Reduction in the number of CGG repeats on the FMR1 gene in carriers of genetic disorders versus noncarriers

OBJECTIVE: CGG repeat expansion on the fragile X mental retardation 1 (FMR1) gene is used to diagnose fragile X syndrome. Previous studies have discussed the correlation between the number of CGG repeats and its associated phenotypic components. The objective of this study is to determine whether the number of CGG repeats differ between carriers of genetic disorders versus noncarriers. METHODS: We performed a retrospective chart review of 2867 patients who received genetic screening at our fertility clinic between June 2013 and July 2015. The number of CGG repeats on allele 1 and allele 2 on the FMR1 gene was collected and it was specified whether the patient was a carrier or a noncarrier of a specific mutation. Patients with CGG repeats greater than or equal to 45 were excluded from the study. RESULTS: Carriers (n=759) had a reduced number of repeats compared to noncarriers (n=2024) on allele 1 (p=.03), allele 2 (p=.02) and the average of both alleles (p=.01). Additionally, the number of CGG repeats from the ten most carried diseases from the cohort were used and tested individually for clinical significance against the number of repeats in the noncarriers. A reduction in repeats was shown in several mutations and a few were outliers. CONCLUSION: Our results demonstrate that there is a significant reduction in the number of CGG repeats in carriers of genetic mutations. A larger scale study of disease carrying patients would be beneficial.