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Reviewed June 2006

What is the official name of the ASS1 gene?

The official name of this gene is “argininosuccinate synthase 1.”

ASS1 is the gene's official symbol. The ASS1 gene is also known by other names, listed below.

Read more about gene names and symbols on the About page.

What is the normal function of the ASS1 gene?

The ASS1 gene provides instructions for making an enzyme called argininosuccinate synthase 1. This enzyme participates in the urea cycle, which is a sequence of chemical reactions that takes place in liver cells. The urea cycle processes excess nitrogen that is generated as the body uses proteins. The excess nitrogen is used to make a compound called urea, which is excreted from the body in urine.

Argininosuccinate synthase 1 is responsible for the third step of the urea cycle. This step combines two protein building blocks (amino acids), citrulline and aspartate, to form a molecule called argininosuccinic acid. A series of additional chemical reactions uses argininosuccinic acid to form urea.

How are changes in the ASS1 gene related to health conditions?

citrullinemia - caused by mutations in the ASS1 gene

At least 50 mutations that cause type I citrullinemia have been identified in the ASS1 gene. Most of these mutations change single amino acids in the argininosuccinate synthase 1 enzyme. These genetic changes likely alter the structure of the enzyme, impairing its ability to bind to molecules such as citrulline and aspartate. A few mutations lead to the production of an abnormally short version of the enzyme that cannot effectively play its role in the urea cycle.

Defects in argininosuccinate synthase 1 disrupt the third step of the urea cycle, preventing the liver from processing excess nitrogen into urea. As a result, nitrogen (in the form of ammonia) and other byproducts of the urea cycle (such as citrulline) build up in the bloodstream. Ammonia is toxic, particularly to the nervous system. An accumulation of ammonia during the first few days of life leads to poor feeding, vomiting, seizures, and the other signs and symptoms of type I citrullinemia.

Where is the ASS1 gene located?

Cytogenetic Location: 9q34.1

Molecular Location on chromosome 9: base pairs 130,444,707 to 130,501,274

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBIThis link leads to a site outside Genetics Home Reference.)

The ASS1 gene is located on the long (q) arm of chromosome 9 at position 34.1.

The ASS1 gene is located on the long (q) arm of chromosome 9 at position 34.1.

More precisely, the ASS1 gene is located from base pair 130,444,707 to base pair 130,501,274 on chromosome 9.

See How do geneticists indicate the location of a gene? in the Handbook.

Where can I find additional information about ASS1?

You and your healthcare professional may find the following resources about ASS1 helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the ASS1 gene or gene products?

  • argininosuccinate synthetase 1
  • ASS
  • Citrulline-aspartate ligase
  • CTLN1

Where can I find general information about genes?

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

What glossary definitions help with understanding ASS1?

acids ; ammonia ; compound ; enzyme ; gene ; ligase ; molecule ; nervous system ; protein ; toxic ; urea

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

See also Understanding Medical Terminology.

References (6 links)


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

Reviewed: June 2006
Published: February 8, 2016