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Genetic disorders


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Genetic disorders

  1. 1. Genetic Disorders
  2. 2.  Congenital disorders caused by one or more abnormalities in the genome  Important cause of MR  Higher frequencies among spontaneous abortions and stillbirths  abN. Of chromosomes and numbers
  3. 3. Causes  Due to imbalance of genetic information  Heredity (altered chromosome is passed from parent to child )  New mutations or changes of the DNA  The abnormality happens when either the sperm or egg (germ cells) is created  Soon after conception.
  4. 4. Changes in number of chromosomes Most people have 23 pairs of chromosomes, or 46 chromosomes in all. When the egg or sperm is made, the pairs split so that each egg or germ cell only contains 23 chromosomes. . Changes in chromosome structure Sometimes the information contained in a chromosome breaks up and the pieces reform in a different pattern. For example, a fragment of chromosome may break off and be lost during the formation of either the egg or sperm cell. A section of chromosome might also break away and ‘stick’ to another chromosome. Uniparental disomy Uniparental disomy means the child inherited a particular gene pair (both copies of the gene) from one parent only. This can cause a disorder if it is necessary for the child to have inherited one such gene from each parent.
  5. 5. Chromosomal mosaicism Normally every cell in the body contains the same genetic information – all 46 chromosomes, designated as 46XX (female) or 46XY (male). A person who has chromosomal mosaicism has different numbers of chromosomes in different cells; for example, 46 in some cells and 47 in others. Mitochondrial disorders Mitochondria are like little batteries that make energy within each cell. The energy source is a chemical called adenosine triphosphate (ATP). Organs like the brain, heart and liver can’t survive without ATP. Multifactorial disorders Multifactorial (involving several factors) disorders, such as many common birth defects or diseases like high blood pressure, are disorders caused by the environment interacting with the action of several genes. (This is also sometimes called polygenic inheritance.) For example, the birth defect spina bifida is caused by the action of several genes and also depends on the amount of folate in the mother’s diet during pregnancy (the environment). High blood pressure is influenced by a large number of genes, but also is influenced by a person's diet and salt intake.
  6. 6. Patau’s Syndrome (Trisomy 13) • • • • • • • • • • • • Epidemiology: Cleft lip often midline flexed fingers with polydactyly ocular hypertelorism bulbous nose low-set malformed ears small abnormal skull cerebral malformation, especially holoprosencephaly Micropthalmia cardiac malformations scalp defects hypoplastic or absent ribs visceral and genital anomalies 1/10,000 at risk with pregnancy of 31 years and above
  7. 7. Edward’s Syndrome (Trisomy 18) Many affected infants do not survive before birth Apnea: may cause death Med lifespan: 5-15 days ab • Low birth weight • closed fist with index finger overlapping the third digit and the fifth digit overlapping the fourth • narrow hips with limited abduction • short sternum • rocker-bottom feet • Microcephaly • prominent occiput • Micrognathia • cardiac and renal malformations • MR
  8. 8. Down Syndrome (Trisomy 21) • • • • • • Hypotonia • flat face; upward and slanted palpebral fissures and epicanthic folds • speckled irises (Brushfield Spots) • varying decrease of mental and growth retardation • dysplasia of the pelvis • cardiac malformations and simian creases • short, broad hands • hypoplasia of the middle phalanx of 5th finger • intestinal atresia • high arched palate Lifespan: up to 50y/o (only trisomy compatible with life MC IQ: 30-50 Usually from mother’s egg (at risk with pregnancy of 35 years and above)
  9. 9. Mosaicism (Trisomy 8) Long face high prominent forehead wide upturned nose thick everted lower lip Microretrognathia low-set ears high arched, sometimes cleft palate • Osteoarticular anomalies are common, moderate MR • • • • • • •
  10. 10. Mosaicism   Term used to describe an individual who has two different cell lines derived from a single zygote a condition in which cells within the same person have a different genetic makeup. This condition can affect any type of cell, including:      Blood cells Egg and sperm cells (gametes) Skin cells caused by an error in cell division very early in the development of the unborn baby Less severe
  11. 11. Kllinefelter’s Syndrome  Extra ‘x’ chromosome  Affects 1-2/1,000 males  Males are affected  Mentally disadvantage, sterile male with underdeveloped testes, broader hips, scant body hair, and enlarged breasts
  12. 12. Turner’s Syndrome     One of the MC monosmies Loss of part or all of one of the sex chromosomes 1 /4000 liveborn females or 1/8000 5-10% have some Y chromosome material in all or some cells        Short stature Underdeveloped gonads Virtually no ovaries Reproductive sterility Web neck Underdeveloped breasts and widely spaced nipples N intelligence
  13. 13. Chromosomal Deletion  4p- Wolf-Hirschhorn syndrome  5p- Cri-du-chat Syndrome  9p 13p 18p 21p-
  14. 14. Chromosomal Deletions          7p11.23 8q24.1 11p13 15q11-13 15q11-13(mat) 16p13-17p11.2 17p13.3 20p12 22q11.2 Williams Langer-Giedion or trichorhino-phalangeal, type II WAGR Prader- Willi Angelman Rubinstein Taybi SmithMagenis Miller-Dieker Alagille syndrome Velocardiofacial-DiGeorge syndrome