Name short: CIT

Name long: Citrullinemia

Description: Severe vomiting spells beginning at the age of 9 months and mental retardation were features of the first reported case, offspring of first-cousin parents; McMurray et al. (1962) found citrulline in very high concentration in serum, spinal fluid, and urine. (The amino acid citrulline gets its name from its high concentration in the watermelon Citrullus vulgaris.) Visakorpi (1962) also described a case of citrullinuria. Ammonia intoxication is another manifestation. The enzyme defect concerns argininosuccinic acid synthetase (EC 6.3.4.5). Tedesco and Mellman (1967) found that the enzyme has an altered Michaelis constant. Most cases of citrullinemia have pursued a severe course with symptoms from birth and death in the neonatal period in more than half of cases. Orotic aciduria is present as well as hyperammonemia.

Incidence in the US 2001-2010: 128 in 24.9 million screens (5 cases per million).

Implicated genes:
Argininosuccinate synthetase 1, ASS1


Variants in ASS1 (see gnomAD page):
total variable positions: 507
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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