Mendelian Inheritance in Man number: 300624

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Fragile X syndrome is one of the most common genetic causes of mental retardation in males with an estimated incidence of 1:4000-6250 in males.  Males affected with Fragile X typically have moderate mental retardation, and can present with characteristic physical features such as a long face, prominent ears and macroorchidism. Approximately 50% of females with full mutations are affected.  Their level of developmental impairment is, on average, less severe than that seen in males.  Fragile X is usually caused by a trinucleotide expansion in the FMR1 gene on the X chromosome.  Normal individuals have <40 CGG repeats. Individuals with pre-mutation alleles have 59-230 repeats whereas individuals with intermediate sized alleles (“gray zone” alleles) have 41-58 repeats, broadly defined.  Individuals with a full mutation have > 230- > 2000 repeats.


  • Family history of Fragile X
  • Patient with mental retardation, developmental delay, or autistic features


DNA is isolated and subjected to Eco RI and Eag I restriction digest followed by Southern blot analysis using the DNA probe, StB12.3 to determine methylation status of the FMR1 gene and approximate number of trinucleotide repeats.  Polymerase chain reaction analysis is used to further define the repeat number more precisely.



Minimum of 3 mL whole blood in EDTA (purple topped) tubes.


If the specimen is from clinics within UAB or Kirklin Clinic, please call 934-5562 for pickup. If specimens are being sent from some other location, please ship via UPS Overnight Priority.  Specimens must be packaged to prevent breakage and absorbent material must be included in the package to absorb liquids in the event that breakage occurs.  Also, the package must be shipped in double watertight containers (e.g. a specimen pouch + the shipping companies Diagnostic Envelope).  Please contact us (Email –, Phone – 205-934-5562) prior to sample shipment and provide us with the date of shipment and the tracking number of the package.

15 working days


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Test Requisition Form

Note: Detailed and accurate completion of this document is necessary for reporting purposes. The Medical Genomics Laboratory issues its clinical reports based on the demographic data provided by the referring institution on the lab requisition form. It is the responsibility of the referring institution to provide accurate information. If an amended report is necessary due to inaccurate or illegible documentation, additional reports will be drafted with charge.

Requests for Molecular Genetic testing will not be accepted for the following reasons:

  • No label (patients full name and date of collection) on the specimens
  • No referring physician’s or genetic counselor’s names and addresses
  • No billing information if being paid for by an institution
  • No informed consent

For more information, test requisition forms, or sample collection, please call: 205-934-5562.



Fu et al. Variation of the CGG repeat at the fragile X site results in genetic instability: resolution of the Sherman paradox. Cell. 1991 Dec 20;67(6):1047-58.

Hagerman RJ, Hagerman PJ. (2002) The fragile X premutation: into the phenotypic fold.  Curr Opin Genet Dev. 2002 Jun;12(3):278-83.

Hagerman PJ, Hagerman RJ. Fragile X-associated tremor/ataxia syndrome (FXTAS).  Ment Retard Dev Disabil Res Rev. 2004;10(1):25-30.

Nolin SL, et al. (2003) Expansion of the fragile X CGG repeat in females with premutation or intermediate alleles. Am J Hum Genet. 2003 Feb;72(2):454-64.

Oberle, et al.  Instability of a 550-bp DNA segment and abnormal methylation in Fragile X Syndrome.  Science 252:1097-1102 (1991).