A team at Brigham and Women's Hospital in Boston believe that the drug will provide an alternative to the current pill, which can cause side-effects such as mood swings, blood clots and a slightly increased risk of breast cancer.

The scientists say the drug will be administered by way of a patch which will block a gene that produces a protein called ZP3, which allows the sperm to bind to the outer layer of a woman's egg.

Once the protein is blocked it would make it impossible for the sperm to enter the egg and fertilise it.

The therapy is based on a process called RNA interference, where specific genes are turned off, but to date it has only been tested in mice and human kidney cells.

Researcher Dr. Zev Williams says human trials of the pill are a decade away but an alternative to hormonal contraceptives is long due.

Dr. Williams says there is no contraceptive drug that is non- hormonal and reversible so he is trying to think about contraception in a new way which will require a great deal of time and effort.

Dr. Williams presented the findings at the American Society for Reproductive Medicine conference in Washington DC.

Considering the high heritabilities for global brain volumes and particular focal brain densities and thicknesses, the search for genes that are involved in brain growth, aging, and brain structure maintenance is important. Such knowledge can help us understand normal developmental and age-associated changes in individual variation in brain functioning. Moreover, it enhances our knowledge of individual variation in brain functioning and facilitates the interpretation of the morphological changes found in psychiatric disorders such as schizophrenia [van Haren et al., 2007]. Also, it allows future efforts to find particular genes responsible for brain structures to be concentrated in areas that are under considerable genetic influence [Hulshoff Pol et al., 2006].

A genetic approach to find genes involved in brain structure that has been applied in several studies is that of diseases with a clear genetic etiology such as Huntington's disease, Down syndrome, Williams syndrome, and Velocardiofacial syndrome. A review reveals for these diseases besides disease specific brain changes, decreases in total brain, white matter, and hippocampus volumes, irrespective of the genes and/or chromosomes involved. This suggests that many genes are probably involved in the individual variation of these measures [Peper et al., in press].

It is important to investigate which environmental factors have an influence on the expression of genes (as found in DNA-methylation). Additionally, the study of interaction between genes and environmental factors is warranted. Furthermore, the simultaneous effects of multiple genes and possibly the interaction among genes, also needs investigation as the high heritability of a complex quantitative phenotype such as brain volume cannot be explained by a single-gene polymorphism

Conclusion

MRI studies in twins indicate that, given the basic additive genetic model, overall brain volume in adulthood is highly heritable. To test for influences of genetic, common, and unique environmental factors or interactions between genetic and environmental influences. twin studies carried out in large and more homogenous samples, analyzed with advanced quantitative genetic methods are needed. To investigate the stability of genetic and environmental influences onto functional neural networks in human brain longitudinal twin studies in childhood as well as in adulthood are needed since brain volume changes dynamically throughout life. New brain-imaging methods, such as DTI-fiber tracking and resting state functional MRI, allow to study the heritability of neural networks underlying brain functioning. These new methods, in coherence with new genetic approaches, will enable us to further disentangle which genes and environmental factors and interactions therein influence human brain structure throughout life.

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