Comprehensive Chromosome Screening (CCS): a promising procedure
involves the analysis of the total chromosome complement of a single cell or
group of cells from each embryo. These tests that look into the essence of
humanity, allowing scientist and physicians the opportunity and ability to
alter the human genotype for better or worse. The common thread of life is DNA
and DNA is the only major requirement for genetic screening. With knowledge of
structure and function of DNA scientists can unlock the mysteries of life.
Screening tests can be performed in order to collect a variety of
information, including the risk of a chromosomal abnormality. Most of these
tests are relatively non-invasive and do not carry a high amount of risk.
Sometimes though, these tests are not conclusive. Depending upon your age and
medical history, your health care provider may recommend one or more of the
What is DNA?
is the molecule of heredity. DNA provides life its blueprints for building,
replicating and surviving. Humans have a wide variety of DNA sequences, but the
majority of sequences are common to all humans. DNA condenses to form
chromosomes. Humans have forty-six chromosomes that form twenty-three pairs;
each chromosome is made up of thousands of genes. Gene interaction controls the
physical and structural characteristics of organisms. Allelic pairs make up
genes. Interactions between different types of alleles create different
genotypes, which is expressed by different phenotypes. The information gained by
the sequencing of the human chromosome can be compared and contrasted with the
DNA sequences of individual that posses a certain trait. This will also help in
avoiding fetal abnormality and conception for
patients. This will allow scientist to determine which gene or sets of genes
control a trait. After a trait is defined and the most likely sequence mapped, a
genetic test can be developed to compare the sequences of an individual and
determine if the individual is predetermined to develop a disease or trait. By
using comparative analysis techniques, genetic screening plays the role of an
indicator. The results allow insight into whether the individual shows trends
towards risk of contracting a
disease. The process doesn't necessarily determine whether or not an
individual will have a trait rather it will show the genetic makeup that is most
likely responsible for that trait.
Types of Chromosome Screening
Carrier Identification includes genetic tests used by couples whose
families have a history of recessive genetic disorders and who are considering
having children. Three common tests include those for cystic fibrosis, Tay-Sachs
disease, and sickle-cell trait.
Diagnosis is genetic testing of a
fetus. This may occur when
there is a risk of bearing a child with genes associated with mental retardation
or physical deterioration. Down Syndrome is one of the most common genetic
diseases screened by this method.
Newborn Screening is frequently done as a preventative health measure.
Tests usually have clear benefit to the newborn because treatment is available.
Phenylketonuria and congenital hypothyroidism are conditions for which testing
is conducted in all 52 states.
Late-onset Disorders include adult diseases such as
heart disease. These diseases are complex and have both genetic and
environmental causes. Genetic tests may indicate a susceptibility or
predisposition for these diseases. There are diseases caused by single genes,
such as Huntington's disease, that also are seen later in life and can be tested
at any time.
Identification of genetic information belonging to a specific
individual has received a great deal of press coverage lately. Profiles (aka
"DNA fingerprints") are complied from the results of DNA testing for one or more
genetic markers to identify unique characteristics of an individual. This
information is currently used in legal cases involving paternity and in criminal
investigations, and it can be used in time of major accidents, disasters, or
wars to identify those who have died.
Potential CCS Advantages
Test results can provide a sense of relief from uncertainty and help people make
informed decisions about managing their health care. For example, a negative
result can eliminate the need for unnecessary checkups and screening tests in
some cases. A positive result can direct a person toward available prevention,
monitoring, and treatment options. Some test results can also help people make
decisions about having children. Newborn screening can identify genetic
disorders early in life so treatment can be started as early as possible.
The more traditional technique of performing PGS employed fluorescent in
situ hybridization (FISH). FISH analysis on a single cell is limited to
analysis of 5-10 chromosome pairs out of the 23 pairs of chromosomes.
Since aneuploidy (chromosomal abnormalities) can affect any chromosome, it would
be beneficial to expand PGS to include screening of all 23 pairs of
chromosomes. In fact, several research studies have shown that
performing PGS with FISH techniques on the day 3 embryo does not improve
outcomes. Analysis of the entire chromosome complement of the embryo or oocyte,
combined with further improvements in technology, could potentially further
increase the likelihood of implantation and decrease the chance of miscarriage
for patients and potentially decrease the number of embryos necessary for
Performing a biopsy on the blastocyst stage embryo also allows us to obtain
several cells, as opposed to current practice, which allows removal of only a
single cell from the less advanced day 3 cleavage stage embryos.
Comprehensive Chromosome Screening (CCS) could be a promising and beneficial
PGS procedure for patients seeking to increase their chances of implantation and
a live birth.
For more information, you can consult WF fertility expert, Dr Vaishali
Tandon. She is a specialist covering areas targeting In Vitro Fertilization
techniques, like, IVF, ICSI, Laser assisted embryo matching, pre-implantation
genetic diagnosis, embryo freezing, sperm freezing, oocyte freezing.
Amniocentesis, FISH and Karyotyping are also her areas of focus to help women
seek pregnancy (50-60 % is the successful pregnancy rate at present).