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Genetics

Poster Session 2

(563) Cell free DNA whole genome (cfDNA-WG) in clinical practice: a single center 6-year experience

Tuesday, February 13, 2024
3:30 PM – 5:00 PM  
Location: Prince George's Exhibit Hall CDE, Lower Atrium Level
Objective: At our institution, cell free DNA whole genome (cfDNA-WG) is offered to patients who decline diagnostic testing after genetic counseling for abnormal fetal ultrasound findings.  cfDNA-WG detects > 7 MB duplications and deletions across the genome, whereas diagnostic testing considers any aberration > 1 MB abnormal.  We describe cfDNA-WG test performance in our population.

Study Design: We performed a retrospective analysis of subjects identified through our genetic counseling database.  Our study group was subjects with abnormal fetal ultrasound findings in a singleton pregnancy. Descriptive data was abstracted via chart review.  When diagnostic testing was also performed, this was compared to cfDNA-WG results.

Results: We identified 356 subjects with cfDNA-WG results. 40 had normal sonographic exams and were excluded.  In the 316 subjects remaining, ultrasound findings included multiple congenital anomalies (n = 107), isolated anomaly (n = 105), isolated soft marker (n = 48), thickened nuchal translucency (n = 46), fetal growth restriction (n = 6), and placental abnormalities (n = 3).  cfDNA-WG results were abnormal in 20 cases (6.3%). Most abnormal results (90%) were whole-chromosome aneuploidies: T21 (n = 9), T18 (n = 5), T13 (n = 1), and monosomy X (n = 3). Two other abnormal results included one T22 and one microdeletion (22, q11.2-q11.2). Of the 316 subjects, 35 (11.1%) had diagnostic testing which revealed 4 discordant results where cfDNA-WG was not reflective of diagnostic results (Figure 1), including Trisomy 8 and two single gene disorders (neurofibromatosis 1, CFAP298 gene mutation). In addition, there was a case of low mosaicism for T13, not confirmed in the fetus. 

Conclusion: In this cohort of subjects who had cfDNA-WG, 6.3% had abnormal testing, most of which could be identified on a standard cfDNA test.  There were 3 cases with normal cfDNA-WG in fetuses with significant genetic disorders, giving patients false reassurance and limiting the value of normal results. Our data can aid in patient counseling on benefits and limitations of this test.