MOSAICISM IS A CONDITION IN WHICH CELLS WITHIN THE SAME INDIVIDUAL HAVE A DIFFERENT GENETIC MAKEUP. THE CYTOGENETIC ABNORMALITY CONFINED TO PLACENTA, MOST OFTEN THE TRISOMY STUDIED BY CVS(CHORIONIC VILLUS SAMPLING), DURING TO 9-11 WEEKS OF GESTATION IS KNOWN AS THE CONFINED PLACENTAL MOSAICISM.

1. TOPIC: PSEUDOMOSAICISM AND CONFINED PLACENTAL
MOSAICISM
PRESENTED BY- PRANGYA PARAMITA JENA
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2. MOSAICISM
.MOSAICISM IS A CONDITION IN WHICH CELLS WITHIN THE SAME INDIVIDUAL HAVE A
DIFFERENT GENETIC MAKE UP.
. MOSAICISM PHENOMENON WAS DISCOVERED BY CURT STERN.(DEMONSTRATED
RECOMBINATION IN NORMAL MEIOSIS ,CAN ALSO TAKES PLACE IN MITOSIS).
. INDIVIDUALS SHOWING MOSAICISM ARE REFFERED TO AS MOSAICS. MOSAICS CAN BE
CAUSED BY DNA MUTATIONS, EPIGENETIC ALTERATIONS OF DNA, CHROMOSOMAL
ABNORMALITIES(CHANGE IN THE CHROMOSOME NUMBER AND THE STRUCTURE) AND
THE SPONTANEOUS REVERSION OF INHERITED MUTATIONS.
. MOSAICISM IS ASSOCIATED WITH CHANGES IN EITHER NUCLEAR OR MITOCHONDRIAL
DNA.
. AN INDIVIDUAL WITH TWO OR MORE CELL TYPES DIFFERING IN THE CHROMOSOMAL
NUMBER OR STRUCTURE IS EITHER MOSAIC OR CHIMERS.

3. MOSAICISM
TRUE MOSAICSM
A CHROMOSOMAL MOSAICSM
IS WHEN TWO OR MORE
ABNORMAL CELLS LINES ARE
DETECTED IN TWO OR MORE
CULTURE FLASKS FROM THE
SAME INDIVIDUAL (DIFFERENT
PRIMARY CULTURES)
PSEUDO MOSAICSM
A CHROMOSOMAL MOSAICSM
USED TO DESCRIBE TWO
ABNORMAL CELL LINES THAT ARE
FOUND IN ONLY ONE CULTURE
FLASK(ASSOCIATED WITH ONLY
ONE PRIMARY CULTURE)
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4. .IF THE TWO CELL TYPES ARE ORIGINATED FROM A SINGLE ZYGOTE, THE
INDIVIDUAL IS MOSAIC.
.AND WHEN THE TWO CELLS ORIGINATED FROM TWO OR MORE ZYGOTES WHICH
ARE SUBSEQUENTLY FUSED, THE INDIVIDUAL IS A CHIMERA.(SINGLE ORGANISM
WITH DISTINCT GENOTYPES).
.THUS, CHROMOSOMAL MOSAICISM IS THE BIOLOGICAL PHENOMENON THAT
INDICATING THE PRESENCE OF TWO OR MORE CHROMOSOMALLY DIFFERENT CELL
LINES IN AN INDIVIDUAL ARISING FROM A SINGLE ZYGOTE.
.MOSAICISM CAN EXIST IN BOTH CELLS (SOMATIC AS WELL AS THE GERM LINE
CELLS).
.THE SOMATIC AND GERM LINE MOSAICISM REFERS TO THE PRESENCE OF
GENETICALLY DISTINCT GROUPS OF CELLS WITHIN THE SOMATIC AND GERM LINE
TISSUES. 4

5. .MOSAICISM EVENT OCCUR DURING DEVELOPMENT;
THERE IS A POSSIBILITY THAT BOTH SOMATIC AND GERM LINE CELLS WILL BE
MOSAIC. HERE, IN THIS CASE BOTH SOMATIC AND GERM LINE TISSUE
POPULATIONS WOULD BE AFFECTED AND AN INDIVIDUAL COULD TRANSMIT THE
MOSAIC GENOTYPE TO HIS/ HER OFFSPRINGS.
.MOSAICISM EVENT OCCUR DURING LATER DEVELOPMENT;
THERE IS A POSSIBILITY IT COULD EITHER AFFECT THE GERM LINE / SOMATIC CELL
POPULATION . IF THE MOSAICISM OCCURS ONLY AT THE SOMATIC CELL
POPULATION; THE PHENOTYPIC EFFECT WILL DEPEND ON THE EXTENT OF THE
MOSAIC CELL POPULATION , BUT THERE COULD BE NO RISK OF PASSING ON THE
MOSAIC GENOTYPE OF OFFSPRING.
BUT IF MOSAICISM OCCURRED ONLY IN THE GERM LINE CELL POPULATION , THE
INDIVIDUAL WOULD BE UNAFFECTED BUT THE OFFSPRING COULD BE AFFECTED.
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6. CAUSES OF MOSAICISM:
1. ERROR IN MITOSIS;
ITS HOW A BABY GROWS IN THE WOMB.MITOSIS CAUSES THE NUMBER OF CHROMOSOMES
TO DOUBLE TO 92 AND THEN SPLIT HALF BACK TO 46.
THIS PROCESS IS REPEATED CONSTANTLY AS THE BABY GROWS.
IF THERE IS AN ERROR IN MITOSIS , A CELL DOESN’T SPLIT EVENLY INTO TWO CELLS.THE
RESULT IS THAT SOME CELLS HAVE NORMAL NUMBERS OF 46 CHROMOSOMES AND OTHER
CELLS WILL HAVE MORE (47) OR FEWER (45) CHROMOSOMES.
2. ANAPHASE LAGGING;
A COMMON WAY FOR INITIATION OF THE MOSAICISM. IT’S A CONSEQUENCE OF AN EVENT
DURING CELL DIVISION WHERE THE SISTER CHROMATIDS DO NOT PROPERLY SEPARATE
FROM EACH OTHER BECAUSE OF THE IMPROPER SPINDLE FORMATION.THE MIGRATION OF
THE CHROMOSOMES OR THE CHROMATIDS DOESN’T TAKES PLACE , AS A RESULT ANAPHASE
LAG WILL CAUSE ONE DAUGHTER CELL TO RECEIVE A COMPLETE SET OF CHROMOSOMES
WHILE OTHER LACKS ONE PAIRED SET OF CHROMOSOMES (MONOSOMY).
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7. 3.NON-DISJUNCTION;
REFERS TO FAILURE OF THE HOMOLOGOUS CHROMOSOMES / SISTER
CHROMATIDS TO SEPARATE PROPERLY DURING CELL DIVISION.
NONDISJUNCTION RESULTS IN DAUGHTER CELLS WITH ABNORMAL
CHROMOSOME NUMBERS LEADING TO ANEUPLOIDY.
4.ENDOREDUPLICATION;
ALSO CALLED AS ENDOREPLICATION, IS A REPLICATION OF THE NUCLEAR
GENOME IN THE ABSENCE OF THE MITOSIS AS A RESULT LEADING TO THE
ELEVATION OF THE NUCLEAR GENE CONTENT AND RESULTING INTO HAVING
MORE THAN TWO PAIRED CHROMOSOMES(POLYPLOIDY).
POLYPLOIDY CONDITION IS MORE SIGNIFICANT IN PLANTS, BUT POLYPLOIDY DO
OCCURS IN SOME TISSUES OF THE ANIMALS,LIKE THE HUMAN MUSCLE CELLS.
WHICH IS REFFERED AS THE ENDOPOLYPLOIDY.
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8. PREDICTING MOSAICISM( METHODS OF ASCERTAINMENT):FACTORS
CONSIDERED WHEN TRYING PREDICT THE OUTCOME OF MOSAICISM;
.CVS(CHORIONIC VILLUS SAMPLING) SHOWS THAT THE PLACENTA IS
AFFECTED.
. AMNIOTIC FLUID SUGGESTS THAT ATLEAST ONE FETAL TISSUE MAY
BE AFFECTED.
. FETAL BLOOD SAMPLING CONFIRMS THE DIAGNOSIS OF THE
CHROMOSOMAL MOSAICISM.
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9. CONFINED PLACENTAL MOSAICISM:
.THE CYTOGENETIC ABNORMALITY CONFINED TO PLACENTA, MOST OFTEN THE
TRISOMY STUDIED BY CVS(CHORIONIC VILLUS SAMPLING), DURING TO 9-11
WEEKS OF GESTATION IS KNOWN AS THE CONFINED PLACENTAL MOSAICISM.
.IT HAS BEEN ESTIMATED THAT APPROXIMATELY 16 TO 21 % OF PREGNANCIES
SHOWS THE PRENATAL AND PERINATAL COMPLICATIONS. CPM IS
APPROXIMATELY DETECTED IN 1-2% OF ONGOING PREGNANCIES.
.CPM REPRESENTS TISSUE SPECIFIC CHROMOSOMAL MOSAICISM AFFECTING
THE PLACENTA ONLY. THE CLINICAL OUTCOME OF CHROMOSOMAL MOSAICISM
IS STRONGLY DEPENDENT ON THE SPECIFIC CHROMOSOME INVOLVED AND THE
NUMBER OF TRISOMIC CELLES INVOLVED IN BOTH THE FETUS AND PLACENTA.
.THE DIAGNOSIS OF THE CONFINED PLACENTAL MOSAICISM IN A CVS SAMPLE, IS
MADE AFTER THE DIAGNOSIS OF THE SECOND PRENATAL TESTING i.e AMNIOTIC
FLUID CULTURE OR FETAL BLOOD CULTURE ANALYSIS. 9

10. PATHOGENESIS OF CPM:
THERE ARE TWO WAYS OF OCCURRENCE CONFINED PLACENTAL MOSAICISM;
Mitotic CPM - Mitotic non-disjunction can occur in a trophoblast cell or a non-
fetal cell from the inner cell mass creating a trisomic cell line in the tissue which
is destined to become the placental mesoderm.
Meiotic CPM - Alternatively, CPM can occur through the mechanism of trisomic
rescue. If a trisomic conception undergoes trisomic rescue in certain cells,
including those that are destined to become the baby, then the remaining
trisomy cells may be confined to the placenta.
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11. SOURCE:Confined placental mosaicism
Dagmar K Kalousek, Michel Vekemans
JMed Genet 1996;33:529-533
TYPES OF CPM(CONFINED PLACENTAL MOSAICISM):
1.TRISOMIC CYTROPHOBLAST & DIPLOID CHORIONIC
STROMA- The error occurs in a trophoblast cell, and
thus only trophoblast cells are affected. This type of
mosaicism is most often associated with normal
pregnancy outcome.
2. DIPLOID CYTOTROPHOBLAST AND TRISOMIC
CHORIONIC STROMA-The error occurs in a non-fetal
cell of the inner cell mass. This trisomy is confined to
the chorionic villus stroma. This type of mosaicism is
described in normal pregnancies and is sometimes
associated with delayed growth of the fetus.
3. TRISOMIC CYTROTROPHOBLAST AND CHORIONIC
STROMA- Trisomic cells are seen in trophoblast cells
and the villus stroma, but are absent in the embryo.
This type of mosaicism is more commonly associated
with delayed growth in the fetus.
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12. PROGNOSTIC INCLUDES:
. Most pregnancies that are diagnosed with confined placental mosaicism continue to
term with no complications and the children develop normally.
. The pregnancy loss rate in pregnancies with confined placental mosaicism, diagnosed
by chorionic villus sampling, is higher than among pregnancies without placental
mosaicism.
. Sometimes the presence of significant numbers of abnormal cells in the placenta
interferes with proper placental function. An impaired placenta cannot support the
pregnancy and this may lead to the loss of a chromosomally normal baby.
.The most frequently seen trisomic cells in confined placental mosaicism involve
chromosomes 2, 3, 7, 8 and 16. The next frequently involved are 9, 13, 15, 18, 20 and 22.
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13. CONDITIONS CAUSED BY MOSAICISM:
DOWN SYNDROME- THERE ARE 3 TYPES OF CHROMOSOMAL PATTERN THAT
RESULTS IN OCCURING DOWN SYNDROME. THEY ARE THE TRISOMY 21,
MOSAICISM AND TRANSLOCATION.
MOSAICISM IS THE LEAST COMMON TYPE OF DOWN SYNDROME WHERE THERE
IS AN EXTRA CHROMOSOME IN SOME BUT NOT ALL OF THE CELLS.
PALLISTEN-KILLIAN MOSAIC SYNDROME- A DEVELOPMENTAL DISORDER THAT
CAUSES WEAK MUSCLES, INTELLECTUAL DISABILITY AND OTHER BIRTH DEFFECTS.
KLINEFELTER SYNDROME- THERE IS LOW AMOUNTS OF TESTOSTERONE, WHICH
LEADS TO PROBLEM WITH SEXUAL DEVELOPMENT AND OTHER TISSUES.
ICHTHYOSIS WITH CONFETTI- DISORDER OF SKIN, THAT LEADS TO RED SCALY SKIN
ALL OVER THE BODY.
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14. THANK YOU
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