FMR1 premutation frequency in a large, ethnically diverse population referred for carrier testing.

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability and is caused by an expansion of cytosine-guanine-guanine (CGG) repeats in the FMR1 gene. Female premutation allele carriers (55-200 CGG repeats) are at risk to have an affected child. Currently, specific population-based carrier screening for FXS is not recommended. Previous studies exploring female premutation carrier frequency have been limited by size or ethnicity. This retrospective study provides a pan-ethnic estimate of the Fragile X premutation carrier frequency in a large, ethnically diverse population of women referred for routine carrier screening during a specified time period at Progenity, Inc. Patient ethnicity was self-reported and categorized as: African American, Ashkenazi Jewish, Asian, Caucasian, Hispanic, Native American, Other/Mixed/Unknown, or Sephardic Jewish. FXS test results were stratified by ethnicity and repeat allele category. Total premutation carrier frequency was calculated and compared against each ethnic group. A total of 134,933 samples were included. The pan-ethnic premutation carrier frequency was 1 in 201. Only the Asian group differed significantly from this frequency. Using the carrier frequency of 1 in 201, a conservative pan-ethnic risk estimate for a male fetus to have FXS can be calculated as 1 in 2,412. This risk is similar to the highest ethnic-based fetal risks for cystic fibrosis and spinal muscular atrophy, for which population-wide screening is currently recommended. This study adds to the literature and supports further evaluation into specific population-wide screening recommendations for FXS.

Clinical experience with multigene carrier panels in the reproductive setting.

OBJECTIVES: Expanded carrier testing is acknowledged as an acceptable strategy for carrier testing by the American College of Obstetrics and Gynecology. Limited studies have investigated positivity rates of expanded carrier panels. We describe our experience with 3 commercial laboratory panels varying in size from 3 to 218 disorders. METHODS: We reviewed outcomes for 3 multigene carrier screening panels: trio (3 diseases), standard (23 diseases), and global (218 diseases). All panels used targeted genotype analysis of preselected mutations via next-generation sequencing. We calculated positivity rates for each panel. RESULTS: Positivity rates were 7.2% for Preparent Trio, 13.2% for Preparent Standard, and 35.8% for Preparent Global. The most frequent positive results in the global panel were (in descending order): abnormal hemoglobin electrophoresis, familial Mediterranean fever, cystic fibrosis, fragile X, glucose-6-phosphate dehydrogenase deficiency, alpha-thalassemia, and nonsyndromic hearing loss. CONCLUSIONS: While genetic diseases are individually rare, they are cumulatively common. Our experience illustrates that, with a panel of 218 diseases, the likelihood of identifying a carrier can be as high as 36%. Understanding panel positivity rates is one important factor for providers when choosing the right test for their practice, setting appropriate expectations for patients, and planning for follow-up counseling.