Replacing Alpha-Fetoprotein With Alpha-Fetoprotein-L3 Increases the Sensitivity of Prenatal Screening for Trisomy 21

Role of Alpha-Fetoprotein in the Pathogenesis of Cancer

Alpha-fetoprotein (AFP) belongs to the albuminoid protein family and is considered as the fetal analog of serum albumin. This plasma protein is initially synthesized in the fetal liver and yolk sac and shows a maximum peak near the end of the first trimester. Later, concentrations begin to decline prenatally and drop precipitously after birth. This protein has three key ligand-binding pockets for interactions with various biomolecules. It contains multiple phosphorylation and acetylation sites for the regulation of physiological and pathophysiological states. High serum AFP titer is an established biomarker for yolk sac, embryonal and hepatocellular carcinoma. The present review critically analyzes the chemical nature, receptors, clinical implications, and therapeutic aspects of AFP, underpinning the development of different types of cancer.

Diagnostic value of maternal alpha-fetoprotein variants in second-trimester biochemical screening for trisomy 21 and 18

To evaluate the clinical predictive value of serum alpha-fetoprotein variants (AFP-L2, AFP-L3) in combination with maternal serum prenatal screening biomarkers in predicting fetal trisomy 21 and trisomy 18. We analyze the data of singleton pregnant women at 15–20⁺⁶ weeks of 731,922 gravidas from October 2007 to September 2019. The research objects were separated into the following groups: control (n = 569), trisomy 21 (n = 116), and trisomy 18 (n = 52). The cases were diagnosed by chromosomal karyotypic analysis of amniotic fluid cells. Level of AFP-L2 and AFP-L3 were detected in maternal serum among control women and patients. Receiver operator characteristic analysis, detection rate, false positive rate, false negative rate, positive predictive value, negative predictive value, positive likelihood ratio and negative likelihood ratio, comprehensive discriminant improvement, net weight classification improvement, decision curve analysis and Hosmer–lemeshow (H-L) test were used to investigate the predictive value of free β-hCG, AFP, AFP-L2 and AFP-L3 on the risk models of trisomy 21, 18. There was a statistically significant difference in maternal serum AFP-L2 and AFP-L3 multiple of the median (MoM) among the trisomy 21, trisomy 18, and control groups. The AUCs of AFP-L2 and AFP-L3 for the screening trisomy 21 and trisomy 18 fetus were 0.785, 0.758 and 0.775, 0.754. According to ROC, the optimal cut-off values of AFP-L2 and AFP-L3 for predicting trisomy 21 and trisomy 18 fetuses all were 1.09 MoM and 1.30 MoM, respectively. The risk-calculation model constructed by AFP-L2 + AFP-L3 MoM manifested better efficiency than the original single-value truncation method using AFP MoM alone. Compared with different modeling methods, the AUC of trisomy 21 fetuses predicted by AFP-L2 + AFP-L3 + free β-hCG achieved an optimal value (0.938), while the AUC of trisomy 18 fetus predicted by AFP-L2 + free β-hCG was the best (0.991). Compared with AFP, the IDI of AFP-L2 or AFP-L3 alone increased 9.56% and 12.34%; the NRI increased 26.50% and 26.70 in predicting trisomy 21. For trisomy 18, the IDI of AFP-L2 or AFP-L3 alone declined with 8.12% and 1.52%; the NRI declined with 13.84% and 8.54%. In the combined model, the model with best detection rate, false positive rate and positive likelihood ratio was AFP-L2 + AFP-L3 + free β-hCG, followed by AFP-L2 + free β-hCG and AFP-L3 + free β-hCG, and finally AFP + free β-hCG. Maternal serum AFP-L2 and AFP-L3 in the second trimester is a good marker for screening trisomy 21 and trisomy18 with high sensitivity and specificity. The combined screening results are better than the single marker, and the efficiency of AFP-L2 + AFP-L3 + free β-hCG is the best.

Construction and predictive value of risk models of maternal serum alpha-fetoprotein variants and fetal open neural tube defects

The correlation of maternal serum alpha-fetoprotein (AFP) variants (AFP-L2, AFP-L3), free beta-human chorionic gonadotropin (free β-hCG), and open neural tube defects (ONTDs) during the second trimester, and the screening efficiency of different risk models remain indistinct. We conducted a retrospective case-control study, and studied 57 pregnant women with ONTD fetuses and 569 pregnant women with normal fetuses. The receiver operating characteristic curve method indicated the best cutoff value and area under the curve (AUC). The predictive value of ONTD risk models by free β-hCG, AFP, AFP-L2, and AFP-L3 was investigated via integrated discrimination improvement (IDI), net reclassification improvement (NRI), and decision curve analysis (DCA). Compared to the control group, AFP, AFP-L2, and AFP-L3 levels were significantly higher, while free β-hCG level was significantly lower in the study group. The triple-index model of free β-hCG + AFP-L2 + AFP-L3 and the dual-index model of AFP-L2 + AFP-L3 showed the best predictive values, respectively (AUC = 0.905; AUC = 0.885). The order of the single-index model AUCs was AFP-L3 > AFP-L2 > AFP > free β-hCG. The negative predictive value, false positive rate, and negative likelihood ratio of AFP-L2, AFP-L3 alone, or combined with free β- hCG were better than those of AFP alone; however, the positive likelihood ratio was the opposite. The replacement of AFP by AFP-L2 or AFP-L3 combined with free β-hCG increased the IDI and NRI for predicting ONTD. The top five DCAs were AFP-L2 + free β-hCG, free β-hCG, AFP-L3, AFP + free β-hCG, and AFP. Indicators of maternal serum free β-hCG, AFP-L2, and AFP-L3 in the second trimester exhibited high sensitivity and specificity screening for ONTD fetuses. Risk models constructed using AFP-L2 + AFP-L3 and AFP-L2 + AFP-L3 + free β-hCG demonstrated better screening efficiency.

Effectiveness of alpha-fetoprotein variants L2 and L3 as substitutes of alpha-fetoprotein in screening for fetal Trisomy 18

OBJECTIVE

To evaluate the effectiveness of alpha-fetoprotein variants (AFP-L2, AFP-L3) in fetal screening for Trisomy 18 in place of alpha fetoprotein (AFP).

METHODS

A retrospective case-control study was conducted. Collectively, 39 pregnant women bearing Trisomy 18 fetuses and 48 pregnant women with clinically normal and healthy fetuses were included. The serum AFP-L2 and AFP-L3 concentrations were detected by enzyme-linked immunosorbent assays. The likelihood ratio method and Python software were used to construct the risk model with AFP, free β-hCG, AFP-L2, and AFP-L3 to predict Trisomy 18. Receiver operating characteristic (ROC) curves were used to determine the optimal cutoff value, while the area under the curve (AUC) was used to assess the screening performance of AFP-L2 and AFP-L3 for fetal Trisomy 18.

RESULTS

Compared to values observed for the control group, AFP-L2 and AFP-L3 concentrations which were significantly higher (both p< .001) in pregnant women with Trisomy 18 fetuses were 7.95 ± 3.57 ng/mL and 2.53 ± 1.80 ng/mL, respectively. Comparisons across multiple modeling methods showed that the highest AUC of screened Trisomy 18 fetuses (0.992, 0.986, and 0.976) was yielded by AFP-L2 + AFP-L3 + free β-hCG, AFP-L2 + free β-hCG, and AFP-L3 + free β-hCG, with a sensitivity of 1.000 indicated in both instances. In different modeling methods, the order of AUC values was AFP-L2 + AFP-L3 + free β-hCG > AFP-L2 + free β-hCG > AFP-L3 + free β-hCG > AFP + free β-hCG.

CONCLUSIONS

AFP-L2 and AFP-L3 showed higher sensitivity and specificity as substitutes for AFP in screening Trisomy 18. These two markers indeed improved the screening efficiency and reduced the false positive rate, when compared with AFP only.