Molecular-intelligence correlations in young fragile X males with a mild CGG repeat expansion in the FMR1 gene.

American journal of medical genetics

PubMedID: 8844064

Steyaert J, Borghgraef M, Legius E, Fryns JP. Molecular-intelligence correlations in young fragile X males with a mild CGG repeat expansion in the FMR1 gene. Am J Med Genet. 1996;64(2):274-7.
Several mechanisms can explain the occurrence of full-mutation fragile X males with an IQ level above -2 SD below mean, also called "high-functioning fragile X males." Incomplete methylation of the CpG island at the 5' end of the FMR1 gene is one of these mechanisms. The present study describes the physical and behavior phenotypes in 7 fragile X boys with CGG repeat insertions in the FMR1 gene between 600-2,400 base pairs. The degree of methylation at the FMR1-associated CpG island ranges in peripheral blood lymphocytes from 0-95%. Subjects with a low degree of methylation at this site have mild or absent physical characteristics of the fragile X syndrome, while subjects with a high degree of methylation at this site have more severe physical characteristics. In this range of CGG repeat insertion (600-2,400 base pairs), the degree of methylation at the FMR1-associated CpG island is a good predictor of intelligence, while CGG repeat insertion length is not.