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Inherited Metabolic Disorders of Carbohydrate Metabolism

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Inherited Metabolic Disorders of Carbohydrate Metabolism Dr. Essam H. Jiffri Glycogen Storage Diseases (Glycogenoses) -Glycogen storage diseases are a group of ... – PowerPoint PPT presentation

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Title: Inherited Metabolic Disorders of Carbohydrate Metabolism


1
Inherited Metabolic Disorders of Carbohydrate
Metabolism
  • Dr. Essam H. Jiffri

2
Glycogen Storage Diseases (Glycogenoses)
  • -Glycogen storage diseases are a group of
    inherited conditions characterized by
  • tissue deposits of glycogen that are abnormal
    in amount or structure.
  • -Glycogen is found principally in liver and
    muscle, and is synthesized from glucose
  • by different enzymes from those which mediate
    glycogenolysis.

3
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4
Features of Glycogen Storage Diseases
5
Features of Glycogen Storage Diseases
  • -Type I glycogenosis (von Gierke's disease) is
    caused by a deficiency in glucose-6-phosphatase,
    which results in impaired glucose release from,
    glycogen and thus hypoglycaemia.

6
Features of Glycogen Storage Diseases
  • -Lactate metabolism is also impaired as it is
    converted to glucose via glucose-6-phosphate in
    the Cori cycle, metabolic acidosis is a clinical
    feature.

7
Features of Glycogen Storage Diseases
  • -Hyperuricaemia is also seen, partly due to
    increased metabolism of glucose-6-phosphate via
    the pentose phosphate pathway, forming
    ribose-5-phosphate and purines (the catabolism
    of purines occurs through a common pathway
    leading to uric acid formation).

8
Features of Glycogen Storage Diseases
  • -In glycogen synthase deficiency, which is
    extremely rare, very little glucose is converted
    to glycogen, although conversion to lactate does
    occur, with
  • hyperglycaemia and hyperlactataemia being
    features of this deficiency.

9
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10
Disorders of Galactose Metabolism
  • Galactosaemia
  • -Impaired metabolism of galactose may result from
    three enzyme defects.
  • -The most common is galactose-l-phosphate uridyl
    transferase deficiency in which feeding
    difficulties, vomiting and hypoglycaemia occur
    soon after birth.

11
Disorders of Fructose Metabolism
  • Hereditary Fructose Intolerance
  • -Hereditary fructose intolerance is due to a
    deficiency of fructose-1-phosphate aldolase B
    which converts fructose into two 3-carbon units,
    mainly in the liver.

12
Disorders of Fructose Metabolism
  • Hereditary Fructose Intolerance
  • -Symptoms do not develop until sucrose is
    introduced into the diet, when hypoglycaemia and
    vomiting occur, probably as a result of
    intracellular
  • accumulation of fructose-l-phosphate.

13
Case Histories
  • Case 1
  • A 26-year-old patient expecting her second child
    was found to have glycosuria on routine testing
    of her urine in the antenatal clinic. An oral
    glucose tolerance test was carried out with the
    following results
  • Fasting blood glucose 4.9 mmol/L
  • (normal, 3.6-6.0 mmol/L)
  • 1-h blood glucose 6.4 mmol/L
  • 2-h blood glucose 5.2 mmolL
  • 1) Why was the OGTT performed ?
  • 2) What do the results indicate ?
  • 3) What is the most likely abnormality ?

14
  • Case 2
  • A 27-year-old patient with IDDM was admitted in a
    drowsy and confused state. The breath smelled of
    acetone and a history of a chest infection was
    obtained from a
  • relative. Initial investigations showed
    the following
  • Sodium 137 mrnol/L (normal, 137-144 mmol/L)
  • Potassium 5.7 mmol/L (normal, 3.3-4.4
    mmol/L)
  • Total Co2 11 mmol/L (normal, 24-31 mmol/L)
  • Urea 11.4 mmol/L (normal, 3.1- 7.9 mmol/l)
  • Blood glucose 23 mmol/L (normal, 3.6-6.0
    mmol/L)
  • 1) What is the explanation for the low total Co2
    result ?
  • 2) Why were the plasma potassium and urea levels
    increased ?
  • 3) What is the most likely abnormality?
  • 4) What other analyte may be measured to confirm
    diagnosis ?
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