3-Methylcrotonyl-CoA Carboxylase Deficiency

What is 3-methylcrotonyl-CoA carboxylase deficiency?

3-methylcrotonyl-CoA carboxylase deficiency is an inherited disorder in which the body is unable to process certain proteins properly. People with this disorder have inadequate levels of an enzyme that helps break down proteins containing a particular building block (amino acid) called leucine.

Infants with this disorder appear normal at birth but usually develop signs and symptoms during the first year of life or in early childhood. The characteristic features of this condition, which can range from mild to life-threatening, include feeding difficulties, recurrent episodes of vomiting and diarrhoea, excessive tiredness (lethargy), and weak muscle tone (hypotonia). If untreated, this disorder can lead to delayed development, seizures, and coma. Early detection and lifelong management (following a low-protein diet and using appropriate supplements) may prevent many of these complications. In some cases, people with gene mutations that cause 3-methylcrotonyl-CoA carboxylase deficiency never experience any signs or symptoms of the disorder.

The characteristic features of this condition are similar to those of Reye syndrome, a severe disorder that develops in children while they appear to be recovering from viral infections such as chicken pox or flu. Most cases of Reye syndrome are associated with the use of aspirin during these viral infections.

How common is 3-methylcrotonyl-CoA carboxylase deficiency?

This condition affects an estimated 1 in 50,000 individuals worldwide.

What genes are related to 3-methylcrotonyl-CoA carboxylase deficiency?

Mutations in the MCCC1 and MCCC2 genes cause 3-methylcrotonyl-CoA carboxylase deficiency.

The MCCC1 and MCCC2 genes make protein subunits that come together to form an enzyme called 3-methylcrotonyl-CoA carboxylase. This enzyme plays an essential role in breaking down proteins from the diet. Specifically, the enzyme is responsible for the fourth step in processing leucine, an amino acid that is part of many proteins. If a mutation in the MCCC1 or MCCC2 gene reduces or eliminates the activity of 3-methylcrotonyl-CoA carboxylase, the body is unable to process leucine properly. As a result, toxic byproducts of leucine processing build up to harmful levels, damaging the brain and nervous system.

How do people inherit 3-methylcrotonyl-CoA carboxylase deficiency?

This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene but do not show signs and symptoms of the disorder.

What other names do people use for 3-methylcrotonyl-CoA carboxylase deficiency?

  • BMCC deficiency
  • Deficiency of methylcrotonoyl-CoA carboxylase
  • 3-MCC
  • MCC deficiency
  • Methylcrotonyl-CoA carboxylase deficiency
  • 3-methylcrotonylglycinuria

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