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Metabolic Diseases

7 out of 9

Deficiency of enzyme keto acid decarboxylase leading to a block in the metabolism of branch chain amino acids is observed in - (AIIMS May 2013)

A Maple syrup urine disease
B Hartnup's disease

C Alkaptonuria
D Phenylketonuria

Ans. A

Maple Syrup urine disease

a. It is an inherited (autosomal recessive) disorder of branched chain amino acid i.e. - Valine, Leucine and lsoleucine.

b. Maple syrup urine disease (MSUD) is d/t defect in enzyme - a-keto acid dehydrogenase.

c. It is a mitochondrial, enzyme complex consisting of a a-ketoacid decarboxyluse a Dihydrolipoyl dehydrogenase and a Transacylase

d. The early steps in the metabolism of these three amino-acids are similar. One of the steps - decarboxylation is accomplished by a complex enzyme system i.e. branched chain a-keto acid dehydrogenase using thiamine pyrophosphate (vitamin B,) as a coenzyme. Deficiency of this enzyme system causes the disease, named after the sweet odour of maple syrup found in the body fluids - urine, sweat etc.

e. Clinical features

Affected infants are initially normal at birth but develop poor feeding and vomitting during the l" week of life lethargy and coma may ensue within a few days.

f. Physical examination reveals hypertonicity and muscular rigidity, with opisthotonos (spasm in which the body forms a bow like figure) Periods of hypertonicity may alternate with bouts of flaccidity.

Convulsion occur in most infants, and hypoglycemia is common (However in contrast to most hypoglycemic states, correction o/'the blood glucose level does not improve the clinical condition).

Metabolic Diseases Flashcard List

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