for medical students

1. GENETICS AND GENETIC
DISORDER
DR SWATI SINGH
CONSULTANT OBSTETRICS AND GYNECOLOGY
MCH BISHA

2. LEARNING OBJECTIVES
• BASIC CONCEPT
• RISK FACTOR FOR GENETIC DISORDER
• GENETIC DISORDER SCREENING
• GENETICS IN GYN
• EVALUATION OF PATIENT WITH SUSPECTED GENETIC
DISORDER
• COUNCELLING

3. BASIC CONCEPT OF GENETICS
• Gene – basic unit of genetic information. Genes
determine the inherited characters.
• Genome – the collection of genetic information.
• Chromosomes – storage units of genes.
• DNA - is a nucleic acid that contains the
genetic instructions specifying the biological
development of all cellular forms of life

4. HUMAN GENOME
Most human cells
contain 46 chromosomes:
• 2 sex chromosomes (X,Y):
XY – in males.
XX – in females.
• 22 pairs of chromosomes named
autosomes.

7. Genotypes Phenotypes
• At each locus (except for sex chromosomes) there are 2
genes. These constitute the individual’s genotype at the
locus.
• The expression of a genotype is termed a phenotype. For
example, hair color, weight, or the presence or absence of
a disease.

8. DOMINANT VS. RECESSIVE
• A dominant allele is expressed
even if it is paired with a recessive
allele.
• A recessive allele is only visible
when paired with another recessive
allele.

9. MEDICAL GENETICS
When studying rare disorders, 6 general patterns of
inheritance are observed:
• Autosomal recessive
• Autosomal dominant
• X-linked recessive
• X-linked dominant
• Codominant
• Mitochondrial

12. GENETIC
DISORDERS
OF THE
FETUS
• Genetic disorders occur when a problem in the
baby’s chromosomes or genes causes physical
abnormalities or illnesses.
• In our body, we have millions of cells. In each
cell, there are 46 chromosomes, found in 23
matching pairs.
• Half of the chromosomes are passed on from a
person’s mother, and half from their father.
• These chromosomes carry our DNA, or genes,
which are the instructions for how we look and
how our body develops and functions.

13. GENETIC
DISORDERS
OF THE
FETUS
• When a harmful change occurs in these
instructions, it can change the way a baby
develops.
• Babies with genetic disorders can be at risk
of slow mental and physical development,
physical abnormalities, and lifelong
illnesses.
• Some genetic disorders are hereditary,
meaning the genetic change is passed on
from their parents.
• Other genetic changes can happen for the

14. RISK
FACTORS
FOR GENETIC
DISORDERS
•Family history of a genetic disorder
•Prior child with a genetic disorder
•One parent has a chromosomal
abnormality
•Advanced maternal age (35 or older)
•Advanced paternal age (40 or older)
•Multiple miscarriages or prior stillbirth

15. TYPES OF
DISORDERS
SINGLE GENE DISORDER
CHROMOSOMAL
ABNORMALITY
MULTIFACTIRIAL OR
COMPLEX
ABNORMALITY
TERATOGENIC
• Single gene disorders occur when a
change in one gene causes a disease.
Examples include cystic fibrosis, sickle cell
anemia, Tay-Sachs disease, hemophilia,
and Marfan syndrome.
• Chromosomal abnormalities occur where
there are missing or extra chromosomes,
or pieces of chromosomes. Down
syndrome, the most common
chromosomal abnormality, is caused by an
extra chromosome number 21.
Chromosome abnormalities can be

16. TYPES OF
DISORDERS
• Multifactorial or complex disorders are caused
by a combination of genetic predispositions and
environmental factors, which makes it harder to
predict who may be at risk. Examples include
heart defects, cleft lip or cleft palate, and spina
bifida.
• Teratogenic disorders occur when the baby is
exposed to substances during pregnancy that
cause abnormalities, otherwise known as
“teratogens.” Babies are very sensitive in the first
trimester, when all of the organs are developing.
Teratogens include alcohol, drugs, lead, high
levels of radiation exposure, and certain
medications, infections and toxic substances.

17. TESTING FOR GENETIC DISORDERS
THERE ARE TWO TYPES OF TESTING FOR GENETIC DISORDERS:
Screening tests – these tests check the risk of your
baby having certain genetic disorders
Diagnostic tests – these tests can detect if certain
genetic disorders are present in the baby

18. SCREENING
TESTS
• Carrier screening is a blood test that tries
to determine if either parent carries a
genetic change for inherited disorders that
could be passed on to the baby.
• It can also be performed on a saliva
sample. The best time to do this screen is
before getting pregnant, but it can be
done during pregnancy as well. While this
screen can check for many conditions at
once, it is not currently possible to screen
for every disorder that could be inherited.

19. SCREENING
TESTS
• Prenatal genetic screens are a series of first and
second trimester screens that use blood samples
from the mother as well as ultrasounds to check
the baby’s risk of having certain common genetic
disorders. Examples include Down syndrome and
certain birth defects, such as spina bifida.
• Noninvasive Prenatal Testing (NIPT) or cell-
free DNA screening is a blood test that checks
DNA from the placenta that is found in the
mother’s blood. This screens for the most
common chromosome abnormalities, such as
Down syndrome and trisomy 18, and is most
commonly used in high-risk pregnancies.

20. DIAGNOSTIC
TESTS
• Diagnostic tests are performed during
pregnancy to detect if certain genetic
disorders are present in the baby, such as
cystic fibrosis or Down syndrome. Some
diagnostic tests can also check for neural
tube defects, like spina bifida.
• Diagnostic tests are generally safe
procedures when performed by an
experienced physician
• However, all procedures carry a small risk
of a complication which can include an

21. ROUTINE
DIAGNOSTIC
TESTS
INCLUDE:
• Chorionic villus sampling tests a sample
of tissue taken from the placenta in the
first trimester
• Amniocentesis: Tests a sample of the
amniotic fluid taken from the womb in the
second trimester

22. ADVANCED
DIAGNOSTIC
TESTS
• Fetal blood sampling or percutaneous
umbilical blood sampling (PUBS)
• Prenatal Chromosome Analysis
(Karyotype)
• Prenatal Chromosomal Microarray
Analysis (CMA)
• Fetal genomic or whole-exome
sequencing (WES)

24. GENETIC COUNSELING
• Assess the risk of having a baby with a genetic disorder
• Review your testing options
• Coordinate genetic screenings and diagnostic tests and interpret
the results
• Provide emotional support and educational resources for the
patient & family
• Help you make informed decisions about your pregnancy and your
baby’s treatment, and prepare for appropriate medical care

25. TREATMENT FOR FETAL GENETIC DISORDERS
• Treatment depends on the genetic disorder and the individual pregnancy.
• Specialized care from a maternal-fetal medicine physician
• Individualized care based on the genetic disorder
• Treatment options ranging from medical therapy during pregnancy, such as
fetal interventions, to surgery immediately after birth
• A multidisciplinary, collaborative healthcare team, including genetic counselors,
imaging specialists, fetal specialists, fetal and neonatal surgeons and
neonatologists and pediatricians experienced in the treatment of children with
genetic disorders

26. GENETICS IN GYNAECOLOGY AND CANCER
SCREENIG
• SOME BREAST AND OVARIAN CANCER HAVE
GENETIC PREDISPOSITION
• BRCA1 AND BRCA 2 GENE
• LYNCH 1 SYNDROME OR HEREDITORY
NONPOLYPOSIS COLORECTAL CANCER TYPE A

27. GOALS OF GENETIC TESTING
• Understand cause of cancer in family
• Surveillance and prevention of other cancers
• Allow unaffected family members to test
• Surveillance
• Prevention options
• Family planning