Objective:To investigate the power and prenatal diagnosis strategies of cell-free fetal DNA (cffDNA) testing for chromosomal aneuploidy screening apart from trisomy-13/18/21.Methods:This study collected the clinical data of three cases at high risk of trisomy-16 indicated by cffDNA testing in Hunan Provincial Maternal and Child Health Care Hospital from March 2019 to March 2020. Results of the conventional G-banding karyotype analysis of amniotic fluid, single nucleotide polymorphism array (SNP-array) and low-coverage massively parallel copy number variation sequencing (CNV-seq) of placenta/fetal skin samples were analyzed.Results:(1) cffDNA testing results suggested that case 1-3 were at high risk of trisomy-16 and the Z values of chromosome 16 were 20.57, 24.88 and 17.87, respectively. (2) Karyotype analysis of amniotic fluid samples did not identify any abnormalities in Case 1 and 2, while SNP-array revealed a 19.2 Mb and 23.0 Mb heterozygous deletion at 16p13.3p12.3 and 16q22.1q24.3 in Case 1, and a 16.0 Mb loss of heterozygosity at 16q22.3q24.3 in Case 2. Case 3 had a mosaicism karyotype of 47,XY,+16[3]/46,XY[97] and SNP-array analysis showed no heterozygous deletion greater than 5 Mb or copy number variation. (3) Ultrasonography indicated fetal growth restriction in Case 1 and 2 and fetal death in Case 3. All three pregnancies were terminated. CNV-seq analysis of placental tissue in the center of both fetal and maternal side revealed mosaic trisomy 16, with the copy numbers of chromosome 16 of 2.56/2.70, 2.73/2.82, 2.80/2.81, respectively. However, no copy number variation was detected in Case 1 or 2 by CNV-seq analysis of fetal skin tissues. Conclusions:cffDNA testing has a certain power in detecting trisomy-16 apart from trisomy-13/18/21. For high-risk cases of trisomy-16 indicated by cffDNA testing, SNP-array analysis combined with karyotype analysis is suggested to rule out low-level mosaicism and loss of heterozygosity.

Objective:To analyze the costs and effectiveness of five common screening modes and genetic screening for thalassemia in China in order to find the optimal way and provide evidence for the implementation of thalassemia prevention and control projects in Hunan Province.Methods:From June 2020 to April 2021, 12 971 couples from 14 cities and autonomous prefectures in Hunan Province were selected as the study population. The diagnosis of thalassemia was based on the results of genetic testing. Results of routine blood test and hemoglobin electrophoresis were collected and analyzed. The efficacy of five screening modes, at the cut-off value of <80 fl or 82 fl for the mean corpuscular volume (MCV), was analyzed by positive predictive value, negative predictive value, Jorden index and cost-effectiveness ratio. Sensitivity analysis was used to assess the feasibility of genetic screening at different costs after fixing the costs of routine blood and hemoglobin electrophoresis. The five thalassemia screening models are as follows: Mode 1: The woman had a blood routine test first. If the result was positive, the spouse required a blood routine test. If both results were positive, a thalassemia gene test should be offered to the couple. Mode 2: Both husband and wife were screened by blood routine and hemoglobin electrophoresis. If one or both of them were positive, both would be tested for thalassemia gene. Mode 3: The couple received blood routine tests initially. If either was positive, both should receive hemoglobin electrophoresis testing. If either was positive, both parties will conduct thalassemia gene testing. Mode 4: The woman was screened by blood routine and hemoglobin electrophoresis. If any one of them was positive, the woman would be tested for thalassemia gene. If the gene test result was positive, the spouse should receive thalassemia gene. Mode 5: Both spouses conducted a blood routine test. If either was positive, both would conduct hemoglobin electrophoresis test. If both were positive, both spouses should receive thalassemia gene testing. Gene testing mode: The woman would be tested for thalassemia, and her spouse would have thalassemia test too if her result was positive.Results:When using MCV<80 fl as the cut-off for diagnosing thalassemia, the Youden indices of the five prenatal screening modes in Hunan Province were 0.551, 0.639, 0.898, 0.555 and 0.356, while when using MCV<82 fl as the cut-off, the Youden indices were 0.549, 0.629, 0.851, 0.548 and 0.356. When the MCV cut-off value was <80 fl, the missed diagnosis rates of the five screening modes were 44.44%, 0.00, 0.00, 18.52% and 62.96%, and the cost-effectiveness ratios were 21 709, 250 939, 76 870, 138 463 and 92 860 yuan (RMB)/couple, respectively. When the price of genetic testing was lower than 55 yuan (RMB), the cost-effectiveness ratio of genetic screening was lower than that of Mode 3.Conclusions:MCV<80 fl can be considered as the positive criteria in blood routine screening for thalassemia in Hunan Province, and the cost-effectiveness ratio of Mode 3 (the couple received blood routine tests initially. If either was positive, both should receive hemoglobin electrophoresis testing. If either was positive, both parties will conduct thalassemia gene testing) is the best. Genetic screening has certain advantages with the decreasing price.