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University of Iowa Diagnostic Laboratories (UIDL) Department of Pathology Room 5231, RCP Iowa City, Iowa 52242-1181 319-384-7212 Tel 319-384-7213 Fax |
FRAGILE X SYNDROME INFORMATION
| Background: |
Size and methylation status of the CGG triplet repeat region of the FMR-1 gene is determined by Southern blot and PCR analysis of genomic DNA. Alleles with up to 44 CGG repeats are considered normal, or stable, while alleles with between 45 and 54 repeats fall into an inconclusive range in which both stable and unstable alleles can occur. Premutation alleles normally have between 55 and 200 CGG repeats and, while not associated with fragile X syndrome, may exhibit expansion to full mutations when passed on to offspring. Alleles with over 200 repeats are considered full mutations and are associated with fragile X syndrome in most males. The genotype-phenotype correlation is not precise enough to be used clinically. In the absence of triplet repeat expansion, the standard cytogenetic analysis may prove useful to clarify the clinical diagnosis. For information on performing routine cytogenetics, call the Cytogenetics laboratory at (319)356-3877 or the Division of Medical Genetics at (319) 356-2674. |
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| Selected References: |
Fu, et al. (1991) Variation of the CGG Repeat at the Fragile X Site Results in Genetic Instability: Resolution of the Sherman Paradox. Cell, Vol 67: 1047-1058. Oostra, et al. (1993) Guidelines for the Diagnosis of Fragile X Syndrome. J. Med. Genetics, Vol 30: 410-413. Nolin, et al. (1996) Familial Transmission of the FMRI CGG Repeat. AM. J. Human Genetics, Vol 59: 1252-1261. Zhong, et al. (1996) Fragile X "Gray Zone" Alleles: AGG Patterns, Expansion Risks, and Associated Haplotypes. Am. J. Med. Genetics, Vol 64: 261-265. De Vries, et al. (1996) Mental Status of Females with an FMR1 Gene Full Mutation. Am. J. Human Genetics, Vol 58: 1025-1032. |
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| Contact Information: | UIDL Client Services Monday-Friday - 8:00 am-6:30 pm CST Saturday - 8:00 am-1:00 pm CST Phone - 866-844-2522 Fax - 319-384-7213 Technical Test Information Molecular Pathology Laboratory 319-384-9568 |