Fragile X Syndrome

SYD: 28




Fragile X Syndrome

Description: Fragile X syndrome is the most common cause of inherited mental retardation, seen in approximately one in 1,200 males and one in 2,500 females. Males with fragile X syndrome usually have mental retardation and often exhibit characteristic physical features and behavior [Hagerman and Silverman, 1991; Warren and Nelson, 1994]. Affected females exhibit a similar, but usually less severe phenotype.The syndrome is associated with the expansion (excessive repetition) of a single trinucleotide gene sequence (CGG) on the X chromosome, and results in a failure to express the FMR-1 protein which is required for normal neural development. There are four generally accepted forms of Fragile X syndrome which relate to the length of the repeated CGG sequence; Normal (29-31 CGG repeats), Premutation (55-200 CGG repeats), Full Mutation (more than 200 CGG repeats), and Intermediate or Gray Zone Alleles (40 - 60 repeats). The diagnosis of fragile X syndrome was originally based on the expression of a folate-sensitive fragile site at Xq27.3 (FRAXA) induced in cell culture under conditions of folate deprivatio.Also, interpretation of the cytogenetic test for fragile X syndrome is complicated by the presence of other fragile sites in the same region of the X chromosome (FRAXD, FRAXE, and FRAXF).


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Developmental anomalies

Listed in the combination's profile :


There are no developmental anomalies for this combination.

Observed in MDB cases:


There are no developmental anomalies for this combination.
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