Transcript Dr . Muhammad Rafique Assist. Prof. Paediatrics College of

Dr . Muhammad Rafique
Assist. Prof. Paediatrics
College of Medicine
K K U Abha K S A
PRENATAL DIAGNOSIS
It introduces option for management. From
interruption of abnormal pregnancies to
prepare for specialized peri-natal care.
PRENATAL Dx.------CONT.
Methods of prenatal diagnosis:
.Maternal blood sampling.
.Fetal ultrasonography.
.Fetal X-ray
.Fetal MRI
.Amniocentesis
.Chorionic villus sampling
MATERNAL BLOOD SAMPLING
• Elevated alpha fetoproteins:
• Twins ,
• intestinal obstruction ,
• neural tube defects.
• Decreased alpha fetoproteins:
• Trisomy 21/ Down synd.
• Elevated chorionic-gonadotropins:
•
Trisomy 21
MATERNAL BLOOD SAMPLING—CONT.
• Deceased chorionogonadotropin:
.Trisomy 13,
.Trisomy 18
• Decreased unconjugated estriol:
.Trisomy 21
FETAL ULTRASONOGRAPHY
Maternal trans-abdominal USG can visualize all
major fetal organs at 16-18 weeks of gestation
and can diagnose disorders like;
Hydrops fetalis , hydronephrosis , neural
tube defects , intestinal obstruction , CHD ,
diaphragmatic hernia , limb reduction
anomalies and growth assessment etc.
CORDOCENTESIS
Fetal blood can be directly sampled in late
gestation through USG guided per-cutaneous
umbilical cord blood sampling & can detect;
.fetal anemia
. Thrombocytopenia
.thalassemia
. Fetal oxygenation
.acid base disorders
.cells for DNA
.fetal hypo-albuminemia
CHORIONIC VILLUS SAMPLING
CVS at 10-12 weeks provides good cytotrophoblast (dividing cells) DNA for
molecular analysis that can be rapidly
karyotyped.
Detection possible for:
Thalassemia, hemophilia A, PKU, CAH.,
alpa-1 antitrypsin deficiency, SCD etc.
Trisomy 21,18,13,turner&klinefelter synd.
AMNIOCENTESIS
Amniotic fluid can be sampled at 10-14 weeks
gestation for fetal cells -can be cultured For
• Cyto-genetics
• Molecular analysis
• Metabolic analysis.
• Alpha-fetoproteins measurement.
Note –complication of miscarriage <1%.
Amniocentesis
INDICATIONS FOR CVS/AMNIOCENTESIS
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Maternal age above 35 years.
Previous child with chromosomal abnormality.
Either parent a translocation carrier.
F/Hx. of genetic disease, Dx. by biochemical or
DNA analysis.
• Parental request for sex determination because
of F/Hx. of X-linked disorder.
• Maternal blood sample show chromosomal abn.
• As a part of work up for fetal anomalies by USG.
GENETIC TESTING
Analysis of genetic material to obtain
information related to individual’s health
status using either chr. analysis or DNA
based testing.
Two types.
1-Linkage analysis
2-Direct mutation analysis
LINKAGE ANALYSIS
It is used if
• Responsible gene is mapped but not yet
identified.
• Impractical to find specific mutation due to
large size & No. of different mutation in a
gene e.g. CF.
DIRECT MUTATION TESTING
• It is preferred to detect gene mutation because
genome sequence is elucidated and
technologies improved.
• It avoids pitfalls of linkage testing by detection
of gene mutation.
• In some disorders all individual have same
mutation. e.g. SCD.
• In some, people have different mutation e.g. CF.
PREDICTIVE GENETIC TESTING
• Testing in individuals who are at risk to
develop a genetic disorder e.g. due to F/Hx.
before developing s/symptoms , especially
which disorders are age dependent and s/s
increase with increasing age , e.g. Huntington
disease, cancer.
• Note-development of disease is not necessary
in every mutation containing person.
GENETIC COUNSELLINIG
• Process by which a person is informed about
possibility of developing a disorder or
transmitting it to his offspring and chances of
his offspring having similar disorder.
• Important steps are ;
.History
.pedigree construction
.physical examination . diagnosis,
.counseling
.follow up
GENETIC OUNSELLING STEPS
• Offer possible help to manage disorder.
• Sex detection & pre-natal Dx.by amniocentesis
to decide parents to have/not the baby.
• Explain outcome statistically for each pregnancy.
• Provide good knowledge about disorder’s
etiology, Dx. and Mx. in discussion.
• Provide new information whenever available.
GENETIC COUNSELLING STEPS
Timing of counseling;
• Not too early (because family still concerned
about welfare of affected individual &
emotionally upset).
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Not too late (because an other at risk fetus
is conceived ).
GENETIC OUNSELLING STEPS
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Careful F/Hx. and pedigree construction
Document pre-natal, pregnancy & delivery Hx.
Review available informations about disorder.
Careful physical exam. of affected individual
and apparently unaffected family individuals.
• Establish accurate Dx. by available tests.
• Mode of inheritance establish and explain.
GENETIC OUNSELLING STEPS
• Therapy and referral;
Some pt. need specialist care e.g . Turner
synd. need endocrinologist evaluation.
• Prevention of complications should be priority
• Support groups;
Provide information about support group that
provide funds for research on specific disorder
• Nondirective counseling;
INDICATIONS OF GENETIC COUNSELLING
• Advanced parental age;
.Maternal >35 years
.Paternal >50years
• Previous child with F/Hx. of
.congenital abnormality
.Dysmorphology
.Isolated birth defects
.metabolic disorder
.Chromosomal abnormality
.single gene defect
INDICATIONS OF GENETIC OUNSELLING
• Adult onset disease/pre-symptomatic testing ;
.cancer
.Huntington disease
• Consanguinity
• Teratogenic exposure
• Repeated miscarriage or infertility
INDICATIONS OF GENETIC COUNSELLING
• Pregnancy screening abnormality
.maternal high alpha fetoproteins
.fetal USG
.fetal karyotyping
• Heterozygote screening based on ethnic risk;
.sickle cell anemia
.thalassemia
• Follow up to abnormal genetic testing
MANAGEMENT &TREATMENT OF
GENETIC DISORDERS
• GD mostly chronic.
• Few are amenable to curative therapies.
• Provide information about GD, G.counseling ,
anticipatory guidance and appropriate
medical surveillance.
• Surgical Mx. is available for many congenital
anomalies that are predisposition to tumours.
MANAGEMENT &TREATMENT OF
GENETIC DISORDERS
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PHYSIOLOGICAL THERAPIES;
Attempts to ameliorate phenotype of a GD.
Underlying GD not altered by treatment.
Used in inborn error of metabolism e.g.
dietary manipulation in PKU, avoiding
phenylalanine diet.
.Enzyme supplement for
methyl-malonic-acidemia.
.Bisphosphonate for osteogenesis imperfecta.
MANAGEMENT & TREATMENT OF
GENETIC DISORDERS
PHARMALOGICAL THERAPIES;
• Use of pharmaceuticals to remove ammonia
in urea cycle defect.
• It directly target defective cellular pathway
that is altered by abnormal /missing gene.
Replacement therapy ; e.g.
.cystic fibrosis
.Gauscher disease
MANAGEMENT & TREATMENT OF
GENETIC DISORDERS
Organ transplant;
• E.g. transplant of liver in inborn error of
metabolism.
• Transplant of bone marrow in many
haemotological disorders.
Gene therapy;
• Less invasive mean of achieving cure of a GD.
PREVENTION OF GENETIC DISORDERS
• Some GD has gene defect + environmental
factors impact e.g. multifactorial disorders.
• Prevention possible by
.avoiding inciting environmental factor e.g.avoid
maternal phenytoin use to avoid fetal CHD.
.By instituting treatment that reduce risk e.g.
maternal use of folic acid to avoid fetal neuraltube defect.
NEWBORN SCREENING TESTS
1-Chromosomal analysis;
Body cells are cultured ,arrested in mitosis in
metaphase .Chromosome first evaluated
microscopically then images are captured by
video camera and stored on a computer .
Homologous chr. are paired , arranged into
Karyotype. Chromosomes are exposed to a
hypotonic solution, fixed and stained with
“ trypsin Giemsa”which produces dark and light
bands for detail study.
NEWBORN SCREENING TESTS
2-FISH (fluorescence in situ hybridization);
- Used to identify , presence, absence, or
rearrangement of specific DNA segment.
- It involve unique DNA sequence labeled with a
fluorescent dye , which is exposed to single
stranded DNA on a microscopic slide.
NEWBORN SCREENING TESTS
FISH---cont.
-Probe, pairs with its complementary DNA
sequence and can be visualized by
fluorescence microscopy.
- It is particularly useful for detecting very
small deletion which not detectable by band
analysis.
NEWBORN SCREENING TESTS
3-Spectral karyotyping (SKY) & multicolour FISH;
• 24 different chr. Painting probes are used for chr.
and labeled with different combination of 5
fluorescent dyes(which omit at different
wavelength).
• 23 pair of chr. have unique spectra of
wavelength fluorescence.
• Especially used to identify complex chr.
Re-arrangement found in tumours.
NEWBORN SCREENING TESTS
4-COMPARITIVE GENOMIC HYBRIDIZATION(CGH)
-FISH based method to measure differences in
a particular DNA sequence / chr. segment
between two different DNA samples.
-Pt’s DNA labeled with green fuorescent dye &
normal reference DNA with red .
-Equal amount of two mixed &used for FISH.
NEWBORN SCREENING TESTS
4-COMPARITIVE GENOMIC HYBRIDIZATION(CGH)
-Ratio of green to red fluorescence measured
along each chr.
-Region of amplification of pt’s DNA shows
excess green fluorescence & region of loss of
pt’s DNA shows excess of red fluorescence.
-If green and red same 1:1,chromosome would
appear yellow.