The genome: you gain some, you lose some": Martyn H Breuning (1) thinks about the theory behind the science. Here, he writes:
A key proposition of Darwinian theory is that animal species need to be able to modify their properties by mutating their DNA to adapt to environmental change and to evolve. Thus a certain rate of spontaneous mutation is not only a reflection of the fallibility of the DNA replicating machinery, but also a prerequisite for survival of the species, and the origination of new life forms. Since the vast majority of arising mutations are either neutral or detrimental, and only a minute proportion is beneficial, this adaptability to the environment comes at a very high price in terms of disease....
The results obtained by Turner et al clearly confirm the suspicion that our germ cells always contain a subset of unbalanced products from meiosis. Those deletions and duplications that cause such major defects to be embryonically lethal, may cause early spontaneous abortion, or even inability to fertilize. In man, such defects have yet to be identified. Those that can cause congenital malformations and/or mental retardation are increasingly recognized by clinicians and by high resolution molecular karyotyping. Those deletions and duplications that have little or no effect on the phenotype will largely pass unnoticed....
The variable phenotype often complicates the distinction between pathogenic rearrangements and neutral variants. A complete characterization of the effects of copy number variants is not only necessary for diagnosis and genetic counseling, it will also improve our understanding of the diseases involved.
(1) http://www.nature.com/ejhg/journal/v16/n6/full/ejhg200854a.html
from the European Journal of Human Genetics (2008) 16, 663; doi:10.1038/ejhg.2008.54; published online March 12, 2008
M. Breuning, Department of Clinical Genetics, Center for Human and Clinical Genetics, Leiden University Medical Center, The Netherlands