What enzyme is defective in McArdles disease and what is the clinical presentation?
Glycogen storage disease: defect in myphosphorylase (an isoenzyme of glycogen phosphorylase) that converts muscle glycogen to glucose 1 phosphate (which is converted to glucose-6-phos and used by the muscle for energy)
Muscle cramps with exercise
What is are the primary signs and symptoms in patients with fructokinase deficiency?
This disease is asymptomatic, however large amounts of fructose will be found in the urine
How to patients with fructokinase deficiency process fructose?
Hexokinase in the liver catalyzes the conversion of fructose to fructose-6-phosphate. This pathway is not usually used in normal people.
F6P can then be used in the glycolytic pathway or converted to glucose-6-phosphate by phosphoglucoisomerase.
Name the enzyme that is defective in Maple Syrup Urine Disease. What is the result of this enzyme deficiency?
Caused by a defect in alpha-keto acid dehydrogenase
This leads the the defective breakdown of leuine, isoleucine, and valine (the branched chain amino acids)
The increase in alpha-keto acids leads to neuro toxicity
What is ornithine transcarbamylase deficiency? How is it inherited?
Most common inherited urea cycle disorder is a deficiency of ornithine transcarbamylase (X-linked recessive unlike the other urea cycle enzyme deficiencies which are autosomal recessive)
List a few signs and symptoms of ornithine transcarbamylase deficiency:
- often evident in the first few days of life (but may appear later) - ↑ orotic acid in blood and urine (excess carbomyl phosphate converted to orotic acid, a pyrimidine synthesis intermediate) - ↓ BUN (no urea produced due to enzyme deficiency) - symptoms of hyperammonemia (should be distinguished from orotic aciduria which has ↑ orotic acid with no hyperammonemia)