3-methylcrotonyl-CoA carboxylase (3-MCC) deficiency

Alternative name 3-Methylcrotonylglycinuria
About the condition 3-MCC deficiency is an organic acid disorder. It is a hereditary disease that is caused by a missing enzyme needed to convert protein into energy.
Inheritance Autosomal recessive
Year screening started in WA 2005
Incidence in Australia Currently unknown
Enzyme defect
  • Deficiency of the enzyme 3-methylcrotonyl-CoA carboxylase
  • May be seen as part of multiple carboxylase deficiency
Symptoms if untreated
  • Hypoglycaemia
  • Episodic metabolic acidosis
  • Significant clinical heterogeneity
Metabolites on bloodspot screening Increased hydroxyisovalerylcarnitine (C5OH).
Diagnostic tests
  • Plasma acylcarnitine profile
  • Urine organic acids
  • MCCC1 and MCCC2 gene analysis
Treatment
  • Low-protein diet
  • Carnitine supplementation
  • IV glucose and bicarbonate during crisis episodes
Screening issues
  • Some children may be asymptomatic
  • Maternal 3-MCC deficiency may be detected incidentally