Genetic Diagnosis of Human Embryos

Article excerpt

On the top floor of the Gold Museum in Bogota, Colombia, visitors are ushered into a dark, windowless room; heavy doors are closed behind them. They stand in the darkness until gradually, like a ringed and rising sun, lights come on around them and they see they are surrounded by gold - glimmering, lustrous gold. Face masks, nose clips, amulets, and jewelry present a dazzling display of wealth and beauty.

We are at an analogous stage in medical genetics, when the lights come up and we marvel at the wealth of discoveries and what have been called "breathtaking" advances in DNA diagnosis. Experiments are underway to treat seriously ill patients with their own genetically corrected cells. More problematically, in vitro fertilization (IVF) clinics are either already analyzing egg cells for genetic defects or are poised shortly to begin DNA analysis of human embryos.

For all the worried talk about genetic engineering over the last two decades, it is surprising how quietly plans for the genetic diagnosis of human embryos have developed. The issues raised warrant careful examination: what needs are met through embryo diagnosis? Who bears responsibility for monitoring this technique? Under what overarching ethic should embryo diagnosis and, eventually, embryo therapy, be applied? What are the broader societal implications raised by the genetic diagnosis of human embryos?

The Rationale for Diagnosis

Preimplantation biopsies of human embryos are aimed at couples at high risk for having a child with a serious genetic disorder such as cystic fibrosis or Tay-Sachs disease but who will not terminate a pregnancy. A typical candidate is a couple who has one child with a serious disorder but who, for personal or religious reasons, will not undergo chorionic villus sampling (CVS) or amniocentesis and possible pregnancy termination. Traditionally, their options have been either to risk the birth of an affected child or not to conceive. Embryo biopsy gives the couple the third option of signing on with an IVF program and transferring to the wife's uterus only embryos deemed free from the genetic flaw.[1] Embryos can also be sexed in order to transfer only female embryos to couples at risk for passing a sex-linked genetic disease such as Duchenne muscular dystrophy.[2] Several IVF clinics here and abroad are offering preimplantation diagnosis or have set in motion institutional review of planned programs.[3]

Other motivations also underlie the effort to introduce embryo screening. Preimplantation diagnosis is part of a broader plan to reduce the prevalence of certain genetic diseases. Practitioners look at children with genetic disorders and, as one pediatrician said, "It is driving them crazy." He likened embryo diagnosis to the "ultimate measles vaccine": if we vaccinate children to prevent the spread of disease within a generation, should we not also discard embryos to avoid passing disease between generations? States the director of one IVF clinic, "The possibility of eliminating a fair number of genetic diseases by the end of the decade is exciting."

As IVF becomes more streamlined with extraction of eggs in the clinician's office, freezing of spare embryos, and improved implantation rates, screening of embryos presents an advantageous alternative to carrier or prenatal screening if the goal is eliminating lethal diseases. Arguably it is morally more acceptable to discard embryos than to abort pregnancies. Moreover, it allows a deleterious recessive gene to be eliminated from a family's genetic line. A second option is to use a donated embryo, but if IVF and embryo diagnosis are available, couples would probably prefer their own biological embryo.

Clinicians' more ambitious goal is to prevent disease by correcting genetic defects in embryos. Preimplantation diagnosis will prevent disease passively by discarding embryos with deleterious genes. Embryo therapy will prevent disease in a different way by treating genetic anomalies in embryos and then saving and transferring the embryos. …