Clinical, Cytogenetic and Molecular Cytogenetic Outcomes of Cell-Free DNA Testing for Rare Chromosomal Anomalies.

The scope of cell-free DNA (cfDNA) testing was expanded to the genome, which allowed screening for rare chromosome anomalies (RCAs). Since the efficiency of the test for RCAs remains below the common aneuploidies, there is a debate on the usage of expanded tests. This study focuses on the confirmatory and follow-up data of cases with positive cfDNA testing for RCAs and cases with screen-negative results in a series of 912 consecutive cases that underwent invasive testing following cfDNA testing. Chorion villus sampling (CVS), amniocentesis (AS), fetal blood sampling, and term placenta samples were investigated using classical cytogenetic and molecular cytogenetic techniques. Out of 593 screen-positive results, 504 (85%) were for common aneuploidies, 40 (6.7%) for rare autosomal trisomies (RATs), and 49 (8.3%) for structural chromosome anomalies (SAs). Of the screen-positives for RATs, 20 cases were evaluated only in fetal tissue, and confined placental mosaicism (CPM) could not be excluded. Among cases with definitive results (n = 20), the rates of true positives, placental mosaics, and false positives were 35%, 45%, and 10%, respectively. Among screen-positives for SAs, 32.7% were true positives. The confirmation rate was higher for duplications than deletions (58.3% vs. 29.4%). The rate of chromosomal abnormality was 10.9% in the group of 256 screen-negatives with pathological ultrasound findings. This study provides further data to assess the efficiency of expanded cfDNA testing for RATs and SAs. The test efficiency for cfDNA seems to be higher for duplications than for deletions, which is evidence of the role of expert ultrasound in identifying pregnancies at increased risk for chromosome anomalies, even in pregnancies with screen-negatives. Furthermore, we discussed the efficiency of CVS vs. AC in screen-positives for RATs.

Follow-Up Studies of cf-DNA Testing from 101 Consecutive Fetuses and Related Ultrasound Findings.

PURPOSE: To determine the true- and false-positive rates of cf-DNA testing in a cohort of patients from tertiary care centers and assess the impact of ultrasound examinations in pregnancy management. MATERIALS AND METHODS: Clinical, cytogenetic and ultrasound data of 101 consecutive fetuses were collected retrospectively. Cases were classified into five groups according to the ultrasound findings. Karyotyping, interphase FISH and microarray techniques were used for follow-up studies. RESULTS: The overall false-positive rate was low for trisomy 21 (T21, 8.2 %), but significantly higher for trisomy 18 (T18, 40 %), monosomy X (MX, 50 %), X/Y trisomies (57.1 %), trisomy 13 (T13, 71.4 %). While single cases of trisomy 16, trisomy 22 and 8q duplication positive in cf-DNA were confirmed, 3 microdeletions (1p36 and two 22q11.2) were not. About 75 % of confirmed T21's and all confirmed T18 and T13 had major markers and/or malformations. While false-negative cases (two T21, one T18 and one T13) were identified due to abnormal ultrasound findings, all false-positive cases were normal sonographically. Ultrasound findings of confirmed trisomy 16, 22, dup8q, monosomy X and other X/Y aneuploidies were unspecific. Term placenta studies were helpful to assess the role of confined mosaicism in unconfirmed cf-DNA test results. A vanishing twin has been observed as the likely cause of one false-positive T18. CONCLUSION: Our study contributes clinical data on discrepant cf-DNA testing results, corroborates the need for confirmational invasive testing and underscores the benefit of expert ultrasound in the prevention of fatal diagnostic errors.

Corpus callosum agenesis in trisomy 8p11.23 and monosomy 4q34 because of maternal translocation.

We report on a 3-year-old boy with partial trisomy 8 p11.23-->pter and partial monosomy 4q34-->qter, associated with developmental delay, complete agenesis of the corpus callosum, and mild dysmorphic features. Although agenesis of the corpus callosum is not a rare finding among chromosomal abnormalities, partial trisomy 8p together with partial monosomy 4q, resulting from a maternal translocation, was not previously reported, to the best of our knowledge.