Indications for Testing

There are three general types of circumstance in which fragile X testing should be considered: 1) a clinical presentation suggestive of fragile X syndrome, 2) a family history of fragile X syndrome or intellectual disabilities of unknown cause, or 3) risk of inheritance of fragile X syndrome by a fetus. Since the clinical presentation of fragile X syndrome is so varied, mental retardation, developmental delay, learning disabilities or autism are sufficient in males or females to warrant testing. Presence of one or more of the physical or behavioral features often associated with fragile X syndrome increases suspicion of the syndrome but is not necessary for testing to be appropriate.

Specific indications for testing:

• Any male or female with mental retardation (borderline to severe), developmental delay or learning disabilities of unknown cause.
• Any male or female with autism or autistic-like characteristics.
• Any male or female with a relative who has fragile X syndrome or mental retardation of unknown cause.
• Anyone with a previous positive or equivocal result by the fragile X cytogenetic test. Confirmation of the presence of the FMR1 mutation is important.

In the obstetric setting:

• Women or their spouses with a family history of fragile X syndrome or mental retardation of unknown cause.
• Women with a family history of premature menopause.
• Fetus of a pregnant woman known to be a fragile X carrier.

Guidelines to aid clinicians in making referrals for fragile X syndrome testing are also included in a policy statement on fragile X syndrome diagnostic and carrier testing produced by the American College of Medical Genetics (1994).

In the search for a cause of mental retardation or developmental delay in an individual, it is important that routine chromosome analysis (cytogenetic testing) be ordered in addition to fragile X testing or as a follow-up if results of fragile X DNA testing are negative. Routine chromosome analysis checks the appearance of all chromosomes and can pick up abnormalities other than fragile X syndrome that could cause intellectual impairment.

Annette K. Taylor, M.S., Ph.D.
Kimball Genetics, Inc.
101 University Boulevard, Suite 330
Denver, CO 80206
800-320-1807

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This page last updated Tuesday, June 24, 2008