Journal
GENETICS IN MEDICINE
Volume 9, Issue 1, Pages 46-51Publisher
LIPPINCOTT WILLIAMS & WILKINS
DOI: 10.1097/GIM.0b013e31802d833c
Keywords
Fragile X syndrome; Martin Bell syndrome; triplet repeat expansion FMR1; X-linked dominant disease
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Purpose: To examine the data from over 119,000 Fragile X Syndrome tests and 307 prenatal tests to detect unsuspected findings and obtain clinical data when indicated to optimize genetic counseling. Methods: A proprietary database containing 119,232 consecutive postnatal and 307 prenatal FXS tests performed between November 2, 1992 and June 1, 2006 was queried. Results: The distribution of normal FMR1 alleles was a bimodal distribution with a major peak at 30 repeats and a minor peak at 21 repeats. Of 59,707 tests performed for males, 1.4% had a fully expanded and methylated FMR1 allele. Of 59,525 tests performed for females, 0.61% had an affected FMR1 allele, and 1.7% had a premutation FMR1 allele for a total carrier frequency of 1.3%. When fetuses inherited an expanded maternal allele, the risk of expansion to a full affected allele was 0%, 5%, 30% and 100% for allele sizes of < 50, 50-75, 76-100 and > 100 repeats, respectively. Conclusions: These figures can be used for genetic counseling of patients presenting for carrier detection and prenatal diagnosis for Fragile X Syndrome.
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