Citrullinemia, Type 1 : ASS1 Sequencing

Test Information

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

Clinical Information

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.

Indications

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.

Methodology

Sanger Sequencing

Specimen Requirements

5 to 7 ml of peripheral blood collected in an EDTA (lavender top) tube is the preferred specimen type. The minimal blood needed for reliable DNA isolation is 3 ml. Extracted DNA, dried blood spots, and saliva are also accepted for this test.

Transport Instructions

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 Testing Information

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.

Have Questions Need Support?

Call our laboratory at 1-800-473-9411 or contact one of our Laboratory Genetic Counselors for assistance.
Robin Fletcher, MS, CGC
Kellie Walden, MS, CGC

Molecular Testing, Sanger Sequencing
Lucy's Story

Lucy's Story

When our daughter Lucy had a metabolic crisis at 7 days old, we were shocked and devastated to find out that she was born with a rare genetic disorder (MSUD). Her newborn screening results did not make it back in time to prevent the crisis, and no one at our local hospital was familiar with the disease. They did not know how to treat her. Calls were made to Greenwood Genetic Center to confirm her diagnosis...

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