genetic screening for diseases and conditions

2. Sanman Samova
Roll no-02
HG SEM-2
School of science.

3.  Genetic testing is a type of medical test
that identifies changes in chromosomes,
genes, or proteins
 The results of a genetic test can confirm
or rule out a suspected genetic condition
or help determine a person’s chance of
developing or passing on a genetic
disorder
General Information

4.  One of the fastest moving fields in
medical science.
 A technique to determine the genotype
or phenotype of an organism.
 It is often used to detect faulty or
abnormal genes in an organism.

5.  To detect disease-related genotypes,
mutations, phenotypes, or karyotypes for
clinical purposes

6.  Constitutional
• Tests for mutations that affect ALL CELLS in
the body, and have been there since
conception
 Acquired
• Tests for changes that affect only certain cells
or cell types in the body, and that occurred
later in life

7.  Molecular Tests
 Cytogenetic Tests
 Biochemical Tests

8. Analysis of DNA
sequence in patient with
a rare inherited disease
Muscular Dystrophy
Gene: DMD
Clinical Picture
1 in 3500 male births
progressive muscle
weakness starting in
early childhood
wheelchair by age 12
death in 20s

9. Molecular Test: Muscular DystrophyMolecular Test: Muscular Dystrophy
 Obtain blood sample from child
 Read the DNA sequence of the DMD
gene
 Identify the mutation that caused the
disease

10. How is this information useful?How is this information useful?
 Can test Mom – Is she an unaffected
carrier of the mutation? Is she at risk to
have more children with this disease?
 Can test siblings of affected child
 Can offer prenatal diagnosis in Mom’s
next pregnancy OR
 Can offer pre-implantation genetic
diagnosis
 Can provide information about prognosis

11. Cytogenetic Test: ExampleCytogenetic Test: Example
 Karyotype – to examine the
chromosomal complement of an
individual including number, form,
and size of the chromosomes.
 Frequently used for children who
present with multiple anomalies,
developmental delay, autism

12. Cytogenetic Test: Child with MCACytogenetic Test: Child with MCA
and autismand autism
 Obtain a
blood sample
from baby
 Look at
chromosomes

13. New type of Cytogenetic TestNew type of Cytogenetic Test
 Cross between a molecular and Cytogenetic test –
arrayCGH- tests for presence/absence of genes at
1000s of positions on each chromosome. Much more
sensitive than a karyotype

14. How is this informationHow is this information
useful?useful?
 Can determine exactly which genes are
involved
 Can test parents and siblings of affected
child to see if they carry the abnormality
 Can offer prenatal diagnosis in next
pregnancy OR
 Can offer pre-implantation genetic
diagnosis
 Can provide information about prognosis

15. Bio-chemical TestBio-chemical Test
 Analyzes the quantity of a downstream
product of a gene (e.g. not looking
directly at the gene, or the
chromosome).
 Example: Newborn Screening
• Mandated in all 50 states
• Twenty primary targets that all states do
• Over 4 million newborns tested each year

16. Biochemical Test: PKUBiochemical Test: PKU
 Phenylketonuria
• Inherited metabolic disorder
• If untreated, leads to mental retardation, seizures
• Affects 1 in 20,000 newborns
Missing enzyme:
Phenylalanine Hydroxylase
Measure amount of
Phenylalanine in baby’s
blood

17.  Can diagnose the baby in time to
treat and avoid all clinical
consequences of the disease
Treatment: Restrict phenylalanine in the diet
 Can test siblings of affected child to
see if they are carriers for the
disease (1 in 70 in the general
population are carriers)

18. Genetic Tests forGenetic Tests for AcquiredAcquired MutationsMutations
 Molecular Tests
 Cytogenetic Tests
Tests for changes that affect only certain cells or cell types in
the body, and that occurred later in life

19. Molecular Test for Acquired DiseaseMolecular Test for Acquired Disease
 KRAS gene test on tumor tissue from
patients with colorectal cancer
• Obtain tumor from patient
• Extract DNA; treat with enzyme that allows
visualization of the mutation

20. How is this informationHow is this information
useful?useful?
 Patients who’s colon tumors do not have
a KRAS mutation are much more likely to
respond to Cetuximab therapy
 Identifies patients most likely to benefit
from specific therapies
 Allows choice of alternative therapies
(and saves time and money) for patients
unlikely to respond

21.  Prenatal screening
 Newborn screening
 Carrier screening

22.  This can detect a disorder before a baby is born.
 An ultrasound test is used to determine if the fetus is at
a high or low risk from a genetic disorder.
 Disorders are diagnosed by examining a small amount
of fetal cells.This carries a small risk to the fetus.
 If diagnosed early in the pregnancy, there is still the
possibility of abortion.
 Prenatal screening is sometimes seen as controversial.

23.  Newborns are tested for diseases and early
diagnoses allows for immediate treatment.
 A blood sample is tested for genetic disorders.
 In most of the USA, newborn screening is
mandatory, unless parents have a religious
objection to it.
 Sometimes residual blood samples are used for
genetic research, as long as the samples are
kept anonymous.

24.  This involves testing prospective parents for diseases
that they show no symptoms of, but may carry a
recessive gene for.
 A blood sample or cheek cell sample is analysed to
determine whether either parent carries a faulty gene.
 If both parents carry a specific faulty gene, the chance
of the fetus receiving the gene from both parents is
25%, and the chance of being a carrier is 50%.
 If both parents carry a faulty gene, they may decide to
have prenatal testing on the fetus.

25.  Preimplantation screening: Screening
embryos fertilised by IVF before they are implanted
into the uterus.
 Presymptomatic screening: Screening to
predict adult-onset diseases such as Huntington’s
disease.
 Presymptomatic screening: Screening to
estimate the risk of developing cancer or Alzheimer’s
disease as an adult.
 Forensic/Identity testing: Screening to eg.
determine the father of an individual (paternity test).