aldolase
Summary
Aldolase B is a liver enzyme that catalyzes the cleavage of fructose-1-phosphate in the fructose metabolism pathway; its deficiency causes hereditary fructose intolerance. Serum aldolase (muscle isoform) is also used as a nonspecific marker of muscle damage, similar to CK.
Detail
Aldolase exists as several tissue-specific isoenzymes (A in muscle, B in liver/kidney/intestine, C in brain). Aldolase B is critical in both fructolysis and gluconeogenesis, catalyzing conversion of fructose-1-phosphate to dihydroxyacetone phosphate (DHAP) and glyceraldehyde, and fructose-1,6-bisphosphate to DHAP and glyceraldehyde-3-phosphate in glycolysis/gluconeogenesis. Hereditary fructose intolerance (HFI) is an autosomal recessive disorder caused by aldolase B deficiency, leading to accumulation of fructose-1-phosphate after fructose ingestion. This depletes hepatic phosphate and inorganic phosphate stores, inhibiting glycogenolysis and gluconeogenesis, causing severe hypoglycemia, vomiting, jaundice, hepatomegaly, and failure to thrive in infants after introduction of fruits/juices/sucrose. Diagnosis involves genetic testing or enzyme assay; treatment is strict avoidance of fructose, sucrose, and sorbitol. This contrasts with essential fructosuria (benign, fructokinase deficiency). Separately, serum aldolase (mainly muscle isoform A) is elevated in conditions with muscle breakdown such as polymyositis, dermatomyositis, muscular dystrophy, and rhabdomyolysis, often paralleling elevated CK levels, and can be used as an ancillary marker when CK is normal or to monitor disease activity.
Sources
- First Aid for the USMLE Step 1
- Harper's Illustrated Biochemistry
- Robbins Basic Pathology
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