Chromosomal Abnormalities-Sasi-converted.pdf

Nursing genetics

1. CHROMOSOMAL ABNORMALITIES
Prof.Ms.SasikalavathiArunachalam M.Sc(N) OBG

2. Chromosomes are complex structures located in the cell
nucleus.
They are composed of DNA, histoneand non-histoneproteins,
RNA , and polysaccharides.
They are basically the "packages" that contain the DNA.

4. Normal Karyotype
Karyotype: a picture of the chromosomes from a single cell

5. Human chromosome

6. A group——1～3
B group——4～5
C group——6～12 +X
D group——13～15
E group——16～18
F group——19～20
G group——21～22 +Y
Classification

7. Chromosome abnormality
Numerical abnormality
Structural abnormality
Aneuploidy
Polyploidy
translocation
deletion
insertion
inversion
rings
isochromosome

8. Numerical
Aberrations
Aneuploidy
Hyperploidy
Trisomy
2
n
+1
Tetrasomy2
n
+2
Hypoploidy
Monosomy2
n
-1
Nullisomy
2
n
-2
Euploidy
Monoploidyn
Diploidy2n
Polyploidy 3n

11. Non-disjunction In meiosis

12. Aneuploidy
Down’s
Syndrome
(Trisomy21)
Edward’s
Syndrome
( Trisomy18)
Patau
Syndrome
(Trisomy13)

13. Down’s
Syndrome
Non-
disjunction
During Mitosis

14. Down’s syndrome
First identified by Dr Langdon Down in 1866
Trisomy21
1in 700 live births
Associated with increased maternal age
Newborn –Hypotonia, increased sleepiness , excess
nuchalskin
Mental retardation
Small stature
Craniofacial findings –brachycephaly( flat occiput) ,
epicanthic folds , upward slanting eyes , protruding
tongue, low set ears , flat nose , low nasal bridge , high
arched palate

15. Short broad hands
Clinodactyly( incurving ) little finger
ASD,VSD , PDA
Anal duodenal atresia
Happy & affectionate

16. Edward’s syndrome
Trisomy18
Described by Edward in 1960
Incidence 1/8000
Rare to find live born
>90% dead in 1
st
year
Do not live beyond few months
Features –mental retardation , failure to thrive ,
hypotonia, prominent occiput, low set ears , receding
jaw , short sternum , clenched fists, rocker bottom feet.
➢VSD and horseshoe kidney

18. Patau’ssyndrome
Trisomy13
Die in a month
Growth & mental retardation
Sloping forehead , hypertelorism, microphthalmia
, cleft lip , cleft palate , polydactyly, polycystic
kidneys , bicornuateuterus

21. Turner syndrome
➢Complete or partial monosomy of X chromosome
➢Hypogonadism in phenotypic females
➢1 in 2000 live born females
➢57% missing an entire X chromosome-45, X karyotype
➢14% have structural abnormalities of X chromosome
➢29% are mosaics
➢Structural abnormalitiesare-
❖Deletion of small arm-iso chromosome of long arm-46,X,i(X)(q10)
❖Deletion of portion of both long and short arms-ring chromosome-46,X,r,(X)
❖Deletion of portion of short or long arm-46X,del (Xq)
➢Mosaic patterns-
❖45,X/47XXX

22. ➢Female, short stature, primary amenorrhea, sterility,
spares hair and underdeveloped breast
➢Neonatal: wide spaced nipple, lymphedema , shield chest,

25. Klinefelter syndrome
➢Male hypogonadism occur when there are 2 /more X chromosome
and one /more Y chromosome.
➢1 in 660 live male births
➢Eunuchoid body habitus (tall, slim and underweight with abnormally
long legs & long arms), small atrpohic testis, lack of secondary male
characteristics.
➢Increased incidence of type 2 diabetes, metabolic syndrome
➢Higher risk of breast cancer, extragonadal germ cell tumor and
autoimmune diseases
➢47,XXY-90% cases, 15% cases are mosaics

27. Polyploidy
More than two sets of chromosomes per nucleus.
23 chromosomes = one set of chromosomes.
69,XXY 92,XXXY

28. Diandry Digyny

29. Deletion-loss of a portion of chromosome
STRUCTURAL ABNORMALITIES

31. Cri du chat means cat cry in french
Deletion (the length of which may vary) on the short arm of chromosome
5.
Jerome Lejeune 1963 (French Genitist)
The baby is small at birth, may have respiratory problems , the larynx
doesn't develop correctly, which causes the cat-like cry.
Microcephaly, an unusually round face, a small chin, widely set eyes,
folds of skin over their eyes, and a small bridge of the nose.
Cri-du-Chat Syndrome

32. Small head
(microcephally)
Low setear
Widely spaced eyes
(hypertelorism) Low
broad nasalridge
Small receding
chin(micrognathia)

33. RING CHROMOSOME

34. Insertion

35. Inversion-2 breaks, turns upside down and re-attaches

36. Isochromosome-one arm is lost, other arm is reduplicated

37. Translocation-one segment transferred to another.