, vomiting and hypoglycemia.
Long term exposure leads to liver and kidney failure.
|Urine test is positive for reducing sugar, aminoaciduria, proteinuria and phosphaturia may also be associatedLiver and kidney function tests may be abnormal.
The confirmation is done by enzyme estimation.
|Total avoidance of fructose containing foods.|
|7.||Essential Pentosuria||Deficiency of Xylitol dehydrogenase enzyme. This enzyme converts L Xylulose to Xylitol.
Failure to convert leads to accumulation of
L Xylulose in blood and is also excreted excessively in urine
|Autosomal recessive||Asymptomatic. Just a chance finding.||Urine test is positive for reducing sugar.Confirmation by Bial’s test and loading test by
|No treatment is needed|
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