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3-Methylcrotonyl-CoA Carboxylase Deficiency (3-MCC Deficiency)

What is 3-MCC Deficiency?

3-MCC Deficiency is a genetic disorder that prevents the patient’s body from properly breaking down leucine, an amino acid. The buildup of leucine in the body can cause periods of “metabolic crisis“, in which patients experience poor appetite, lack of energy, irritability, weakness, nausea and/or vomiting. Untreated, these metabolic crises can bring about developmental delays and even more serious consequences such as coma and death. 3-MCC Deficiency usually presents itself within the first year of life. Babies born with 3-MCC Deficiency seem to be normal at birth, but may go on to develop symptoms later.

What are the symptoms of 3-MCC Deficiency?

Recently, some studies suggest that many of the children that have been screened and identified as having 3-MCC will never develop symptoms, but when symptoms of 3-MCC Deficiency occur, they may include:
  • Abnormality of leucine metabolism
  • Hypoglycemia (Low blood sugar)
  • Muscular hypotonia
  • Organic aciduria
  • Abnormality of movement
  • Failure to thrive in infancy (Faltering weight in infancy)
  • Hyperammonemia (High blood ammonia levels)
  • Abnormality of the cerebral vasculature
  • Respiratory insufficiency
  • Spasticity

What causes 3-MCC Deficiency?

According to 3MCC Deficiency Information for Health Professionals, produced by the Kansas Department of Health and Environment, 3MCC deficiency is an autosomal recessive disease, which means that it is inherited by parents that each carry one copy of the mutated gene, but do not show signs and symptoms of the condition. 3-MCC deficiency is caused by changes (mutations) in MCCC1 or MCCC2 gene.

How is 3-MCC Deficiency diagnosed?

New-born screening is helping to catch 3-MCC Deficiency in patients that might have gone undiagnosed before. Since many cases of 3-MCC Deficiency are asymptomatic, screening helps identify potential patients before symptoms occur or in spite of their absence. Outside of a screening, many of these very young patients are showing up with a poor appetite, extreme tiredness, irritability and other behavioral changes. Medical history, symptoms, physical exam, and lab tests are all used to diagnosis 3-MCC Deficiency. Baby’s First Test  is a website for families and healthcare providers. Providing information and resources about screening at the local, state, and national levels,  it serves as a centralized resource for newborn screening information.

What are the treatments for 3-MCC Deficiency?

Newborn screening identifies many new patients, but since many of these patients will not experience symptoms, treatment may not be necessary. Symptomatic patients will require an eating plan that is low protein and low in leucine. Patients with 3-MCC Deficiency should avoid fasting. Patients may see some relief of symptoms by using the supplement L-carnitine, according to 3MCC Deficiency Information for Health Professional.

Where can I find out more about 3-MCC Deficiency?

3-Methylcrotonyl-CoA Carboxylase Deficiency (3-MCC Deficiency) Articles