Holocarboxylase synthetase deficiency is an inherited metabolic disorder in which the body is unable to use the vitamin biotin effectively.

Mutations in the HLCS gene reduce the activity of holocarboxylase synthetase, preventing cells from using biotin effectively and disrupting many cellular functions.

[citation needed] This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered.

[citation needed] The signs and symptoms of holocarboxylase synthetase deficiency typically appear within the first few months of life, but the age of onset varies.

Affected infants often have immunodeficiency diseases, difficulty feeding, breathing problems, a skin rash, hair loss (alopecia), and a lack of energy (lethargy).