Posted By Liam Harris
Earlier this year, a team of doctors successfully carried out a new fertility technique that resulted in the birth of a child containing the genetic information of three people: the mother, the father, and a female donor. The technique allowed the intended parents to have a healthy baby after all of their previous children had died of Leigh syndrome, a debilitating neurological disease.
However, the mitochondrial replacement technique (MRT) remains highly controversial, both medically, due to unknown side-effects, and ethically, because the donor’s genetic information will be passed on to future generations. In fact, American doctors performed this procedure in Mexico to bypass an American ban. MRT is illegal in Canada under the Assisted Human Reproduction Act (AHRA), but other jurisdictions such as the UK have legalized the technique.
What are the risks and benefits of MRT? And what can these developments tell us about our reproductive legal regime in Canada?
The vast majority of human genetic information is carried in the cell’s nucleus. However, there is also DNA contained in sub-cellular structures called mitochondria. Unlike nuclear DNA (nDNA), mitochondrial DNA (mtDNA) is inherited exclusively from the mother. While mtDNA accounts for a very small portion of the genome (about 1%), mutations in these genes can cause serious disease due to the mitochondria’s critical role in cellular energy generation and signalling.
Leigh syndrome is one of these diseases. Patients with Leigh syndrome experience a progressive loss of movement and neurological function. This decline often begins in early childhood, resulting from the inability of their neurons to metabolize energy effectively. These patients will rarely live more than a few years.
MRT aims to prevent Leigh syndrome in the children of mothers carrying mutant mtDNA genes. The mother’s egg is harvested and the nucleus, which contains the vast majority of genetic information she would pass to her child, is removed. The rest of the egg, including the disease-causing mitochondria, is discarded. The nucleus from the mother is then inserted into a donor’s egg. This hybrid egg, containing the mother’s nDNA and the donor’s mtDNA, is then fertilized by the father’s sperm, resulting in an embryo that is implanted in the mother through in-vitro fertilization (IVF). The result is a child whose nDNA comes from both parents, but with a mitochondrial genome inherited from a third party. This genetic material will, in turn, be passed on to future generations if that child is female and has biological children of her own.
Opposition to MRT is based on two main arguments, one medical and one ethical. First, because the technique is new, its side effects are heretofore unknown. Some suggest that it could result in higher rates of cancer or early aging. While experts have no evidence showing the technique to be unsafe, uncertainty persists.
The result is a child whose nDNA comes from both parents, but with a mitochondrial genome inherited from a third party. This genetic material will, in turn, be passed on to future generations if that child is female and has biological children of her own.
Second, critics decry the alteration of the genome in a way that can affect future generations. Slippery slope arguments suggest that this is the first step down a road to “designer babies”, where parents modify the genome of their offspring to meet their every whim. In the case of MRT, it is important to remember that mtDNA accounts for only a tiny portion of the genome and that these genes control basic cellular functioning rather than the types of defining traits often pictured in the case of designer babies. This concern may therefore prove less relevant to this particular genetic change. However, caution is warranted whenever a heritable alteration occurs, because this permanently changes the composition of the gene pool, recognized as the common heritage of humanity.
The replacement of the egg’s mtDNA with that of the donor alters the genome in a way that is potentially inheritable, placing the technique within the ambit of prohibited practices in Canada. Section 5(1)(f) of the AHRA states that “[n]o person shall knowingly alter the genome of a cell of a human being or in vitro embryo such that the alteration is capable of being transmitted to descendants”. Doctors carrying out the procedure in Canada could face harsh penalties: up to $500,000 and a ten-year prison term.
The outright criminalization of heritable genetic alterations seems less and less tenable as new techniques are developed that offer significant medical benefits and manageable risks. In addition to MRT, recent advances in human gene editing have fuelled hopes that inheritable genetic diseases could be eradicated forever, but these procedures would be prohibited under the AHRA for inducing inheritable genetic alterations.
Doctors combine the mother’s nucleus, the donor’s egg, and the father’s sperm to produce a viable embryo for the mother to carry to term. || (Source: Science News)
Meanwhile, the promise of these techniques has begun to attract legislative and regulatory attention worldwide. Last year, the UK Parliament carved out a specific exemption from its prohibition to allow MRT. This legislation addresses a number of practical matters, including the right of the child to request medical information about the donor, and it clarifies that the child is not related to the donor despite the contribution of genetic information. Earlier this year, a report commissioned by the FDA recommended allowing clinical trials of MRT in the United States.
This technique and others like it certainly merit close regulatory attention due to the implications they have for our collective genetic heritage and the uncertainty regarding their side-effects. However, it is impossible to ignore the treatment potential of these techniques in the case of diseases like Leigh syndrome. These developments shine a negative light on the restrictive reproductive landscape in Canada. The embattled AHRA provides neither the flexibility nor the clarity needed to confront these new regulatory challenges. Patients, medical professionals, and the public deserve clear rules that properly manage the risks while securing the benefits associated with this promising new medical frontier.