Transcript EMBRYOLOGY OF THE TWINS AND TERATOLOGY by Sudarjati

EMBRYOLOGY OF
THE TWINS AND
TERATOLOGY
dr.RB.Soeherman H M.Kes
THE TWINS
I. Dizygotic Twins
II. MonozygoticTwins
III. Conjoined MonozygoticTwins
I. Dizygotic Twins
-Fraternal twins = heterolog
-They may or may not have different sex
-The individual members have no more
resemblance than brothers or sisters of
ages
different
-They result from simultaneous shedding of two
oocytes and the fertilization by two different
spermatozoa
-Both zygotes implant individually in the uterus
and each develops its own placenta, its own
amnion, and its own chorionic sac
-Sometimes, however, the two placentas are
located so close together that fusion occurs
-Similarly the walls of the chorionic sacs may also
come into close apposition and
fuse
II.Monozygotic Twins
- Uniovuler = identical twins = homolog
twins
-They result from the splitting of the
zygote at various stages of development
- The earliest separation occur at two cell
stage  both blastocysts implant
separately and each embryo has its own
placenta and chorionic sac
- In most case the splitting of the zygote
occurs at the early blastocyst stage
- In rare cases, the separation occurs at the
stage of the bilaminar germ disc just
before the appearance of the primitive
streak
- Some times large anastomoses cause
circulatory disturbances, resulting in one
large and one small partner
- Blood groups, fingerprint, sex and external
appearance such as eye and hair color are
the same
- Have a common placenta and common
chorionic cavity, but separate amniotic
cavity
Conjoined monozigotic twin
-If the embryonic disc does not devide completely
or adjacent embryonic discs fuse,various types of
conjoinned MZ twins may form.
Parasitic twins:small bowel with right lower limb
in parasitic twin.
Parasitic fetus:lower limb and pelvis attached to
the thorax of infant
Dicephalic(two head) conjoined twin
-The partners of monozygotic twins are
connected to each other only by a
common skin bridge or by a common
liver bridge (Siamese twins)
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20
TERATOLOGY
CONGENITAL MALFORMATION
• Teratology: the study of birth defects, their
causes and investigations pertaining to both
structural and behavioral abnormalities
• The incidence: 0.75 to 1.98 % in studies of
official records and birth certificates
• When compared with data from hospital and
clinic birth records, variation of 1.43 to 3.3 %
are probably more accurate.
THE CAUSE OF CONGENITAL
MALFORMATIONS
• I. Enviromental factors
• II. Chromosomal and genetic factors
I. Enviromental factors
A. Infectious Agents
1. Rubella or German Measles
German measles affecting pregnant women in the
early stages of gestation could lead to congenital
malformations in the offspring
• Rubella virus can cause malformations of the:
- eye (cataract and microphthalmia)
- internal ear (congenital deafness due
destruction of the organ of Corti)
- heart (PDA:persistence of the ductus
arteriosus as well as atrial and ventricular
septal defects:VSD)
- and occasionally of the teeth (enamel layer)
• The virus may also be responsible for some
cases of brain abnormalities and mental
retardation
 Virus also causes IUGR (intrauterine growth
retardation),
myocardial damage, and
vascular abnormalities
 The type of malformation is determined by
the stage of embryonic development at
which infection occurs:
* Cataracts result from infection during the
6th week of pregnancy
* Deafness from infection during the 9th
week of pregnancy
* Dental deformities between the 6th and
9th weeks
* Abnormalities of the central nervous
system follow infection in the 2nd
trimester
* Cardiac defects follow infection in the
5th to 10th weeks
2. Cytomegalovirus
- The congenital cytomegalic inclusion
disease is the result of a human
cytomegalovirus infection acquired in utero
from an asymptomatically infected mother
- The principal findings of the infection are:
microcephaly, cerebral calcifications,
blindness and chorioretinitis, and
hepatosplenomegaly
- Initially the disease was recognized only at
autopsy and was based on the presence of
enlarged cells, with large nuclei containing giant
inclusion bodies
- The inclusion bodies in cells lining of renal
tubules, and may be present in the urine
- When the embryo is affected at an early stage of
development the damage is so severe that it is
unable to survive
3. Herpes Simplex Virus
-The infection is transmitted close to the
time of delivery, and the abnormalities
are: microcephaly, microphthalmos, retinal
dysplasia, hepatosplenomegaly and
mental retardation
-The child acquires the infection from the
mother at birth as a venereal disease and
the symptoms of the disease then develop
during the first 3 weeks of age
4. Other Viral Infections and Hyperthermia
- Malformations following maternal
infections with measles, mumps, hepatitis,
poliomyelitis, chickenpox, ECHO,
Coxsackie, and influenza virus have been
described
- The other infectious agents is that most are
pyrogenic and increased body temperature
(hyperthermia) has been implicated as a
teratogen
5. Toxoplasmosis
-The affected child may have cerebral
calcification, hydrocephalus, or mental
retardation
-The disease is usually unrecognized in
pregnant women
6. Syphilis
-In the offspring syphilis may lead to
congenital deafness and mental
retardation
-Organs such as the lung and liver are
characterized by diffuse fibrosis
B. Radiation
- Treating pregnant women with large doses of
roentgen rays or radium cause malformations:
microcephaly, skull defects, spina bifida,
blindness, cleft palate and defects of the
extremities
- The nature of the malformation depends on the
dose of radiation and the stage of development
at which the radiation is given
-The offspring of Japanese women pregnant at the
time of the atomic bomb explosions over
Hiroshima and Nagasaki revealed that among the
survivors:
- 28 % aborted,
- 25 % gave birth to children who died in
their 1st year of life, and
- 25 % of the surviving children had
abnormalities of the central nervous system
C . Chemical Agents
1. Thalidomide
- An antinauseant and sleeping pill
- The defects produced by thalidomide are
absence or gross deformities of the long bones:
amelia and meromelia (total or partial absence
of the extremities), intestinal atresia and
cardiac abnormalities
2. Aminopterin
- This compound belongs to the antimeteabolites and an antagonist of folic acid
- It has been used during early pregnancy to
induce therapeutic abortion in women
suffering from tuberculosis
- The defects are anencephaly, meningocele
hydrocephalus, and cleft lip and palate
3. Anticonvulsants
- Diphenylhydantoin (phenytoin) and trimethadion, which are used by epileptic women
- Teratogenic potential
- The major malformations such as:
- heart abnormalities,
- facial clefts, and
- microcephaly
- Specifically, diphenylhydantoin produces
broad spectrum of abnormalities, includimg
- craniofacial defects,
- nail and digital hypoplasia,
- growth abnormalities and mental
deficiency
- These defects constitute a distinct pattern of
dysmorphogenesis known as the
“fetal hydantoin syndrome”
4. Trimethadione
- Used in treatment of petit mal seizures
- Teratogenic
- These drugs produced a characteristic pattern
of abnormalities including:
- malformed ears,
- cleft palate,
- cardiac defects,
- urogenital and skeletal anomalies
which are collectively referred to as the
“trimethadione syndrome”
5. Antipsychotic and antianxiety agents
Antipsychotic agents:
- phenothiazine and lithium: teratogens
- High risk if these agents are used during
pregnancy
Antianxiety agents:
- diazepam (Valium), chlordiazepoxide and
Meprobamate,
- increase in cleft lip with or without cleft
palate in offspring from mothers taking
the drug during pregnancy
A number of other compounds which might be
damaging to the embryo or fetus:
- Propylthiouracil and potassium iodide (goiter and
mental retardation),
- Streptomycin (deafness),
- Sulfonamides (kernicterus),
- Imipramine, antidepressant (limb deformities)
- Tetracyclines (bone and tooth anomalies),
- Amphetamines (oral clefts and cardiovascular
abnormalities),
- Walfarin, anticoagulant (chondrodysplasia and
microcephaly) and
- Quinine (deafness)
- Aspirin (salicylates), the most commonly
ingested drug during pregnancy, is potentially
harmful to the developing offspring when used
in large doses
6. The increasing problems in todays society is the
effect of social drugs such as
- LSD (Lysergic acid diethylamide),
- PCP( Phencyclidine, angel dust ),
- Marijuana, alcohol and cocaine.
In the case of LSD, limb abnormalities and
malformations of the central nervous system have
been reported
- The heavy smoking during pregnancy causes
small babies
The defects of maternal alcohol ingestion:
- Craniofacial abnormalities (short palpebral
fissures and hypoplasia of the maxilla ),
- Limb deformities (altered joint mobility and
position), and
- Cardiovascular defects (ventricular and
septal abnormalities)
 Together with mental retardation and
growth deficiency, make up the
“fetal alcoholic syndrome”
7. Isotretinoin (13-cis-retinoic acid)
- an analogue of vitamin A
- the drug is prescribed for the treatment of
cystic acne and other chronic dermatoses
- but it is highly teratogenic
- been shown to cause a pattern of
malformations as the “isotretinoin or
vitamin A embryopathy”
D. Hormones
1. Androgenic agents
- The synthetic progestins which are frequently
used during pregnancy to avert abortion
- Ethisteron and norethisterone have
considerable androgenic activity, and many
cases of masculinization of the genitalia in
female embryos
- The abnormalities consisted of an enlarged
clitoris associated with varying degrees of
fussion of the labioscrotal folds
2. Diethylstilbestrol
- A synthetic estrogen, was commonly used to
prevent abortion
- Increased incidence of carcinoma of the
vagina and cervix following exposure to the
drug in utero
- A high percentage of these exposed women
suffer from reproductive dysfunction which
appears to be due in part to congenital malformations of the uterus, uterine tubes, and
upper vagina
-Male embryos exposed in utero can also be
affected, as evidenced by an increase in malormation of the testes, and abnormal sperm
analysis
-In contrast to females, males do not
demonstrated an increased risk of developing
carcinomas of the genital system
3. Cortisone
In experiment: Cortisone injected into mice and
rabbit at certain stages of pregnancy causes a
high percentage of cleft palates in the offspring
4. Maternal diabetes
- Disturbances in carbohydrate metabolism
during pregnancy in diabetic mothers cause a
high incidence of stillbirths, neonatal deaths,
abnormally large infants, and congenital
malformations
- A variety of malformations have been
observed, including:
- cardiac, skeletal and central nervous
system anomalies
- skeletal defects also occur and consist
of partial or complete agenesis of
sacral vertebrae in conjunction with
hindlimb hypoplasia
- If women with previous histories of congenital
defects and indications of disturbed carbohydrate metabolism were treated with insulin or
thyroid, or both, subsequent pregnancies
resulted in fewer miscarriages, stillbirth, and
infants with congenital malformations
E. Nutritional deficiencies
- Endemic cretinism, which is related to maternal iodine deficiency have been found in
humans
F. Hypoxia
- Children born at relatively high altitudes are
usually lighter in weight and smaller than those
born near or at sea level
- Women with cyanotic cardiovascular disease
often give birth to small infants, but usually
without gross congenital malformations
G. Enviromental Chemicals: organic mercury
In Japan:
- The fish contained an abnormally high level of
organic mercury, which was spewed into
Minamata Bay, and other coastal water of
Japan by large industries
 A number of mothers with diets consisting
mainly of fish had given birth to children
with multiple neurological symptoms
resembling cerebral palsy
In the United States:
- when seed corn sprayed with a mercurycontaining fungicide was fed to hogs, and the
meat was subsequently eaten by a pregnant
women  several thousand babies were
affected
Actions of Teratogens
1.The stage of embryonic development
determines the susceptibility to teratogenic
factors.
2.The effect of a teratogenic factor depends
on the genotype.
3. A teratogenic agent acts in a specific way
on a particular cell metabolism.