Citrullinemia Type 1: ASS1 Sequencing

ASS1 sequencing is a molecular test used to identify variants in the gene associated with Citrullinemia, Type 1.

Turnaround Time

2 weeks

CPT Code(s)

81406

Cost

$1,500

Genes

• Citrullinemia Type 1

Citrullinemia type I is an inborn error of amino acid metabolism caused by the deficiency of argininiosuccinate synthase (ASS1), which performs the third enzymatic step in the urea cycle, condensing citrulline and aspartic acid to form argininosuccinic acid. Patients are often identified by newborn screening, due to an accumulation of citrulline in the blood. Citrullinemia type I exhibits a broad clinical spectrum. Most patients present with a severe neonatal form characterized by hyperammonemia, vomiting, lethargy, failure to thrive, seizures, spasticity and increased intracranial pressure. Patients typically progress quickly to a coma and the disorder is fatal unless treated promptly. Other patients may exhibit a milder later-onset form of the disorder, and others appear to be asymptomatic.

Molecular testing is useful to confirm the diagnosis and to identify the disease causing mutations within a family to allow for carrier testing and prenatal diagnosis.

Sanger Sequencing

The preferred sample type is 3-5 ml of peripheral blood collected in an EDTA (purple top) tube. Extracted DNA, dried blood spots, and saliva are also accepted for this test. Saliva samples must be submitted in an approved saliva kit. Contact the lab to receive a saliva kit or to have one sent to your patient.

The specimen should be kept at room temperature and delivered via overnight shipping. If shipment is delayed by one or two days, the specimen should be refrigerated and shipped at room temperature. Do not freeze the specimen. Samples collected on Friday can be safely designated for Monday delivery.

Prenatal diagnosis is available if the familial mutations are known. Additional fees for cell culture and maternal cell contamination may apply. Maternal cell contamination studies are required for all prenatal molecular tests. Contact the laboratory prior to sending a prenatal specimen.