Holocarboxylase Synthetase Deficiency (MCD)



Holocarboxylase synthetase deficiency (MCD) is a condition in which the body is unable to break down proteins and carbohydrates. People with this condition have trouble using biotin, a vitamin that helps turn certain carbohydrates and proteins into energy for the body. MCD can lead to a harmful buildup of organic acids and toxins in the body. Early detection and treatment often can prevent the severe outcomes of MCD. Signs of MCD begin in infancy, usually in the first few days of life, and include poor appetite, sleeping longer or more often, tiredness, irritability, muscle weakness (hypotonia), vomiting, peeling skin rash, and hair loss (alopecia). Many of these signs may occur when a baby eats foods the body cannot break down. Symptoms can be triggered by long periods of time without eating, illnesses, and infections. 

Condition Type:

Core Conditions


Holocarboxylase synthetase deficiency (MCD) is estimated to affect 1 out of every 87,000 people.

More Information for Parents:
Also known as:
  • Holocarboxylase synthetase deficiency
  • HCSD
  • Holocarboxylase deficiency
  • HLCS deficiency
  • Early-Onset multiple carboxylase deficiency
  • Multiple carboxylase deficiency
  • Neonatal form of MCD
  • Multiple Co-A carboxylase deficiency

Core Conditions