Detection and sizing of CGG repeat expansions in the FMR-1 gene.
Performing Laboratory / Facility
UCLA Medical Center Clinical Laboratory (CHS)
Performing Section
Molecular Pathology
Availability
Monday through Friday, 0700-1700
Turnaround Time
14 days from receipt of specimen in performing lab
Methodology
Polymerase Chain Reaction (PCR) amplification with a fluorescent labeled primer and detection of product(s) by electrophoresis on an ABI 3130xl genetic analyzer. Southern Blot: Digestion with methylation sensitive and methylation insensitive enzymes, electrophoresis and detection with a chemiluminescent probe.
Use
To detect CGG repeat expansions in the FMR-1 gene.
Limitations
PCR test can detect CGG repeat lengths up to the full mutation range (about 200 repeats). The Southern Blot method detects both moderate and high premutations and full mutation CGG repeat expansions, but cannot accurately size them. Sizing is not required for full mutations, but it is useful for premutations the latter is accomplished by the PCR assay.
Additional Information
PCR: Detection and accurate sizing of FMR-1 premutations is useful for carrier screening and genetic counseling in individuals with a family history of mental retardation with features of fragile X syndrome. Detection of full FMR-1 repeat expansions for diagnostic purposes requires Southern blot analysis, and this method will be employed automatically on any case in which a full mutation allele cannot be visualized by PCR. Southern blot: This test is used primarily to diagnose or rule out fragile X syndrome in males or females with mental retardation, developmental delay, or other stigmata of fragile X syndrome. It is performed automatically on any case giving indeterminate results by the PCR method. Methylation analysis is useful to distinguish the two FMR-1 genes in females (since one of them lies on the inactive, methylated X-chromosome) and to determine the pathologic potential of a full mutation (since the fragile X phenotype is caused by both CGG repeat expansion and methylation of the cytosines in the repeat).
Detection and sizing of CGG repeat expansions in the FMR-1 gene.
Performing Laboratory / Facility
UCLA Medical Center Clinical Laboratory (CHS)
Performing Section
Molecular Pathology
Availability
Monday through Friday, 0700-1700
Turnaround Time
14 days from receipt of specimen in performing lab
Methodology
Polymerase Chain Reaction (PCR) amplification with a fluorescent labeled primer and detection of product(s) by electrophoresis on an ABI 3130xl genetic analyzer. Southern Blot: Digestion with methylation sensitive and methylation insensitive enzymes, electrophoresis and detection with a chemiluminescent probe.
Use
To detect CGG repeat expansions in the FMR-1 gene.
Limitations
PCR test can detect CGG repeat lengths up to the full mutation range (about 200 repeats). The Southern Blot method detects both moderate and high premutations and full mutation CGG repeat expansions, but cannot accurately size them. Sizing is not required for full mutations, but it is useful for premutations the latter is accomplished by the PCR assay.
Additional Information
PCR: Detection and accurate sizing of FMR-1 premutations is useful for carrier screening and genetic counseling in individuals with a family history of mental retardation with features of fragile X syndrome. Detection of full FMR-1 repeat expansions for diagnostic purposes requires Southern blot analysis, and this method will be employed automatically on any case in which a full mutation allele cannot be visualized by PCR. Southern blot: This test is used primarily to diagnose or rule out fragile X syndrome in males or females with mental retardation, developmental delay, or other stigmata of fragile X syndrome. It is performed automatically on any case giving indeterminate results by the PCR method. Methylation analysis is useful to distinguish the two FMR-1 genes in females (since one of them lies on the inactive, methylated X-chromosome) and to determine the pathologic potential of a full mutation (since the fragile X phenotype is caused by both CGG repeat expansion and methylation of the cytosines in the repeat).
