Chromosomal abnormality

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Chromosomal abnormality

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Chromosomal abnormalities and syndromes: 

Chromosomal abnormalities and syndromes Dr N aresh T Chauhan

Key concept!: 

Key concept! Mechanisms: chromosomal abnormalities Autosomally abnormal syndromes Sex chromosomally abnormal syndromes Rare but interesting syndromes 2

Introduction: 

Introduction Normal human cells contain 23 pairs of chromosomes This includes one pair of sex chromosome XX or XY During cell division we can identify chromosomes Haploid: set of 23 chromosomes Diploid: normal number of 46 chromosomes 3

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Genetic disorders arise from either structural or numerical change in the chromosome(s) or gene(s) of autosomes or sex chromosomes 4

Structural Chromosomal abnormalities : 

Structural Chromosomal abnormalities Deletion Inversion Translocation Duplication Transverse centromeric division Numerical Chromosomal abnormalities Aneuploidy and Polyploidy 5

Chromosomal deletion: 

Chromosomal deletion 6

Chromosomal inversion: 

Chromosomal inversion 7

Balanced translocation : 

Balanced translocation 8

Unbalanced translocation: 

U nbalanced translocation 9

Chromosomal duplication: 

Chromosomal duplication 10

Aneuploid/ polyploid cells arise due to following events: 

Aneuploid/ polyploid cells arise due to following events Nondisjunction Anaphase lag Multiple gametic fertilization 11

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Nondisjunction: 

Nondisjunction 13

Nondisjunction, Anaphase lag, Multiple gametic fertilization: 

Nondisjunction , Anaphase lag, Multiple gametic fertilization 14

Syndromes: 

S yndromes A syndrome represent a pattern of symptoms and signs common to a set of abnormal individuals e.g Autosomally abnormal syndromes Sex chromosomally abnormal syndromes Rare but interesting syndromes 15

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Here, chromosome 21 has three chromosomes instead of the usual two. This defect causes a genetic disorder known as Down syndrome. 16

Down Syndrome: 

Down Syndrome Incidence 1/700 2/3 of down fetus spontaneously abort Trisomy 21 in 94% of cases with extra chromosome from mother mostly(95%) Risk correlate with maternal age <25 y/o 1/1600 >40 y/0 1/80 2% are mosaic 17

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Trisomy 18: 

Trisomy 18 Small face with prominant occiput Small sternum and pelvis Flexion deformity of the finger VSD and horseshoe kidney 19

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Klinefleter’s 21

Turner’s Syndrome: 

Turner’s Syndrome 22

Turner’s: 

Turner’s Turner syndrome is associated with underdeveloped ovaries, short stature, webbed, and is only in women. Bull neck, and broad chest. Individuals are sterile, and lack expected secondary sexual characteristics. Mental retardation typically not evident. Chromosomal or monogenic? 23

Sickle Cell Anemia: 

Sickle Cell Anemia An inherited, chronic disease in which the red blood cells, normally disc-shaped, become crescent shaped. As a result, they function abnormally and cause small blood clots. These clots give rise to recurrent painful episodes called "sickle cell pain crises". 24

Cystic Fibrosis (CF): 

Cystic Fibrosis (CF) Monogenic Cause: deletion of only 3 bases on chromosome 7 Fluid in lungs, potential respiratory failure Common among Caucasians…1 in 20 are carriers 25

Tay-Sachs disease: 

Tay-Sachs disease Monogenic, autosomal recessive Central nervous system degrades, ultimately causing death. Most common among people of Jewish, eastern Europe descent. 26

Muscular Dystrophy: 

Muscular Dystrophy What Is Muscular Dystrophy? Muscular dystrophy is a disease in which the muscles of the body get weaker and weaker and slowly stop working because of a lack of a certain protein (see the relationship to genetics?) Can be passed on by one or both parents, depending on the form of MD 27

Hemophilia, the royal disease: 

Hemophilia, the royal disease Hemophilia is the oldest known hereditary bleeding disorder. Caused by a recessive gene on the X chromosome. There are about 20,000 hemophilia patients in the United States. One can bleed to death with small cuts. The severity of hemophilia is related to the amount of the clotting factor in the blood. About 70% of hemophilia patients have less than one percent of the normal amount and, thus, have severe hemophilia. 28

X-linked Inheritance pedigree chart: 

X-linked Inheritance pedigree chart 29

Diabetes : 

Diabetes Disease in which the body does not produce or properly use insulin. Insulin is a hormone that is needed to convert sugar, starches, and other food into energy needed for daily life. Genetic mutation can lead to Type 1 diabetes, but no one sure if relative to a specific gene 30

PKU: 

PKU Phenylalanine is an essential amino acid and is found in nearly all foods which contain protein, dairy products, nuts, beans, tofu… etc. A low protein diet must be followed. Brain damage can result if the diet is not followed causing mental retardation…and mousy body odor ( phenylacetic acid is in sweat). 31

Color Blindness: 

Color Blindness Cause: x-linked recessive 1/10 males have, 1/100 females have. Why the difference? Individuals are unable to distinguish shades of red-green. Are you color blind? 32

Albinism: 

Albinism Patients are unable to produce skin or eye pigments, and thus are light-sensitive Autosomal recessive Therefore, is it monogenic or chromosomal? 33

Incidence : 

Incidence The earlier the abortion the more likely to be chromosomal 50% of spontanous abortion are chromosomal abnormal Mostly triploidy . 45 XO, trisomy 16 98% of fetus with turner abort Generally 6/1000 the incidence of chromosomal abnormalities 34

When to suspect it: 

When to suspect it Unexplained infertility Multiple abortion >2 Prior case of defective baby Presence of congenital anomalies 45% have minor single anomalies 9% 3 minor anomalies 1.5% HAVE major anomaly 2 or more major anomalies may represent genetic syndrome or chromosomal abnormalities(10%). 35

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Couples who are at risk for having a child with a genetic disorder can benefit from genetic counseling. The risk is considered high if genetic disorders have occurred in either the man's or the woman's family, if the couple are blood relatives, or if either of them belongs to a high-risk population 36

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Some developmental disorders can be diagnosed with ultrasound in early pregnancy Others can be detected by taking a sample of the amniotic fluid that surrounds the fetus in a procedure called amniocentesis or by taking a sample of the early, developing cells of the chorion , part of the placenta, in a procedure called chorionic villus sampling 37

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Prenatal screening is recommended for pregnant women over 35, those who have already had a child with a genetic disorder, or those who have been exposed to radiation or certain drugs early in pregnancy As more genes that cause specific diseases are being isolated, the use of screening tests to identify those people who unknowingly carry defective genes is becoming more widespread 38

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CHROMOSOMAL ABNORMALITIES Numerical Structural Aneuploidy Polyploidy Monosomy Trisomy SYNDROMES Turner Down Edwards Klinefelter Triploidy Tetraploidy Embryo usually aborts Deletion Cri-du-chat Inversion Miscarriages increase Duplication Insertion Translocation Abnormal segregation in carriers of translocation or inversion Gene disruption Leukemia Lymphoma 39

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In the 1860s, Austrian monk Gregor Mendel discovered the basic laws of heredity by experimenting with pea plants . Gregor Mendel 40

References: * Human Genetics book by Pavankumar Dhar * US National library: 

References: * Human Genetics book by Pavankumar Dhar * US National library 41