Glial fibrillary acidic protein in amniotic fluids from pregnancies with fetal neural tube defects

Amniotic fluid glial fibrillary acidic protein (AF-GFAP), a biomarker of open neural tube defects

OBJECTIVE

Neural tube defects (NTDs) are usually identified by ultrasonography and confirmed by alpha-fetoprotein (AFP) assay and acetylcholinesterase (AchE) electrophoresis in amniotic fluid. Yet, both of these biomarkers can be found positive in other etiologies. Here, amniotic fluid glial fibrillary acidic protein (AF-GFAP), which was identified by a proteomic study, is shown to be a useful biomarker for NTD diagnosis.

METHOD

Amniotic fluid glial fibrillary acidic protein was measured by an ELISA assay in 138 cases of NTDs. Seventy samples from normal pregnancies used as controls and 27 samples giving false positive or false negative results either for AchE or AFP and corresponding to fetal death (n = 8), gastroschisis (n = 8), and unexplained etiologies (n = 11) were also tested.

RESULTS

Whatever the gestational age, GFAP was below 0.2 ng/mL in control samples, whereas 99.1% of open NTDs (29/29 in the anterior NTD group and 80/81 in the spina bifida group) were above this threshold. Closed NTDs were all negative (28/28). None of the other samples tested were positive, except in case of fetal death (8/8).

CONCLUSIONS

Amniotic fluid glial fibrillary acidic protein is a sensitive biomarker for open NTD diagnosis with a good negative predictive value for closed NTD. Compared with AFP and AchE, our results indicate that AF-GFAP alone is more efficient than this classical association.

Amniotic fluid levels of glial fibrillary acidic protein in fetal rats with retinoic acid induced myelomeningocele: a potential marker for spinal cord injury

OBJECTIVE

The objective of this study was to determine whether amniotic fluid levels of glial acidic fibrillary protein (GFAP) would reflect myelomeningocele-related neurodegeneration in the rat model of retinoic acid-induced myelomeningocele, which is a model that is very similar to human myelomeningocele and develops the entire spectrum of disease severity including features of the Chiari II malformation.

STUDY DESIGN

Time-dated (embryonic day 10) pregnant Sprague-Dawley rats were gavage fed 60 mg/kg/bodyweight retinoic acid that had been dissolved in olive oil or olive oil alone. Myelomeningocele, retinoic acid-exposed no myelomeningocele, and control fetuses were harvested at specific time points throughout gestation. A standard set of pinching tests was performed to interrogate the sensorimotor reflex arc of hindpaws and tails. Amniotic fluid-GFAP levels were analyzed by standard enzyme-linked immunosorbent assay techniques.

RESULTS

Amniotic fluid-GFAP levels were similar between groups at embryonic days 14, 16, and 18, respectively. Compared with control fetuses, amniotic fluid GFAP levels were significantly increased in myelomeningocele fetuses at embryonic days 20 and 22 (P < .001). Defect size (P < .001), presence of clubfoot deformity (P = .0004), and absence of sensorimotor function (P < .01) at embryonic day 22 correlated with amniotic fluid-GFAP levels.

CONCLUSION

Amniotic fluid-GFAP levels appear to correlate with spinal cord injury as gestation proceeds in fetal rats with myelomeningocele.

Amniotic fluid brain-specific proteins are biomarkers for spinal cord injury in experimental myelomeningocele

Myelomeningocele (MMC), the most severe form of spina bifida (SB), causes neurological deficit. Injury to the spinal cord is thought to begin in utero. We investigated whether brain-specific proteins (BSPs) would enable us to monitor the development of MMC-related tissue damage during pregnancy in an animal model with naturally occurring SB (curly tail/loop tail mouse; n = 256). Amniotic fluid levels of neurofilament heavy chain (NfH), glial acidic fibrillary protein (GFAP) and S100B were measured by standard ELISA techniques. The amniotic fluid levels of all BSPs were similar in SB and control mice on embryonic day (E) 12.5 and 14.5, whereas a significant increase was observed for GFAP in SB mice on E16.5. Levels of all BSPs were significantly increased in SB mice on E18.5. The rapid increase in GFAP, paralleled by a moderate increase in NfH and S100B, suggests that spinal cord damage starts to accelerate around E16.5. The macroscopic size of the MMC was related to NfH level on E16.5 and E18.5, suggesting that axonal degeneration is most severe in large MMC. Amniotic fluid BSP measurements may provide important information for balancing the risks and benefits to mother and child of in utero surgery for MMC.

An ELISA for glial fibrillary acidic protein

Glial fibrillary acidic protein (GFAP) is the major intermediate filament protein of the astrocyte, and body fluid levels of GFAP are an important tool for estimating astrogliosis and astrocytic activation in vivo. This paper presents a new sandwich ELISA allowing quantification of GFAP(SMI26) from the cerebrospinal fluid (CSF). The sensitivity of the GFAP(SMI26) ELISA is 5 pg/ml with a recovery of 94% and a mean within- and between-batch precision of 6% and 10%, respectively. The upper reference value for CSF GFAP(SMI26) levels (9 pg/ml) was defined as the 95% cumulative frequency from 315 CSF samples. Based on this cut-off, a significantly higher proportion of patients with subarachnoid hemorrhage (100%), traumatic brain injury (100%), dementia (76%) and normal pressure hydrocephalus (85%) had pathologically elevated CSF GFAP(SMI26) levels compared to patients with peripheral nervous system disorders (0%). In a critical review of the literature, we compare the analytical and clinical sensitivity of previous GFAP ELISA methods with particular reference to patients with dementia.

Antenatal detection of neural tube defects: comparison of biochemical and immunofluorescence methods

The aim of this study was to determine whether identification of glial cells in amniotic fluid samples could form a useful supplementary test in the antenatal diagnosis of neural tube defects (NTDs). In a 5-year study, 1452 samples of middle trimester amniotic fluid were examined blind to the results of other antenatal diagnostic tests and to the outcome of pregnancy. Reason of amniocentesis included raised serum alpha-fetoprotein (329), previous NTD (73), and a family history of NTDs (71). Duplicate cytospin preparations were stained with Giemsa and an antibody to glial fibrillary acidic protein (GFAP), and on this basis a prediction of fetal NTD status was made which was not communicated to clinicians. Subsequent management of pregnancies was influenced only by the results of routine antenatal testing for NTDs. Twenty cases of NTDs occurred among the 1406 cases in which the outcome was subsequently known. Of these 20 cases, only five (four anencephalic, one spina bifida) were correctly predicated by immunofluorescent identification of GFAP-positive cells in the amniotic fluid. The remaining 15 cases (two anencephalic, 13 spina bifida) were not so identified. In a further 18 cases, apparently GFAP-positive cells were identified in the absence of NTDs. We conclude that GFAP immunofluorescence examination of routine amniocentesis samples of amniotic fluid is not a useful predictive test for NTDs.

Value of glial fibrillary acidic protein determination in amniotic fluid for prenatal diagnosis of neural tube defects

Glial fibrillary acidic protein (GFAp), an intracellular protein specific to astrocytes of the central nervous system, was determined by 2-site immunoradiometric assay in amniotic fluid from 78 pregnancies with a normal, and 100 with an abnormal outcome. GFAp was not detectable in any of the normal pregnancies, but there were measurable, and so raised, levels in 23 out of 25 cases of anencephaly and 4 out of 7 cases of spina bifida, which therefore allowed prenatal diagnosis. GFAp was also increased in 4 of 6 cases of fetal intrauterine death, but not in other congenital malformations associated with elevated alphafetoprotein levels or abnormal acetylcholinesterase banding pattern, such as exomphalos, other gastrointestinal malformations or renal abnormalities. GFAp is therefore specific for diagnosing open neural tube defects. The determination of GFAp in amniotic fluid was slightly less efficient overall than AFP for the prenatal diagnosis of neural tube defects, but can be a useful ancillary test and has the advantage of specificity.