Prof. ‘Segun Adebami MB.ChB(ife), FWACP Paed

Professor of Paediatrics and Neonatology, College of Health Sciences, LAUTECH, Osogbo,

Nigeria

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Genetics• Branch of science that deals with study of genes

• Genetic diseases include:

– Congenital malformations

– Chromosomal syndromes

– Single gene disorders

• Genetic diseases may result from biochemical derangement in the gene formation e.g substitution of a single amino acid in sickle cell diseases

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Chromosome Rod shaped bodies which appear in the nucleus of a

cell at the time of cell division

Contains genes

Normal human has 46 chromosomes (a diploid) i.e 23 pairs. 23 is the number of chromosome in a gamete

22 Pairs of autosomes and 2 sex chromosomes

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Gene• Biologic unit of heredity, self-reproducing • Located in a definite position (locus) on a particular

chromosome• Dominant gene: gene that produces an effect in the

organism once present regardless of the state of the corresponding allele

• Recessive gene: gene that will produce an effect in the organism only when transmitted by both parents.

• Sex-linked gene: gene that is carried on X or Y Chromosome

• Structural gene: Gene that govern the formation of an enzyme

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Types of genetic disorders Single mutant gene

Abnormalities of the chromosomes

Multifactorial inheritance

Cytoplasmic inheritance

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Single mutant gene 4 pattern of mendelian inheritance

Abnormalities with Autosomes

Autosomal recessive

Autosomal dominant

Abnormalities with Sex Chromosomes

X-linked recessive

X-linked dominant

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Autosomal Recessive• Child of 2 heterozygous parents has a 25% chance of

being homozygous i.e affected

• Males are females are affected with equal frequency

• Affected individuals are almost always born in only 1 generation of a family

• Children of the affected (homozygous) person are all heterozygous (carrier) of the trait

• Children of the homozygous (affected) can be affected only if the spouse is a heterozygous only

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Autosomal Recessive

• Every human being probably has several rare, harmful recessive gene

• Single mutant genes are frequently not identifiable by laboratory tests, usually heterozygous adults learn about the harmful recessive gene after the birth of a homozygous (affected) child

• Related parents are much more likely to be heterozygous for the same harmful recessive gene because of common ancestor, consanguineous matings/marriage is therefore harmful

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Examples of Autosomal Recessive• Sickle Cell disease

• Beta Thalassemia

• Galatosaemia

• Phenyketonuria

• Congenital adrenal hyperplasia

• Spinal muscular atrophy

• Wilson’ disease

• Ataxia telengectasia

• Albinism

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Autosomal Dominant Both male and female are both affected

Transmission occurs from one parent to child

Risk is 50% that an offspring of the affected person will inherit the abnormal chromosome

Mutant gene can arise by spontaneous mutation

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Examples of Autosomal Dominant• Achondroplasia

• Polycystic kidney disease

• Myotonic dystrophy

• Huntingtons chorea

• Oseogenesis imperfecta

• Crouzon syndrome (craniosynostosis)

• Neurofibromatosis

• Retinoblastoma

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X-linked Recessive• Only males are clinically affected

• Affected males are related through carrier females

• All daughters of affected males do not have the mutant/ abnormal gene

• Affected males do not have affected sons but may have affected grandsons born to carrier females

• Female carrier has 50% chance of giving her chromosomes bearing abnormal mutant gene to each of her children

• Each daughter of a carrier has a 50% chance of being a carrier

• Each son has a 50% chance of inheriting the mutant gene

• In each pregnancy, the female carrier has a 25% chance of having an affected son

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Lyonization.

• Note, initially, both X-xsome of a female zygote are active but random inactivation of a portion of one of x-xsome in each cell occurs in fetal development. The inactivated X i(though replicates later) forms the sex chromatin mass or Barr body observed in the nucleus of a cell near the nuclear membrane.

• Lyonization protects the female carrier from the effext of the X-linked recessive mutant gene

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Examples of X-linked Recessive• Haemophylia A

• Haemophylia B

• Duschenne/Becker muscular dystrophy

• Testicular feminization syndrome

• Ocular albinism

• Diabetes insipidus (nephrogenic)

• Ichthyosis

• Retinitis pigmentosa

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X-linked Dominant• Both males and females are affected

• Males are often more severely affected because of homozygosity for X-Xsome

• The disorder is transmitted from generation to generation

• All daughters of an affected father will be affected

• None of the sons of the affected father will be affected

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Examples of X-linked Dominant Vitamin D resistant rickets

Incontinentia pigmenti

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Multifactorial inheritance• This refers to the process in which a disease or

abnormality is the result of additive effect of one or more abnormal genes and environmental factors

– Similar arte of reccurrence among all first degree relatives (parents, siblings and offsprings of affected infant)

– Sex predilection e.g pyloric stenosis in 1st born males

– Influence of environment e.g G6PD deficiency and exposure to icterogenic agents

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Examples of multifactorialinheritance• Cardiac defects

– VSD,– ASD– PDA– TOF

• Hypertension• Diabetes Mellitus• Obesity• Allergy• Autoimmunity

psychiatric illnesses• Cleft palate

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Chromosomal abnormalities Numerical

Structural

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Numerical Chromosomal abnormalities• Euploid: Cell with the exact multiple of the haploid

number eg 46, 69, 92, etc

• Polyploid: Euploid cells with more than normal diploid number i.e 46 xsomes

• Aneuploid: deviating from one of the deuploid numbers e.g Trisomy where there are 3 homologous xsome instead of a pair

• Monosomy: lack of Xsome for the affected pair

• Non disjunction: Failure of homologous to synapse or to seperate

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Structural Chromosomal abnormalities Abnormalities resulting from xsome breaks and

rearrangement

Deletion

Translocation

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Trisomy 21: Down Syndrome Commonest chromosomal abnormalities

There is presence of an extra No 21 chromosome responsible for the abnormalities

Incidence is 1 in 600 – 800 live births

Types

Non-dysjunctional

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Types of Trisomy 21: Down Syndrome Non-dysjunctional (Regular) –94-95%

47XX +21, 47XY +21

Non d

Translocation in 3.3 - 4%

Most often on to Xsome 14

More in younger parents

Mosaic in 1- 2.4%

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Maternal age and Regular Down 15-29 years 1:1,500

30 -34 years 1:800

33 – 39 years 1: 270

40 – 45 years 1 :100

45 years & above 1 :50

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Constant Features Hypotonia

Mental subnormality

Developmental delay

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Characteristic /Typical Clinical Appearance Other features

Small stature

Hypotonicity

Hyperflexibility of joints

Large and protruding tongue

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Down syndrome: Craniofacial Features• Occiput

– Microcephaly– Flat (brachycephaly)– Nose is small– External auditory meatus may be small – Partial deafness– Large anterior frontannel & late in closing– Short neck– High-arched palate

• Eyes– Slant upward laterally– Congenital cataract– strabismus– Small white spots (Brushfield spots) seen in the iris– Prominent epicanthic fold

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Down syndrome: Features• Hands

– Single transverse palmar crease (Simian crease)

– Short & stubby fingers

– Broad hand

– Incurving little finger (Clinodactylyl)

– Widened gap between the 1st (great) and 2nd toe

– Shallow acetabulum

• Genital– Small penis

– Crytochordism

– Infertilility

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Down syndrome: Features• Heart

– Congenital heart defect (Endocardial cushion defect/ atrioventricular septaldefect: ASD, VSD, Tetralogy of Fallot, TOF)

• Gastrointestinal– Small teeth– Irregularly erupted teeth– Tracheoesophagealfistula (TOF),– Malrotation– Pyloric stenosis– Annular pancreas– Intestinal atresia

• Duodenal atresia• Jejunum atresia etc

– Imperforate anus– Hirschsprung disease– exomphalus

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Down syndrome: Features• Haematologic

– Thrombocytopenia– Macrocytosis– Prone to acute lymphoblastic leukaemia– Iron deficiency – Humoral & cellular immunde disorders– Reduced IgM– Reduced T cell function

• Skin– Rough/hyperkeratotic– Fine hair & reduced pubic hair post-pubertal– Alopecia – Vitiligo

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Down syndrome: Features Endocrine

Hypothyroidism in 30%

Hyperthyroidism

Pituitary tumours

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Edward’s Syndrome: Trisomy -18• Incidence 1:8000

• Usually born post-term

• Male: Female = 1:4

• Constant Features

– Hypertonia

– Failure to thrive

– Mental subnormality

– Low birth weight and failure to thrive

– Female preponderance

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Edward’s syndrome Features• Craniofacial

– Prominent occiput

– Micrognathia

– Low set, malformed ears

– Cleft lip &/ palate

• Heart

– CHD: VSD, PDA

– Short sternum

– Diaphragmatic hernia

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Edward’s Syndrome: Trisomy -18 Features• Musculoskeletal

– Felexion deformity of fingers

– Simian crease

– Hypoplastic fingernails

– Short dorsiflexed big toes

– Rockerbottom feet/ equinovarus

• Genitourinary– Horseshoe kidney

– Cryptochordism

Prognosis is GRAVE

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Patau’s Syndrome: Trisomy -13 Features Incidence is 1:20,000

Constant Features

Low birth weight &failure to thrive

Mental subnormality

Capillary heamangiomas

Persistent fetal haemoglobin

Neutrophils with nuclear projections

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Patau’s Syndrome: Trisomy -13 Features• Microcephaly• Cleft lip& palate• Microphthalmia• Shallow suborbital ridge• Low set malformed ears• Micrognathia• Single umbilical artery• Rockerbottom feet• Congenital heart defect (CHD)

– Septal defects, PDA

• Prognosis is GRAVE

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Abnormalities of deletion in the autosomes: Cri du chat syndrome• Cri du chat (5p-) There is deletion in the position of short

arm of chromosome position 5

• Cry of affected infant resemble that of a kitten (catlike) characterized by high-pitched, tense phonation

• Features

– Low birth weight,

– Mental subnormality

– Hypertelorisn

– Low se malformed ears

– micrognathia

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Abnormalities of Sex Chromosome Turner’s syndrome 45X

Klinefelter syndrome 47

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Turner’s Syndrome 45X• More than 90% are spontaneously aborted• Features

– Low birth weight/ small for age– Short webbed neck– Hypertelorism– Epicanthic fold– High arched palate– Low posterior hair line– Short 4th metacarpal or metatarsal– Lymphoedema (non-pitting oedema) of hands and feet at

birth– Small chest with widely spaced nipples

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Turner’s syndrome features• Short stature• Mental subnormality• Sterility• Sexual infantism• Nail hypoplasia• Lack of secondary sexual charcteristics• Coarctation of aorta• Horseshoe kidney & renal anomalies• Multiple naevi• Have streaked gonads at puberty• Primary amenorrhoea

• Rx : Estrogen supplementation for breast & pubic hair development

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Klinelfeter syndrome• Male hypogonadism with at least 2 X-chromosomes and Y-

chromosome ie 47XXY• Prepubertaly, may appear normal• Features

– Delayed or diminished puberty– Tall stature, long legs (Eunechoid habitus)– Gynaecomastia– Female distribution of fats– Testicular hypoplasia– Azzospermia– Oligospermia– Infertility– Penile size may be normal or reduced

– Rx: Testosterone supplementation

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Management • Chromosomal analysis

• karyotyping

• Ultrasound

• Full blood count

• TSH, TRH, T3,4

• EEG

• Radiograph: CXR, Skull X-ray.

• ECG

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Management Multidisciplinary management

Family management

Patient management

Medical, surgical, Plastic

Hormonal replacement

Genetic counselling

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Genetic counselling A communication process dealing with the human

problems associated with the occurrence or risk of occurrence of a genetic disorder in a family

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Principle of genetic counselling• Have both parents for the discussion• Discuss the medical consequences of the defect/abnormality• Review the family history of each parent to detect genetic risk• Explain/describe genetic basis of the abnormality• Explain the genetic risk of the family• Explain the treatment options available for the affected• Outline possible options to prevent recurrence• Give summary of the discussion to assist them in taking a

decision• Stay in contact with the families to provide new information that

may become available on mode of prenatal diagnosis and treatment option

• May need pictures to conceptualise information

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Genetic Counselling: summary• Ensure diagnosis

• Genetic component of aetiology

• Natural course of the disease

• Management and prognosis

• Risk of recurrence

• Ways to prevent recurrence– Prenatal diagnosis

– Artificial insemination by donor

– Adoption

– contraception

• Stay in touch

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Prenatal Diagnosis Over the last 4 decades, the genetic basis of an

increasing number of diseases is becoming understood. At the same time, safe and effective fetal diagnostic techniques are being developed.

Fetal medicine Only in the past few decades has the fetus been

considered a patient and become the subject of extensive scientific study and attempts at treatment. Fetal medicine is a complex multidisciplinary undertaking with a team

Fetal diagnosis

Fetal Therapy

Prenatal Diagnosis of fetal Abnormalities

• Benefits:

1. Malformation incompatible with life may be terminated.

2. Certain abnormalities may be correctible in-utero.

3. -Provides opportunity to arrange corrective measures before hand.

- offer a chance to be delivered at a place where the required facilities are available.

4. Parents decision to continue pregnancy/ mentally prepare to have a handicapped child.

Classification of Congenital Abnormalities1 Chromosomal Abnormalities: - Trisomy 21 (D.S)

- Trisomy 18 (E.S)

- Trisomy 13 (P.S)

2 Structural Abnormalities: - CNS

- CVS

- GIT

- Bone

- Renal system

3 Genetic Disorders: - Inborn error of metabolism

- Haemoglobinopathies

What Should We Do?• Every pregnancy should be evaluated with the most

definite test.

• Practically & economically not feasible because

expensive

Invasive

Worldwide practice is to carry out

-Screening procedures

-Definite (diagnostic)tests for screening

positive cases

Screening ProceduresThese are:

- Simple

- Cheap

- Least invasive

- safe

- Easily repeatable

Screening Procedures --- Cont.1. History:

- Increasing maternal age

- Congenital anomalies in previous children

- F/Hx.

. Still birth

. Recurrent 1st trimester abortion

. Cousin marriage

Screening Procedures ---Cont.2. Features of current pregnancy:

- Drug intake(antiepileptics e.g. warfarin,

alcohol, smoking)

- Radiation exposure

- Maternal ch. diseases e.g.DM, cardiac, renal

- Uterine fundas large/ small for date

- Decrease fetal movements

- Fetal malpresentation

- Viral infection in early pregnancy

Screening Procedures --- Cont.3. Ultrasonography:

- Screening tool in all trimesters

- At 10-14 weeks if fetal nuchal translucency

- > 2.5 mm- chromosomal anomalies

association

- At 18-20 weeks 75% fetal abnormalities can

be diagnose

Screening Procedures ---Cont.4. Maternal blood tests:

- Maternal Serum alpha fetoproteins:

. Produced by

. Fetus &enter in maternal circulation.

. Yolk sac in first trimester

. Liver in second and third trimester

. Normally increase from 12-32 weeks

. Abnormally raise on fetal capillaries

exposure to amniotic fluid e.g. in NTD.

Maternal S. alpha fetoproteins -cont.

- Raised level in neural tube defect(NTD).

- Screen for NTD at 15-20 weeks if +ve confirm with detailed USG.

- Also raised in following conditions:

. Miscalculated dates . Multiple pregnancies

. Threatened abortion . IUD

. Teratoma . Congenital nephrosis

. Ant. Abdominal wall defects

DIAGNOSTIC TESTS For high risk women on basis of screening tests

An ideal test should be :

- Least invasive

- diagnose c. abnormality in early pregnancy.

- Minimally interfering developing pregnancy

Diagnostic tests are also not risk free.

Counselling• Organize an appointment

• Couple should be present

• Explain:

- Risk of occurance of c. abnormality

- All tests available, their procedure, cost, diagnostic ability and benefits, possible risks

- Possible management plain

• If termination of pregnancy is unacceptable diagnostic tests would be fruitless.

NON INVASIVE TESTS• Ultrasonography:

• Diagnostic USG is different from screening USG,

- It takes longer time

- Dx. Wide range of c. anomalies

- Non invasive and diagnosis at spot possible

- But possible only at large gestational age

• Colour doppler further enhance the capability especially for cardiac malformations and renal agenesis.

INVASIVE TESTSAMNIOCENTESIS:

• Aspiration of amniotic fluid which contain fetal cells

• Fluid can be used for estimation of

- bilirubin level (for fetal haemolytic disease).

- AFP

-Acetyl cholinesterase

• Cells used for karyotyping (Chromosomal dis.)

• Fetal cells-cultured for 3 weeks- karyotyping.

• New technique-PCR, FISH-give result in 48 h.

• Preferred time of test 16weeks of pregnancy.

AMNIOCENTESIS---Cont. Procedure:

Preliminary USG to confirm-duration of gestation, -placental site,- adequacy of liqour (150-200 ml)

Sterilize the abdomen

22 G spinal needle is used.

About 20 cc amniotic fluid is withdrawn.

Give Anti- D to all Rh-ve mothers.

Ask rest for 30 min.& restrict movements for 48h

Amniocentesis

AMNIOCENTESIS---Cont.• Limitations (difficulties)of procedure: if

- Anteriorly placed placenta- Multiple pregnancy.- Maternal obesity- Oligohydramnios

• Risks:- Pregnancy loss 1 % - Bleeding , Infection, - Rupture of membrane - Preterm labour&IUD- Leaking of Amniotic fluid- Increase risk of RDS in newborn

CHORIONIC VILLUS SAMPLING (CVS)• Collection of fragments of placental tissue (chorionic

villi)- cells are examined for Dx. of C.Anomalies.

• Cytotrophoblastic (rapidly dividing) cells are used for direct karyotyping- result available within 24-48 h.

• Chorionic villi are best source of DNA

• CVS can be performed at 10 weeks gestation.

• Indications:

1-DNA analysis for SCD, Thallasemias, CF. hemophillias

2-Chromosomal abnormalities

3-Inborn error of metabolism

CHORIONIC VILLUS SAMPLING• Procedure:

• Trans-abdominal approach preferred –under USG guidance in supine position

• Trans-cervical approach is easy.

• In lithotomy position, sterilize area & Aspiration catheter and biopsy forceps.

• Introduce through Cx. under USG into placental tissue avoiding membrane rupture

• Risks: Pregnancy loss 2-6%

• Before 10 weeks- associated with limb deformities, micrognathia, microglassia

FETAL BLOOD SAMPLING (FBS)• Fetal blood- lymphocyte are rapidly cultured, results within

48-72 hours.

• Indications: 1- Prenatal Dx. DNA available for Cytogenetic studies In failed amniocentesis, and mosaicism in chorion or amniotic fluid.

2-Fetal assessment: for red cell alloimmunization, (Hb;Hc,TrF) Hydrops fetalis, viral infection, platelets alloimmunization

• Unfortunately Associated with highest rate of fetal loss.

• Currently used for blood transfusion in-utero in fetal A.

FETAL BLOOD SAMPLING (FBS)• Procedure : (cordocentesis):

• The sites for FBS are placental insertion of umbilical cord, abdominal insertion of cord, intrahepatic fetal vein and fetal heart.

• Suitable time is 20-28 weeks

• Risks:

- Bleeding from site of puncture

- Cord haematoma

- Fetal bradycardia

- Fetal death

EMBRYOSCOPY & FETOSCOPY Direct visualization of embryo and fetus.

Limited field of vision.

Provide information only about external fetal structures .

NEW MOLECULAR ANALYTIC TECHNIQUES Fetal cell obtained by CVS and Amniocentesis can be

used for prenatal Dx. For congenital anomalies by following new techniques

1- Southern blotting:

Cleavage of chromosomal DNA at specific

sites and used for tests

2- PCR

3- FISH

Polymerase chain reaction (PCR)• Amplify specific DNA and RNA fragments

• Once nucleotide sequence of a region of DNA strand is known, complimentary oligonucleotides & polymerase are added to single strand DNA

• Repeat process 30 times to get adequate DNA

• PCR identify specific DNA sequence for gene mutation & prenatal Dx. at an earlier stage before an embryo transfer in IVF cycle.

FLOURESCENT IN SITU HYBRIDIZATION FISH allows detection & localization of specific DNA

sequence in interphase or metaphase.

Advantage – results available in 24-48 h.

Disadvantage – fail to detect big structural rearrangements

Identify 80% clinically relevant abnormalities, helpful for early decision about further management of affected pregnancies.

MANAGEMENT OF FETAL CONGENITAL ANOMALIES

It is a tedious task, requires skillful, sympathetic & professional approach.

Management options

- Termination of pregnancy

- In- utero management if possible

- Conservative management

POSTPARTUM MANAGEMENT OF C.A.

For better understanding of congenital anomalies

and its impact on future reproductive performance of

couple, following procedures are carried out on

affected babies/ abortusses:

1. Physical examination /postmortem

2. Fetal tissue(blood, skin, placenta) for karyotyping

3. Placenta and membrane for histopathology

4. Placental & baby swab for microbiology & virology.

5. Baby gram (x-rays of whole baby)

6. Baby photograph

THANK YOU FOR LISTENING

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