Multiple carboxylase deficiency (MCD) is a rare metabolic disorder and an autosomal recessive disorder of biotin metabolism. Biotin is also known as Vitamin H and it is one of the Vitamin B complexes. Vitamin B helps our body to convert food into energy. Biotin is water-soluble and often contained a small amount of biotin in food such as eggs, milk, and banana.

Phenotype: (Ref: Malacards)

  • Hearing impairment
  • Muscular hypotonia
  • Cognitive impairment
  • Skin rash

There are two types of MCD:

(1) Biotinidase deficiency – Unable to re-utilize biotin. Caused by homozygous or compound heterozygous mutation in BTD gene chromosome 3p25.


Homozygous means that the particular gene or genes are having two same alleles.

Compound Heterozygous

A compound heterozygous (CH) means that each parent gives one alternate allele and the location of alleles are at different loci within the same gene. Two mutated alleles are required for the disease to be expressed.

(2) Holocarboxylase synthetase deficiency – by mutations in the HLCS gene (21q22.1).

Chromosome 21. Location 21q22.1

Phenotype of Holocarboxylase synthetase deficiency:

  • Unusual urine pH, variation from normal pH of 4.5 to 7.8.
  • Head or neck abnormality.
  • HLCS is associated with Organic acidemia ( metabolic disorder, unable to metabolize amino acid in the body).

This genetic disease does not prevalent in particular ethnicities. However, Biotinidase deficiency is high in Brazil (1:9000). (Ref: BTD).