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Article
July 1993

Molecular-Clinical Correlations in Children and Adults With Fragile X Syndrome

Author Affiliations

From the Child Development Unit (Mss Staley, Hull, Riddle, and O'Connor and Drs Mazzocco and Hagerman), Molecular Genetics Laboratory (Drs Wilson and Taylor), and Cytogenetics Laboratory (Dr McGavran), The Children's Hospital, and the Department of Pediatrics, University of Colorado Health Sciences Center (Drs Weiner and Hagerman), Denver, Colo; and Mayo Medical Laboratory, Department of Laboratory Medicine, Rochester, Minn (Drs Thibodeau and Snow).

Am J Dis Child. 1993;147(7):723-726. doi:10.1001/archpedi.1993.02160310025011
Abstract

• Introduction.  —Fragile X syndrome is the most commonly known inherited form of mental retardation. The intellectual abilities range from a normal IQ with learning disabilities to severe mental retardation. In males, there is a tendency for IQ decline in childhood. The purpose of this study was to correlate variations of the molecular cytosine guanine guanine (CGG) amplification in the fragile X mental retardation-1 (FMR-1) gene with the clinical findings, including IQ and physical features.

Methods.  —Full-scale IQ and cytogenetic results in 116 individuals with the FMR-1 mutation were studied. The IQ testing was performed with age-appropriate standardized tests. Physical features were summarized in a physical index score for each patient. The FMR-1 results were determined with the OX1.9 probe and the following system was used: P1 indicates premutation; P2, large premutation to small full mutation; P3, full mutation; and P4, mosaic.

Results/Conclusions.  —The findings showed that those females with a small insert in the P1 range had a significantly higher IQ than other heterozygotes (P2, P3, and P4 categories). P4 males had a significantly higher IQ than P2 or P3 males. In cross-sectional age comparisons, the slope of the IQ decline was greater in P2 males than in P4 or P3 males.(AJDC. 1993;147:723-726)

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