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LECTURE Klinefelter,Turner & Down Syndrome Muhammad Faiyaz-Ul-Haque, M.Phil, PhD, FRCPath.

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Presentation on theme: "LECTURE Klinefelter,Turner & Down Syndrome Muhammad Faiyaz-Ul-Haque, M.Phil, PhD, FRCPath."— Presentation transcript:

1 LECTURE Klinefelter,Turner & Down Syndrome Muhammad Faiyaz-Ul-Haque, M.Phil, PhD, FRCPath

2 Lecture Objectives: By the end of this lecture, the students should be able to: Define non-disjunction and describe its consequences for meiosis and mitosis. Classify chromosomal abnormalities Understand the common numerical chromosomal disorders: mono and trisomy Understand the common numerical sex chromosome disorders: Turner`s & Klinefelter`s syndromes

3 Stages of Mitosis & Meiosis Mitosis Meiosis

4 Stages of Meiosis

5 Non-disjunction in Meiosis  Nondisjunction ("not coming apart") is the failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2.  Can affect each pair of chromosomes  Is not a rare event  As a result, one daughter cell has two chromosomes or two chromatids, and the other has none.  The result of this error is a cell with an imbalance of chromosomes (Aneuploidy)

6 MEIOSIS MITOSIS

7

8 Down Syndrome

9  Three copies of chromosome 21 Down’s Syndrome

10 Down syndrome, trisomy 21 Karyotype: 47, XY, +21 The incidence of trisomy 21 rises sharply with increasing maternal age Most cases arise from non disjunction in the first meiotic division The father contributing the extra chromosome in 15% of cases (i.e. Down syndrome can also be the result of nondisjunction of the father's chromosome 21) A small proportion of cases are mosaic and these probably arise from a non disjunction event in an early zygotic division

11  Short, broad hands  Stubby fingers  Rough skin  Impotency in males  Mentally retarded  Small round face  Protruding tongue  Short lifespan  Short, broad hands  Stubby fingers  Rough skin  Impotency in males  Mentally retarded  Small round face  Protruding tongue  Short lifespan Down Syndrome

12 Low muscle tone Head and facial malformations Abnormalities of the extremities Developmental delays Heart malformations Increased risk of infectious disease Early death Features of Down Syndrome

13 Down Syndrome

14 Turner’s Syndrome

15 Monosomy of sex chromosome (only one X chromosome present) Occurrence – 1 in 2500 live female births Turner Syndrome

16  Monosomy of sex chromosome (only one X chromosome present)  Occurring in 1 in 2500 phenotypic females  The only viable monosomy in humans  Characteristics: Webbed neck, Individuals are genetically female, not mature sexually, Sterile, Short stature, Broad chest, Low hairline, Streak ovaries, Normal intelligence, Normal life span  Monosomy of sex chromosome (only one X chromosome present)  Occurring in 1 in 2500 phenotypic females  The only viable monosomy in humans  Characteristics: Webbed neck, Individuals are genetically female, not mature sexually, Sterile, Short stature, Broad chest, Low hairline, Streak ovaries, Normal intelligence, Normal life span Turner’s syndrome (Monosomy X: 45, XO) Turner’s syndrome (Monosomy X: 45, XO)

17 Short stature Lack of ovarian development Neck abnormalities Skeletal disorders Increased risk of osteoporosis, cardiovascular constriction, diabetes, and kidney and thyroid problems No developmental delays Turner syndrome is commonly treated with growth hormones, and estrogen replacement therapy. Additionally, reproductive technology can help women with Turner syndrome become pregnant. Features of Turner Syndrome

18 Turner Syndrome (XO), Incidence: 1 in 2500 female births XO – Turner Syndrome 96-98% do not survive to birth

19 Cardiovascular Bicuspid aortic valve Coarctation of the aorta Thoracic aortic aneurysmThoracic aortic aneurysm (aortic root dilatation) Skeletal Short stature Short fourth metacarpal/matatarsal bone may be unusually short (+/- short 3rd and 5th). OsteoporosisOsteoporosis (due to lack of estrogen) Scoliosis Reproductive Women with Turner syndrome are almost universally infertile.infertile Cardiovascular Bicuspid aortic valve Coarctation of the aorta Thoracic aortic aneurysmThoracic aortic aneurysm (aortic root dilatation) Skeletal Short stature Short fourth metacarpal/matatarsal bone may be unusually short (+/- short 3rd and 5th). OsteoporosisOsteoporosis (due to lack of estrogen) Scoliosis Reproductive Women with Turner syndrome are almost universally infertile.infertile Turner’s Syndrome

20 Klinefelter’s Syndrome

21 1 in 1,100 births 47 chromosomes XXY only 47, XXY #23 Trisomy Nondisjunction Klinefelter’s Syndrome

22 Male sex organs; unusually small testes which fail to produce normal levels of testosterone  breast enlargement (gynaecomastia) and other feminine body characteristic Patients are taller and thinner than average and may have a slight reduction in IQ but generally they have normal intelligence No spermatogenesis  sterile Very rarely more extreme forms of Klinefelter syndrome occur where the patient has 48, XXXY or even 49, XXXXY karyotype. These individuals are generally severely retarded. Klinefelter Syndrome (XXY), Incidence: 1:1000 male births Klinefelter Syndrome: 47,XXY males

23 Scarce beard Longer fingers and arms Sterile Delicate skin Low mental ability Normal lifespan Klinefelter’s Syndrome Brown spots (nevi)

24 Tall, sexually underdeveloped & infertile, though in some case testicular function is preserved Sparse facial and body hair Delays in speech and motor skills as well as deficits in attention, auditory processing and social skills. Increased risk of autoimmune disorders, breast cancer, osteoporosis, leg ulcers, depression, and dental problems Treatment for these problems includes testosterone therapy and assisted learning Features of Klinefelter Syndrome

25 47, XYY May be without any symptoms. Males are tall but normally proportioned points reduction in IQ compared to sibs. XXX females It seems to do little harm, individuals are fertile and do not transmit the extra chromosome. They do have a reduction in IQ comparable to that of Kleinfelter's males Sex chromosome unbalance is much less deleterious Sex chromosome unbalance is much less deleterious

26 Prenatal: maternal age>37yrs; USS changes; Family history Triple test = increased risk Postnatal: Learning & developmental disability; growth retardation Infertility: Recurrent miscarriage, primary infertility When to do a chromosomal test

27 Autosomal: –Trisomy 21 (Down syndrome) Sex chromosome: –47XXY (Klinefelter syndrome) –45X (Turner syndrome) Aneuploidy

28  Aneuploidy refers to a numerical change in part of the chromosome set  Polyploidy refers to a numerical change in the whole set of chromosomes Aneuploidy & Polyploidy:

29 Available on amniocentesis sample Uncultured amniocytes FISH probes for X,Y, 21 Result in hours Proceed onto full karyotype (11-14 days) Rapid Aneuploidy Screening by FISH

30 qf (quantitative) PCR – able to measure number of copies of a chromosome – used for trisomy screening Fetal DNA – at 6-8 weeks to determine sex – look for presence of Y chromosome material New techniques

31 Polyploidy (extra sets of chromosomes) can produce stronger and larger plants. Important crop plants are produced this way, including bananas! Not all chromosomal mutations are harmful. Not all chromosomal mutations are harmful.

32 Chromosome abnormalities can be numerical or structural. Numerical abnormalities include aneuploidy and polyploidy. In mono or trisomy, a single extra chromosome is absent or present, usually as a result of non-disjunction in the 1 st or 2 nd meiotic division. Structural abnormalities include translocations, inversions, deletions, isochromosome & rings. Take home message


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