Diagnostic Test Directory

Molecular Genetics Laboratory

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Laboratory Update

Testing for the Noonan spectrum of disorders is now available at the Molecular Genetics Laboratory. Learn more about Noonan spectrum testing »

ARX-Related Disorders (ARX Known Mutation)

  • Synonyms: X-linked lissencephaly with abnormal genitalia (XLAG), West syndrome, ISSX1, EIEE1, Partington Syndrome, X-linked Mental Retardation, X-linked Infantile Spasms
  • LIS Mnemonic: MBARXKNWN


    Collect whole blood in a purple top (EDTA) tube.

    Volume Required

    3 ml whole blood or 1 ug

    Minimum Required

    3 ml whole blood


    Refrigerate sample until shipment. Send the sample at room temperature with overnight delivery for receipt Monday through Friday within 24 hours of collection.


    Whole blood can be refrigerated until shipment.

    Unacceptable conditions

    Heparinized specimens, severely hemolyzed specimens, frozen, clotted or possibly commingled specimens, blood in non-sterile or leaky containers, mislabeled or inappropriately labeled specimens.

    Specimen Handling

    Do not heat, freeze or centrifuge blood before shipment. Refrigerate sample until shipment.

Days Performed

Mon - Fri 9:00am to 4:00pm


2-3 weeks



Disease Information

Clinical Features:

Mutations in the ARX gene lead to different nonsyndromic as well as syndromic forms of mental retardation: Partington syndrome (PRTS), X-linked infantile spasms syndrome (ISSX), X-linked lissencephaly with abnormal genitalia (XLAG), X-linked myoclonic epilepsy with spasticity and intellectual disability (XMESID), and non syndromic X-linked mental retardation (MRX). More recently, ARX mutations have been identified in several women with isolated agenesis of the corpus callosum (Proud syndrome) and in men with hydranencephaly.

Molecular Genetics:

ARX is located on Xp22 and contains 5 coding exons. ARX belongs to the Aristaless-related Paired-class homeodomain protein family and acts as a transcription factor involved in the organization of primary axes in a developing embryo. Mutations identified in ARX have included polyalanine repeat tract expansions, missense mutations, nonsense mutations, premature termination mutations, frameshift mutations, splice site mutations, duplications/insertions, and large deletions.

Test Methods:

Sequence analysis of the mutation previously identified in a family member will be performed.

Detection Rate:

The analytical sensitivity of this assay is ~99%.

Related Tests:

Prenatal testing is available to adult females who are confirmed carriers of mutations. Please contact the laboratory director to discuss appropriate testing prior to collecting a prenatal specimen.


Test results with interpretation will be mailed and/or faxed to the referring physician or laboratory following completion of the test. Additional reports will be provided as requested.


The clinical utility of such testing is to support a clinical diagnosis of the disease, facilitate genetic counseling, assess the risk to other first degree relatives and to facilitate testing of at - risk family members.

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