HLCS (Holocarboxylase Synthetase): HLCS is an enzyme vital for the proper function of carboxylase enzymes, which are crucial in the metabolism of proteins, carbohydrates, and lipids. Mutations in HLCS can lead to holocarboxylase synthetase deficiency, a rare metabolic disorder marked by multiple carboxylase deficiencies, resulting in problems with the skin, hair, immune system, and developmental delays.