The concept of designer babies has been a subject of speculation in science fiction as well as a popular theme in ethical debates for decades. While most debates on the science behind genetic babies focus on should-or-shouldn’t issues, several technological barriers have already been overcome, allowing more and more people to instead focus on questions of how and when designer babies will come into actuality. The truth is, to some extent, they already exist.
One instance through which the goal of a designer baby has already been partly realized is sex selection, the technology for which has been around since the turn of the century. Genetic sex selection is done through a relatively simple process of sperm sorting, as it is the sperm that contributes either an X or a Y chromosome to a baby’s DNA, therefore making it the sex-determining gamete.
Y chromosomes contain slightly less DNA than X chromosomes – a fact which enables scientists to successfully distinguish sperm cells that tend to produce boys from those that tend to produce girls by staining the sperm’s DNA with a light-sensitive dye. This sex selection method is known as MicroSort. The chosen sperm is then either deposited directly into the uterus or used in the in vitro fertilization of eggs before implantation. In 2001, the Genetics and IVF Institute in Fairfax, Virginia reported a 90% success rate for girls and 73% for boys from Microsort gender selection.
Sex selection, a milestone in the science behind genetic babies, has proven to be particularly helpful to couples with a family history of X-linked diseases. Examples of these disorders, which almost always affect males, include hydrocephalus, hemophilia, Duchenne muscular dystrophy, and Fragile X syndrome.
Pre-Implantation Genetic Diagnosis (PGD)
PGD, another turn-of-the-century technology, is used to test embryos formed in vitro for genetic conditions prior to implantation in the uterus. PGD increases the chances of a successful pregnancy and reduces the risk of gene-related diseases in offspring. Of course, this technology produces designer babies only in the sense that their parents have the power of selection; however, 100% of the babies’ genes are still naturally inherited from the parents.
Two main methods are used in prescreening: polymerase chain reaction (PCR), which helps pinpoint monogenic disorders, and fluorescent in situ hybridization (FISH), which detects chromosomal abnormalities. One or two undifferentiated cells are commonly removed from the eight-cell embryos for testing. No genetic modification of the embryo is involved.
Today, PGD is used for strictly therapeutic purposes only; that is, it is only used to ensure that the babies produced do not have a genetic predisposition for disease. In 2009, a fertility clinic in Los Angeles offered PGD as a means of letting parents choose their babies’ hair and eye color. The program was soon shut down due to public outrage.
The science behind genetic babies doesn't end there; other methods have been proposed which may someday, in theory, give rise to truly custom-designed babies. Human Germline Genetic Modification (HGGM) is one such method, wherein a change in the genetic makeup of the egg, sperm, or early human embryo would cause the baby to manifest certain genetic traits he can in turn pass on to his descendants. Another proposed method is Somatic Cell Nuclear Transfer (SCNT), which involves complete genome replacement and is therefore considered a form of cloning.