Human genome research project discusses latest findings at medical law conference 2008

Current parameters for pre-implantation genetic diagnosis (PGD) extend further than was initially intended by the makers of current policy, say the latest findings of the University of Otago-based Human Genome Research Project.

The New Zealand Law Foundation-sponsored group has been examining the existing legal boundaries of PGD and looking at how the current legal framework needs to be changed to keep pace with new and emerging applications of PGD.

Project leader and Law Faculty Dean Professor Mark Henaghan says the first section of the project's latest findings looks at the legal, ethical and policy implications of the use of PGD to test for single-gene mutations that could leave people susceptible to developing a particular disease later in life, for example, hereditary breast or bowel cancer that run in the family. Susceptibility testing of embryos for such mutations before implantation gives a mere indication of an increased or decreased risk of a disorder developing.

"PGD to diagnose such mutations is a contentious practice. It differs – whether by design or by good fortune – from the original objective initially intended by makers of current policy on PGD, which was to diagnose the most serious, life-threatening genetic conditions that appear at birth or in the first few years of life. The makers of the original policy created a wide threshold test for the use of PGD, enabling its use in situations where there may be future serious impairment. This approach allows New Zealand to keep pace with the rest of the common law countries in evolving uses of PGD such as in cases where families may be susceptible to hereditary breast or bowel cancer."

The second section of the HGRP's research report examines the use of PGD to perform preimplantation exclusion testing for embryos which may, or may not, be at risk of inheriting the autosomal dominant disorder Huntington's disease. The HGRP analyses whether preimplantation exclusion testing is permitted under current regulation, and whether or not it ought to be.

"This procedure is distinct from other applications of PGD which are performed to diagnose a particular genetic condition in an embryo," says Professor Henaghan.

"Preimplantation exclusion testing is performed when the at-risk prospective parents do not want to undergo predictive testing to determine whether they have the gene mutation for Huntington's disease. Nor do they wish to diagnose the presence of the mutation in the embryo – because it could indicate their own genetic status."

Rather than testing embryos to determine if they have inherited the gene for Huntington's disease, they are tested to see if the relevant section of chromosomal DNA, which encodes for Huntington's disease, originated from the affected would-be grandparent.

Embryos found to have inherited that section of DNA are excluded as high risk and not suitable for implantation.

"Exclusion testing is contentious because half of the couples who undertake it will not be at-risk, something which could be determined by the parents themselves undertaking predictive testing," says Professor Henaghan.

"In addition, of those couples that are at-risk, half of the embryos discarded will be unaffected."

The HGRP's findings conclude that preimplantation exclusion testing is permissible under the Human Assisted Reproductive Technology (HART) Order of 2005 as an established procedure. This is because of the sufficiently wide threshold for the use of PGD in situations where there may be future serious impairment, without the need for ethical oversight.

The Human Genome Research Project has released two major reports prior to these findings. The first examined and questioned the ethical, legal and regulatory issues surrounding the use of PGD, as well as address Mâori cultural perspectives. The second tackled the genetic testing of embryos, newborns, children and communities, and examined new testing technologies and their implications.

The latest findings were presented at the 9th Annual Medical Law Conference held in Wellington.

(Source: University of Ontago: April 2008)