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Males with fragile X syndrome may have a recognizable facial pattern with a long face, protruding ears, and a large head.

Some males with fragile X have joint laxity. After puberty, males develop macroorchidism. Boys may have characteristic behaviors that vary with age: young children may have autistic-like features, hyperactivity or tantrums. Older children may have poor eye contact, shyness, and attention problems.

Females with fragile X may have a variable clinical presentation due to X-inactivation. Intellectual disability in females is typically mild. Other clinical findings and behaviors seen in males with fragile X have also been seen in females, with milder presentation and lower frequency.

Fragile X syndrome maps to the FMR1 gene on the X chromosome and is associated with a triplet (CGG) repeat expansion in the promoter of the FMR1 gene. CGG expansion leads to methylation and subsequent inactivation of the FMR1 gene. In individuals with normal alleles, the number of CGG repeats ranges from approximately 5-44. Individuals with approximately 55-200 CGG repeats are premutation carriers. The number of repeats in the premutation range is likely to expand in subsequent generations, particularly when passed through female meiosis. Individuals with fragile X syndrome have over 200 CGG repeats. Males with over 200 repeats are almost always affected. Mosaicism, the presence of two different sized repeats or extent of methylation, for pre and full mutation alleles has been reported in some individuals with FMR1 full CGG expansions.

Test Details

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Detection

All cases of fragile X syndrome caused by CGG expansion will be detected by this assay. Rare cases of fragile X syndrome caused by mutation of the FMR1 gene will not be detected by this assay.

Reference Range

Normal: Approximately 5-44 CGG repeats.

Intermediate: Approximately 45-54 unmethylated CGG repeats.

Premutation: Approximately 55-200 CGG repeats and methylation of expanded allele.

Affected: Over 200 CGG repeats and methylation of expanded allele.

Test Results

Turn around time: Results can be expected 15 days from the time the sample is received at the laboratory.

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Genetic carrier screening is performed through our sister laboratory, EGL Genetics Eurofins.
EGL Genetics has been providing superior, cutting-edge service for more than 47 years. Their expertise spans common and rare genetic disease testing, genomic variant interpretation, test development, and research. EGL Genetics is a CLIA-certified and CAP-accredited laboratory. They work with clients across the United States and from more than 45 countries to help improve patient diagnosis.

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