Characteristics of Cloned Animals and Related Ethical Consequences

If all goes well, a genetic copy of the animal being cloned is produced, but, again, one clone can vary considerably in phenotype from the donor for numerous traits. Unfortunately, natural reproduction does not go well in every case, and such problems are greatly exacerbated with cloning. In a 2002 summary of all available information on animals cloned from somatic cells (38 studies resulting in 335

subjects in 5 species), Jose B. Cibelli and colleagues found that 77 percent of the resulting animals were normal, while 23 percent were not. The normal subjects, though mostly adults, had not yet lived out their normal life spans, so additional problems (over and above those due to normal aging) could yet develop. Cloning from somatic cells has not resulted in monsters, but, in most cases, reasonably normal individuals.

However, 23 percent abnormalities, mostly neonatal death, is completely unacceptable ethically for producing children, and for most scientists working in this area that ends the ethical debate on human reproductive cloning. In the Cibelli survey it was noted that many of the animals produced represented the initial, or at least early, studies on cloning in respective laboratories, and that the incidence of abnormalities likely would decrease with more experience and improved techniques. This is already being borne out in the scientific literature, but it likely will be many years before the incidence of problems with somatic-cell cloning will decrease to acceptable levels for reproductive cloning of people. However, this ethical crutch will also likely disappear with time.

A complex ethical question is where to set the boundaries on acceptable levels of abnormalities. Interestingly, a 2002 study by Michèle Hansen and colleagues that looked at children produced via in vitro fertilization showed that congenital abnormalities were approximately double the 4 percent seen with natural reproduction. Most of these abnormalities were not extremely serious and could be circumvented or repaired. Nevertheless, the abnormalities were doubled, and some were serious. Thus, this ethical problem is already with us.

The question boils down to the right of people to reproduce given an increased risk of an abnormal child. Of course, these questions arise outside of the context of assisted reproductive technology, such as the increased risk of a child with Down's syndrome when older women reproduce. Modern science can minimize such suffering (e.g., by genotyping embryos before transfer back to the uterus, and eliminating those that will result in severely abnormal individuals). Another reality is that, in one sense or another, nearly all persons are abnormal. For example, essentially all humans have lethal or severely debilitating recessive alleles in their genetic makeup, which, if matched with another such allele in a gamete of a mate, will result in death of the conceptus or resulting child.

A frequent abnormality that occurs with cloning by nuclear transfer via embryonic or somatic donor cells is fetal overgrowth. It is not unusual for offspring to be 30 or 40 percent larger than normal at birth. In some studies, up to 30

percent of offspring have this condition, known as large-offspring syndrome, and some animals cloned from the same donor are large, some are normal, and some are small— which elegantly illustrates that identical chromosomal identity does not equal identical phenotype. Large-offspring syndrome is not a genetic trait, in that this problem is not transmitted to the next generation when the cloned animals reproduce naturally. Also, Michael Wilson and colleagues showed in 1995 that these excessively large neonates develop into only slightly larger adults. The scientific consensus is that large-offpsring syndrome can be summarized as a genetically normal fetus in an epigenetically abnormal placenta. That is, the placenta from cloned pregnancies is often abnormal, resulting in secondary problems in the fetus that largely correct themselves after birth. Unfortunately, with routine husbandry, the newborns often die because of being debilitated from gestating in an abnormal placenta. Fortunately, with a few days of intensive care starting at birth, such offspring survive reasonably well and develop normally, as shown by Frank B. Garry and colleagues in 1995.

As with human babies, animal offspring derived from in vitro fertilization or long-term in vitro culture of embryos have a much higher incidence of abnormalities than with normal reproduction, but a lower incidence than with cloning (see Kelley Tamashiro and colleagues). Clearly, some (but not all) in vitro manipulations, particularly when the in vitro period exceeds several days, lead to increased problems in resulting offspring. Thus, there is a baseline of problems with natural reproduction, which increases with the amount of in vitro manipulation (and reaches a higher level with somatic-cell cloning). It is likely that these problems will decrease or be circumvented with improved techniques, and also that the basic information obtained will be useful in decreasing birth defects and neonatal problems that occur with natural reproduction.

There are some special problems with a small percentage of pregnancies from somatic-cell cloning that are not just an increase in incidence of naturally occurring problems. In some cases, the immune system appears to be severely compromised, and there can be major problems with the heart, blood vessels, and kidneys that are extremely rare with normal reproduction. Furthermore, there is an unusual amount of embryonic death and fetal absorption or abortion with cloned pregnancies—over 80 percent embryonic and fetal attrition is not unusual (compared with around 30 percent with normal reproduction). Thus, the incidence of problem conceptuses is very high, and most of these die in early pregnancy. This is still another reason that, as practiced at the beginning of the twenty-first century, reproductive cloning should not be done with human embryos.

A final point is that cloning via nuclei from somatic cells is very inefficient, currently on the order of 2 percent success per oocyte. This is due to the multiplicative attrition (or success) of the various steps. For example, if there is 90 percent successful fusion of donor cell and oocyte, with 50 percent dividing into embryos suitable for transfer to recipients, 30 percent embryonic survival until pregnancy can be diagnosed, 20 percent of diagnosed pregnancies developing to term, and 85 percent surviving the neonatal period, the result is an overall success rate of around 2 percent. These are typical current values, and are one reason why the costs of cloning are so high. While success rates are improving, it will likely be some years until overall success even approaches 10 percent. For human reproductive cloning, dozens of women would need to be involved as donors of oocytes and recipients of embryos to produce even one baby—assuming the procedures worked as well as they do with animal models, which is unlikely. This illustrates another ethical issue, in that undue use of scarce and expensive medical resources would be required for clonal human reproduction.

Kicking Fear And Anxiety To The Curb

Kicking Fear And Anxiety To The Curb

Kicking Fear And Anxiety To The Curb Can Have Amazing Benefits For Your Life And Success. Learn About Calming Down And Gain Power By Learning Ways To Become Peaceful And Create Amazing Results.

Get My Free Ebook


Post a comment