Genetic Analysis of Human First Trimester Trophoblast in Ongoing Pregnancies

DESCRIPTION (provided by applicant): Prenatal diagnosis using cells obtained from the developing conceptus can provide critical information about obstetric pathophysiology and fetal genetics. This information can be utilized to anticipate genetic disorders brought about by heredity or chromosomal errors that increase with maternal age. The most common methods of retrieving fetal tissue for prenatal diagnosis, amniocentesis and chorionic villous sampling, are invasive, with a risk of fetal loss. Additionally, they are not available before 9-14 weeks of pregnancy. However, fetal trophoblast cells migrate from the placenta into the cervix as early as 3 to 4 weeks after fertilization, when most pregnancies are first detected. The proposed investigation will build upon past success in refining a minimally invasive method to recover fetal cell from the cervix that is essentially identical to a PAP test. We can reliably collect and identfy trophoblast cells in specimens obtained by transcervical sampling (TCS) from pregnant women early in the first trimester. Furthermore, we can isolate the trophoblast cells free from resident maternal cervical cells by immunomagnetic affinity separation to be used for genetic analysis of fetal DNA. In Specific Aim 1, the fetal DNA will be validated by short tandem repeat (STR) profiling and comparison to blood samples from the mother and corresponding neonate (N=50). Single cell approaches adapted from preimplantation genetic screening will identify individual fetal cells in heterogeneous isolates. Microgram quantities of DNA from individual cells generated by whole genome amplification (WGA) will be used for STR profiling and saved for further genetic analysis. Structural chromosomal anomalies cause birth defects and are a high priority for prenatal genetic testing. In Specific Aim 2, the utility of trophoblast cells obtainedby TCS for chromosomal analysis will be examined by considering the hypothesis that these placenta-derived cells accurately report the status of chromosomes in those fetal cells that develop to form the neonate. Amplified fetal DNA from samples studied in Aim 1 will be compared to neonatal DNA by comparative genomic hybridization to determine the numerical status of all 24 human chromosomes. These studies will establish the limitations of TCS for providing reliable genetic information on the fetus during the first trimester. The methodologies developed in this investigation could eventually establish clinical tests that use TCS, providing information on the genetic status of the fetus before development has progressed beyond the first two months.