Biomedical Engineering Reference
In-Depth Information
correlate CNVs with risks for developing different diseases. These studies
have already shown that CNVs are a relatively common occurrence in the
development of many cancers. Several reports also show that one can use
these techniques to expand upon standard cytogenetic analysis and data-
bases are being developed to attempt to correlate CNVs with different
genetic syndromes. As these methodologies become more advanced and
more affordable it is likely that CNV analysis will become a standard part
of routine analysis for genetic diseases.
CNVs are also important in our understanding of some infectious dis-
eases. For example, studies have shown that the eventual development of
HIV infection may be related to the number of copies one has of the natu-
rally occurring gene (CCL3L1) whose protein product binds and blocks the
HIV viral cell receptor (CCR5). Population studies show that individuals
with higher copy numbers of CCL3L1 seem to be more protected from HIV
infection than those having the fewest copies of this gene.
7.9 Epigenetic effects on the genome
Mutagenesis of the genetic material can take many forms and can result in
dramatically altered phenotypes. Recently a new line of evidence has shown
that there is another level or layer of information that can be placed on a
gene, which is a modifi cation other than one that affects the gene sequence
of the chromosome, but does have an effect on the expression of the gene.
This layer of modifi cations is called an
epigenetic effect
, and the term epig-
enome is often used to include these modifi cations and the phenotypic
changes they can cause. These epigenetic modifi cations can be on chroma-
tin proteins that are intimately associated with the DNA or they can be on
the DNA itself.
Two good examples of the role epigenetic effects can have on gene expres-
sion are:
1 .
chromosome remodeling
that occurs when acetyl groups are added to
histone molecules, altering their confi guration to permit gene expression
or when methyl groups are added to histones, having a silencing effect
on gene transcription; and
2 .
genomic imprinting
, when methyl groups are added to regulatory
sequences of genes and silence them as in some well-known genetic syn-
dromes, or when hypermethylation of one of the two X chromosomes in
normal human females results in silencing the genes on this inactivated
X for gene dosage compensation.
Recent studies have shown that epigenetic changes can be triggered by
environmental factors that range from stress to nutrition, and that these
