aetiology

Last reviewed 01/2018

Propionyl coenzyme A carboxylase (PCC) is involved in the catabolic pathway whereby specific amino acids (isoleucine, valine, methionine and threonione), odd chain fatty acids and gut derived propionic acid are converted into succincyl-CoA for incorporation into the Kreb's cycle.

At times of metabolic stress (such as in the first few days of life) proteolysis is increased.

Where PCC is deficient this leads to build up of the enzyme's substrate, propionic acid. The resulting metabolic acidosis triggers glycogenolysis and beta oxidation of fatty acids resulting in ketosis and a further worsening of the acidosis.

While propionic acidaemia is itself not a urea cycle defect, the increased levels of organic acids inhibit the urea cycle enzyme N -acetylglutamate synthase (NAGS). This inhibition results in hyperammonaemia.

Reference

• 1) British Inherited Metabolic Diseases Group: www.bimdg.org.uk
• 2) A Clinical Guide To Inherited Metabolic Diseases, Third Edition, JTR Clarke, Cambridge University Press
• 3) Clinical Chemistry, Fourth Edition, William J Marshall, Mosby
• http://emedicine.medscape.com/article/948084-overview