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Chromosomal anomalies

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Genetics

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Chromosomal anomalies

  1. 1. By : Gan Quan Fu, PT, MSc Human Anatomy (Batch 3)
  2. 2.  Introduction  Classification of Genetic Disorder  Definition & Prevalence  Autosomal Anomalies  Numeric Chromosomal Anomalies  Structural Chromosomal Anomalies  Sex Chromosome Anomalies  Numeric Chromosomal Anomalies  Structural Chromosomal Anomalies  Important definitions in Genetics
  3. 3. Classification of Genetic Disorder Single gene disorders Chromosomal Disorder Autosomal Numeric Structural Sex Chromosome Numeric Structural Multifactorial Disorder Acquired Somatic Genetic Disease
  4. 4.  Chromosomal Anomalies = Missing, extra, or irregular portion of chromosomal DNA.  Most foetus with some chromosomal abnormality do not survive.  Affects approximately 1 out of 200 of new- borns.  Karyotype = Full set of chromosomes from an individual. (Chromosomal Anomalies can be detected via Karyotype Testing.)  Abnormalities depends on type of chromosome affected due to non-disjunction chromosomes.
  5. 5. Chromosome affected Autosomes Numeric Autosomal Trisomies Autosomal Monosomy Structural Single Chromosome Disorder Two Chromosome Disorder Sex Chromosomes Numeric Structural
  6. 6. Monosomy Trisomies
  7. 7. Autosomal Anomalies (Numeric) Monosomy Single copy of an autosome. Lethal in early pregnancy. Trisomies Patau Syndrome (47 + 13) Edwards Syndrome (47 + 18) Down Syndrome (47 + 21)
  8. 8.  An additional chromosome 13 resulting from nondisjunction during meiosis.  Incidence = 1 in 10,000 -20,000 live births.  More than 80% die within the first year of life.  Anomalies can be seen on:  Nervous & Optic System  Musculoskeletal & Cutaneous  Urogenital & Cardiovascular System
  9. 9.  Intellectual disability and motor disorder  Microcephaly  Holoprosencephaly (failure of the forebrain to divide properly).  Structural eye defect:  Microphthalmia  Peters anomaly (a type of eye abnormality)  Cataract  Iris and/or fundus (coloboma)  Retinal dysplasia or retinal detachment  Sensory nystagmus  Cortical visual loss  Optic nerve hypoplasia  Meningomyelocele (a spinal defect)
  10. 10.  Polydactyly (extra digits)  Cyclopia  Proboscis  Congenital trigger digits  Low-set ears  Prominent heel  Deformed feet known as rocker-bottom feet  Omphalocele (abdominal defect)  Abnormal palm pattern  Overlapping of fingers over thumb  Cutis aplasia (missing portion of the skin/hair)  Cleft palate
  11. 11.  Urogenital  Abnormal genitalia  Kidney defects  Cardiovascular  Heart defects (ventricular septal defect & Patent Ductus Arteriosus)  Dextrocardia  Single umbilical artery
  12. 12. A. Midline defect with cleft lip & palate. B. Clenched hand with overlapping fingers. C. Postaxial polydactyly. D.Equinovarus deformity. E. Punched out aplasia cutis scalp lesions.
  13. 13.  An additional chromosome 18 resulting from nondisjunction during meiosis.  Incidence =1 in 6000 - 8000 live birth.  Majority of fetuses with this syndrome die before birth; >90% dead in 1st year.  80% affected were females.
  14. 14.  Kidney malformations  Structural heart defects at birth  Ventricular septal defect  Atrial septal defect  Patent ductus arteriosus  Omphalocele (Intestines protruding outside the body)  Esophageal atresia  Intellectual disability  Developmental delays  Growth deficiency  Feeding difficulties  Breathing difficulties  Arthrogryposis (a muscle disorder that causes multiple joint contractures at birth)
  15. 15.  Small head (microcephaly) accompanied by a prominent back portion of the head (occiput),  Low-set, malformed ears,  Abnormally small jaw (micrognathia),  Cleft lip/cleft palate,  Upturned nose,  Narrow eyelid folds (palpebral fissures),  Widely spaced eyes (ocular hypertelorism),  Drooping of the upper eyelids (ptosis),  A short breast bone,  Clenched hands  Choroid plexus cysts  Underdeveloped thumbs and/or nails  Absent radius  Webbing of the second and third toes, clubfoot or rocker bottom feet  Males will have undescended testicles.
  16. 16.  An additional chromosome 21 resulting from nondisjunction during meiosis. (*Extra chromosome 21 in every cell of the body)  John Langdon Down (the British physician) who described the syndrome in 1866.  Karyotype = 47,XX+21 or 47,XY+21
  17. 17. Characteristics Percentage Characteristics Percentage Mental impairment 99% Abnormal teeth 60% Stunted growth 90% Slanted eyes 60% Umbilical hernia 90% Shortened hands 60% Increased skin back of neck 80% Short neck 60% Low muscle tone 80% Obstructive sleep apnea 60% Narrow roof of mouth 76% Bent fifth finger tip 57% Flat head 75% Brushfield spots in the iris 56% Flexible ligaments 75% Single transverse palmar crease 53% Large tongue 75% Protruding tongue 47% Abnormal outer ears 70% Congenital heart disease 40% Flattened nose 68% Strabismus ~35% Separation of first and second toes 68% Undescended testicles 20%
  18. 18.  Can happen in a chromosome itself, the other is not required. Deletion (Genetic material missing) Duplication (Genetic material present twice) Inversion (Genetic material is “flipped”)
  19. 19.  Need 2 chromosomes to occur these processes. Insertion (Genetic material is added from another chromosome) Translocation (Material is swapped(exchanged) with another chromosome)
  20. 20.  Name is based on the infant’s cry. (high- pitched and sounds like a cat.)  Incidence =1 in 216,000 birth  Normal 46 chromosomes but, missing a piece of chromosome number 5.  Most cases are believed to occur during the development of the egg or sperm, small number of cases occur when a parent passes a different, rearranged form of the chromosome to their child.
  21. 21.  Cry is high pitched and similar to that of a meowing kitten.  Moon-shaped face  Malformed larynx  Difficulty swallowing and sucking (Feeding Problem).  Low birth weight and poor growth.  Severe cognitive, speech, and motor delays, mental retardation  Behavioural problems such as hyperactivity, aggression, and repetitive movements.  Excessive drooling(ptyalism)
  22. 22. Chromosome affected Autosomes Numeric Structural Sex Chromosomes Numeric Autosomal Trisomies Autosomal Monosomy Structural X-link Dorminant X-link Recessive
  23. 23. Sex Chromosome Anomalies (Numeric) Monosomy Turner’s syndrome (45,X0) Trisomies Klinefelter's syndrome (47,XXY) Jacob’s syndrome (47,XYY) Triple x syndrome (47,XXX)
  24. 24.  Sex chromosomal monosomy(45, XO)  99% of foetuses with Turner syndrome result in spontaneous termination during the first trimester.  Incidence = 1 in 2000-5000.
  25. 25.  Short stature  Skeletal disorders (osteoporosis which may lead to scoliosis)  Webbed neck(due to cystic hygroma)  Broad shoulders  Broad chest (shield chest), widely spaced nipples  No/Poor breast development  Narrow hips (High waist-to-hip ratio: hips are not much bigger than waist)  Lymphedema of hands and feet  Shortened metacarpal IV  Cubitus valgus
  26. 26.  Underdeveloped ovaries(streak gonads, hence this syndrome also called ovarian dysgenesis)  Sterile, lack expected secondary sex characteristics  Amenorrhoea(No menstruation)  Cardiovascular problems (Coarctation of the aorta, Bicuspid aortic valve)  Horse shoe kidney  Thyroid problems (hypothyroidism specifically Hashimoto's thyroiditis).
  27. 27.  XXY Males  Disorder occurring due to nondisjunction of the X chromosome during Meiosis.  Extra X chromosome is nondisjunction during meiosis II of the germ cell in the female.  Occur when sister chromatids on the X sex chromosome fail to separate.  XX ovum produced and when fertilized with a Y- sperm it yields XXY offspring. Also occurs X and Y sex chromosomes fail to separate, producing a sperm with an X and Y chromosome & fertilize with normal X ovum produces XXY offspring.  Incidence = 1 in 500 live male births.
  28. 28.  48, XXYY (male) syndrome  Incidence = 1 in 18,000–40,000 births  48,XXXY  Incidence = Extremely rare
  29. 29.  Childhood  Weaker muscles and reduced strength.  Puberty (features become more prominent due to hypogonadism (less amount of testosterone produced):  Rounded body type  Broader hips  Little body hair is present  Gynecomastia (increased breast tissue)  Microorchidism (i.e. small testicles)  Azospermia leading to infertility  Micropenis  Tall stature  IQ is normal
  30. 30.  Characterized by the presence of an additional Y chromosome.  Incidence = 1 in 1,800 births  Features Present:  Normal physically  Normal mentally  Increase in testosterone  More aggressive  Normal lifespan  There are article which claims that those with Jacob’s Syndrome are more prone in committing crime.
  31. 31.  Characterized by the presence of an additional X chromosome.  When an XX ovum fertilizes with X- sperm.  Incidence = 1 in 1,000 birth  Features Present  Normal physically, Sometimes taller.  Normal mentally, Increase risk of retardation and learning difficulties.  Fertile.
  32. 32. Genotype Gender Syndrome Physical Traits XY Male - XXY XXYY XXXY Male Klinefelter’s Syndrome sterility, small testicles, breast enlargement XYY Male XYY or Jacob’s Syndrome normal male traits XX Female - XO Female Turner Syndrome sex organs don’t mature at adolescence, sterility, short stature XXX Female Triple X tall stature, learning disabilities, limited fertility
  33. 33. Sex Chromosome Anomalies (Structural) Y-Linked Disease Very Rare X-Linked Disease X-Linked Dominant X-Linked Recessive
  34. 34.  Also known as ‘holandric inheritance’.  Determination of a phenotypic trait by an allele (or gene) on the Y chromosome.  Pass from father to son with no interchromosomal genetic recombination  Very rare.  Deletion (missing genetic materials) in Y- gene is a frequent genetic cause of male infertility.  Having hairy ears was once thought to be a Y-linked trait in humans, but that hypothesis has been discredited.
  35. 35.  Single gene disorders that reflect the presence of defective genes on the X chromosome.  Show inheritance patterns that differ from autosomal diseases.  Male have one X chromosome + a Y chromosome while females have 2 X chromosome, they show different patterns of inheritance and severity of manifestation. (There are both dominant and recessive X-linked diseases, also there are some characteristics that are common to X-linked disorders in general).  Males are never carriers, if they have a mutated gene on the X chromosome, it will be expressed.  Males are termed hemizygous for genes on the X chromosome.
  36. 36.  Expressed in females when only a single copy of the mutated gene is present.  Very few diseases have been identified:  Alport syndrome  Nephrogenic Diabetes Insipidus  Hypophosphatemic rickets or vitamin D resistant rickets (leading to low serum phosphorus & skeletal abnormalities)  Never passed from father to son.  Affected males produce only affected females. (An affected male only has one X chromosome to pass on to his daughters.  Affected females produces 50% normal and 50% affected offspring. (Heterozygous).  Males are usually more severely affected than females. Some X- linked traits may even be lethal.  Females are more likely affected. (They have 2x increase risk to inherit the mutated allele, since they have 2X chromosomes)
  37. 37.  Inherited, heterogeneous disorders involving basement membranes of kidney, frequently affecting the cochlea and eyes.  Clinical Manifestation:  Renal  Hematuria  Proteinuria  Hypertension with edema and nephrotic syndrome at later stage.  Hearing  Sensorineural deafness (90% are deaf by age of 40 years)  Ocular  Dot-and-fleck retinopathy  Leiomyomatosis  Diffuse leiomyomatosis of the esophagus and tracheobronchial tree
  38. 38.  Occurs when the kidneys cannot concentrate urine normally resulting excretion of large amount of dilute urine. *Kidney tubules do not respond to Antidiuretic Hormone (ADH).  Very Rare  Symptoms  Intense or uncontrollable thirst, and crave ice water.  Produce large amounts of urine (usually more than 3 liters, and up to 15 liters per day.)  Easily dehydrated
  39. 39.  Form of rickets characterized by low serum phosphate levels.  Resistance to treatment with ultraviolet radiation or vitamin D ingestion.  Incidence = 1 in 20,000 newborns  Symptoms:  Short stature  Associated with this condition is disproportionate, resulting from deformity and growth retardation of the lower extremities.  Bow Legged and deformities associated with bones  Bone Pain and Joint Pain
  40. 40.  Hereditary pattern which a recessive gene in X chromosome results in:  Male : Manifestation of characteristics  Female : Carrier (Usually)  Males are more likely affected, they only need one copy of mutant allele to express phenotype.  Female must have 2 copies of the mutant allele in order for the mutant phenotype to develop.  Female with 1 copy of the mutant allele is only a carrier.  Disorders are:  Colour blindness  Duchenne Muscular Dystrophy  Hemophilia
  41. 41.  Also known as colour vision deficiency (CVD).  Trouble seeing  Red  Green  Blue  Mix of colours mentioned above.  Rarely that a person sees no color at all.  Three types of cone cells in eye (each type senses either red, green, or blue light most concentrated in macula). Individuals with colour blindness do not have these cone cells.  Incidence = Approximately 1 in 12 men (8%); 1 in 200 women
  42. 42.  Form of muscular dystrophy (muscle weakness and loss of muscle tissues) which worsens quickly.  Caused by a defective gene for dystrophin (A type of protein in muscles).  Incidence = 1 in 3,600 male infants
  43. 43.  Usually appear before age 6 and may appear as early as infancy.  Include:  Fatigue  Learning difficulties (IQ can be below 75)  Intellectual disability  Muscle weakness:  Begins in the legs and pelvis less severe in the arms, neck, and other areas of the body  Problems with motor skills (running, hopping, jumping)  Frequent falls  Trouble getting up from a lying position or climbing stairs  Weakness quickly gets worse  Progressive difficulty walking:  Ability to walk may be lost by age 12  Breathing difficulties and heart disease usually start by age 20
  44. 44.  Blood fails to clot normally  Lacking a blood clotting factor VIII (antihemophilic globulin, AHG), IX (Chrismas Factor).  Bleeding from even minor cuts  Incidence = 1,500 newborn males.  Hemophilia A = Lack of clotting factor VIII. 75% occurrence.  Hemophilia B = "Christmas Disease" is a defect in clotting factor IX.  Transfusions of fresh whole blood or plasma or factor to control bleeding
  45. 45.  Also known as Martin-Bell syndrome; Marker X syndrome.  Some consider this syndrome as X-linked dorminant, some consider this as X-linked recessive which some claims this to be not under X-linked dorminant or recessive.  Genetic condition involving changes in the long arm of the X chromosome.  Characterized by mental retardation.  Fragile area on X chromosome tends to repeat bits of the genetic code. (*More repeats, the more likely there is to be a problem.)  Male and female can both be affected.  Male have only one X chromosome, single fragile X more likely to affect them more severely.
  46. 46.  Family history of fragile X syndrome, especially a male relative  Mental retardation  Large testicles (macro-orchidism)  Large size  Tendency to avoid eye contact  Hyperactive behaviour  Large forehead and/or ears with a prominent jaw
  47. 47.  Aneuploidy = Addition or loss of one (rarely two) chromosome.  Trisomy = 3 copies of a chromosome, (2n+1)  Tetrasomy = 4 copies of a chromosome, (2n+2)etc  Monosomy = 1 member of a chromosome pair missing, (2n-1) that is only single copy of a chromosome is present.  Euploidy = Normal condition, where the genotype consists of complete two sets of chromosomes (23+23 or 2n).  Genotype = Genetic make up of cell.  Karyotype = Number and appearance of chromosome in a nucleus.  Non disjunction = Incorrect separation of chromosomes or sister chromatids during meiosis.  Phenotype = Characteristics of an Organism  Polyploidy = Entire extra set of chromosomes present, [can be triploidy(3n= 69 chromosomes),tetraploidy(4n=92 chromosomes) etc.]
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Genetics

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