Page 10 - 2021 Winter CMTA Report

Advances in Genetics:

New Tools for Prospective Families

BY CHRISTINE MURRAY, MD

dvances in genetic tech- disorder. Huntington’s disease are more common among certain
nology have allowed for and Marfan syndrome are exam- populations. Comprehensive car-
the development of ples of autosomal dominant rier screening panels now test
powerful tools to assist inheritance. X and Y chromo- for nearly 300 single-gene
A people as they begin to somes can also carry genetic defects. The American College of
plan their families. Multiple mutations: Hemophilia and frag- Obstetrics and Gynecology rec-
techniques are available to pro- ile X syndrome have an X-linked ommends that women have
vide prospective parents with inheritance pattern. genetic carrier screening as part
valuable information to plan and The Human Genome Project, of their routine prenatal evalua-
prepare. This overview, while not a multinational scientific collab- tion. Reproductive options for
comprehensive, offers a look into oration completed in 2003, is at-risk couples include IVF with
what modern genetic analysis widely considered one of the preimplantation genetic testing
can do. most ambitious scientific under- (PGT), conception with donor
A review of basic genetics takings of all time. The finished eggs or sperm or adoption.
provides a good starting point. project sequenced 3 billion DNA
Human beings have cells con- letters covering 99 percent of the NON-INVASIVE PRENATAL
taining 46 chromosomes: Two human gene-containing regions. TESTING/SCREENING
will code for gender at birth (X It is hard to overstate the NiPT is a genetic test that is per-
and Y). The remaining 22 auto- tremendous impact of this under- formed once pregnancy has been
some pairs consist of maternal taking. The results have been established. It requires a simple
and paternal DNA. These paired used to identify a genetic source blood draw and can be done as
chromosomes contain hundreds for a multitude of medical issues, early as nine to 10 weeks of preg-
of thousands of DNA strands— including cancers, as arising from nancy. The test analyzes tiny
genes that code for all the traits specific mutations. Understand- fragments of cell-free DNA from
that make us who we are. ing the genetic basis of disease the developing placenta to assess
Defects in any of these genes can opens the door for specific diag- the genetic health of the devel-
lead to specific disorders. Such nostic tools and treatments. oping baby.
single-gene mutations can be Unlike carrier screening,
inherited in an autosomal reces- GENETIC CARRIER which provides information
sive manner, which means that SCREENING about specific genes, NiPT is
an affected child received one Carrier screening refers to a used to detect chromosomal dis-
defective gene from each parent. blood test that can identify silent orders that are caused by the
The parents, each having gene mutations. Prospective par- presence of an extra or missing
only one affected gene, are con- ents are now routinely offered copy (aneuploidy) of a chromo-
sidered silent carriers and are this screening to identify some of some. NiPT primarily looks for
not affected by the disorder. the most common mutations like trisomy 21 (Down syndrome),
Their offspring has a 25 percent the genes for cystic fibrosis (CF), caused by an extra chromosome
chance of having the disorder spinal muscular atrophy and at position 21, trisomy 13 and 18
and a 50 percent chance of being fragile X syndrome. This basic and extra or missing copies of
a silent carrier. carrier panel is offered to one the X and Y chromosome. NiPT
Examples of autosomal potential parent. If a silent can also identify gender. NiPT is
recessive disorders are cystic mutation is identified, the other a screening test, which means
fibrosis, sickle cell anemia and parent is tested. There are that it cannot give a definitive
spinal muscular atrophy. Some expanded panels recommended answer about whether the preg-
disorders are autosomal domi- for parents based on their ethnic nancy is affected. The test can
nant—inheriting only one backgrounds. Tay Sachs, sickle only estimate whether the risk of
abnormal gene will lead to the cell anemia and the thalassemias having certain conditions is

10 THE CMTA REPORT WINTER 2021