Name short: MCD

Name long: Multiple carboxylase deficiency

Description: (There are 2 MCDS; this one chosen by phenotype description in Therrell.) Biotinidase deficiency is a late-onset form of multiple carboxylase deficiency, an inborn error of biotin metabolism that, if untreated, is characterized by seizures, breathing difficulties, hypotonia, skin rash, alopecia, hearing loss and delayed development. BTD deficiency is caused by mutations in the BTD gene (biotinidase) resulting in reduced or absent BTD activity. This enzyme catalyzes the hydrolysis of biocytin, a normal product of biotin-dependent carboxylase degradation, to biotin and lysine. The process results in the regeneration of free biotin. Biotin is an essential water-soluble vitamin and is the coenzyme for 4 carboxylases necessary for normal metabolism in humans.

Incidence in the US 2001-2010: 12 in 23.1 million screens (0.5 cases per million).

Implicated genes:
Biotinidase, BTD


Variants in BTD (see gnomAD page):
total variable positions: 421
rare variants: 0
common variants: 0
Allele frequency of rare (<0.001) variants and the implied number of homozygotes and compound heterozygotes, per million births (under the naive assumption that gnomAD captures all variants present in the human population; PSC = premature stop codon):

Population All rare variants Rare, resulting in PSC Rare, not intronic and not silent Known disease related All presumably detrimental
all 0 => 0 0 => 0 0 => 0 0 => 0 0 => 0
afr 0 => 0 0 => 0 0 => 0 0 => 0 0 => 0
amr 0 => 0 0 => 0 0 => 0 0 => 0 0 => 0
asj 0 => 0 0 => 0 0 => 0 0 => 0 0 => 0
eas 0 => 0 0 => 0 0 => 0 0 => 0 0 => 0
fin 0 => 0 0 => 0 0 => 0 0 => 0 0 => 0
nfe 0 => 0 0 => 0 0 => 0 0 => 0 0 => 0
oth 0 => 0 0 => 0 0 => 0 0 => 0 0 => 0
sas 0 => 0 0 => 0 0 => 0 0 => 0 0 => 0


Expected number of homozygotes/compound heterozygotes in a demographic profile close to the US, using all known (as in, listed in gnomAD) rare nontrivial variants as causative variants: 0.

Expected number of homozygotes/compound heterozygotes in a demographic profile close to the US, using all presumably harmful variants as causative variants: 0.

Enzyme structure. Representative chain shown as white cartoon, with positions of known mutations shown as red sticks. Blue: physiological ions. Pink: substrates and cofactors.



Total estimated number of casses per million (all presumably harmful variants): 0.

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