Abstract
Chromosomes carrying the mutation causing the fragile X [ fra (X) ] syndrome have been shown to have an unstable DNA sequence close to or within the fragile site. The length variation is located within a DNA fragment containing a CGG trinucleotide repeat which is unstable in both mitosis and meiosis.
We have used the probe StB12.3 from the Xq27.3 region to analyze the mutations and the methylation patterns by Southern blot analysis in 21 families segregating for the fra(X) syndrome
Results: Among 40 fra(X) males all showed an abnormal pattern. Six out of 33 fra(X) negative females at risk were diagnosed as carriers using DNA analysis. Mentally impaired females showed a high degree of methylated, inactive X as compared to healthy carriers.
Conclusion: The probe StB 12.3 provides a sensitive and specific test for the presence of the fra(X) mutation. Carriers without cytogenetic expression of fra(X) can be detected. The prediction of mental impairment in female carriers can be made by the estimation of the degree of methylation of the normal chromosome.
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Malmgren, H., Steen-Bondesson, ML., Gustavson, KH. et al. METHYLATION AND MUTATION PATTERNS IN THE FRAGILE X SYNDROME. Pediatr Res 32, 621 (1992). https://doi.org/10.1203/00006450-199211000-00101
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DOI: https://doi.org/10.1203/00006450-199211000-00101