CHROMOSOMAL ABBERATIONS Flashcards
WEEK 16
Chromosomal aberration etiology:
If there is an error in cell division, the egg or sperm can end up with too many or not enough chromosomes.
Meiosis
Chromosomal aberration etiology:
If the chromosome does not split into halves, the new cells can have an extra chromosome or have a missing chromosome
Mitosis
Chromosomal aberration etiology:
Eggs are also aging and may have the incorrect number of chromosomes at the time of fertilization
Maternal age
Chromosomal aberration etiology:
it describes a relationship between two people who share a common ancestor or shared a blood relationship
Consanguinity
Chromosomal aberration etiology:
it is a teratogenic
Radiations
Chromosomal aberration etiology:
it may include medications, foods, etc.
Environment
Structural chromosomal aberration:
~It means of loss of small portion of chromosome
~occurs from breakage at random in both chromatids of a chromosome or only in one chromatid
~irreversibly abnormality
Deletion (Deletion of D gene)
Structural chromosomal aberration:
~Sometimes a segment of a chromosome becomes detached and unites with another non-homologous chromosome.
~it is of two types: Simple translocation and Reciprocal translocation
Translocation
Structural chromosomal aberration:
~A fragment is transferred from a chromosome to a non-homologous chromosome
~it is a rare non-reciprocal type of translocation which involves three breaks
Insertion
Structural chromosomal aberration:
~This results in having extra genetic material, even though usually normal
~May cause affected genes to not function properly
~These extra instructions can lead to errors in the development of a baby
(e.g., Malformation)
Duplication
Structural chromosomal aberration:
~it results when there are two breaks in a chromosome and the detached segment becomes reinserted in the reverse order
~it is of two types depending upon inclusion or absence of centromere:
~Paracentric - both breaks in one arm of chromosome (one arm is affected)
~Pericentric - it has breakpoints on either side of the centromere (both arms are affected)
Inversion
Structural chromosomal aberration:
~it is a chromosome that has lost one of its arms and replaced it with an exact copy of the other arm.
Isochromosome
Structural chromosomal aberration:
~it is a chromosome whose arms have fused together to form a ring
Ring Chromosome
Syndromes related to abnormal aberrations:
~also known as ‘Mongolism’ or ‘Mongolian idiocy’
- shows strong mental retardation
~their body is short about 120com with stubby fingers
~Epicanthic fold or Epicanthal fold; prompted Sir John Langdon Haydon Down to term the condition Mongoloid (1866)
~survive about sixteen years
Down Syndrome
Syndromes related to abnormal aberrations:
~happens due to trisomic condition in chromosome no. 13
~the persons suffering from this syndrome show harelip, cleft palate, and serious cerebral, ocular and cardiovascular defects.
~average survival is about three months; a few live up to five years.
~1-3 mos. of life expectancy
Patau Syndrome (Trisomy 13)
Syndromes related to abnormal aberrations:
~The syndrome is characterized by mental deficiency; multiple congenital malformations affect virtually every organ system.
~Great physical and mental abilities (6-month level)
~ “Rocker-bottom feet”
~ Absent/Unusual fingerprints
Edward’s Syndrome (Trisomy 18)
Syndromes related to abnormal aberrations:
~Male aneuploidy
~XXY karyotype
~Gynecomastia; due to high production of estrogen
~Testicular atrophy
~Formation of barr bodies
~Reduced fertility
~Hypogonadism
Klinefelter’s Syndrome
Syndromes related to abnormal aberrations:
~Female aneuploidy
~happens due to monosomy for X-chromosome i.e. the individuals possess one normal X, while the short arm of the other X is missing.
~Virtually no ovaries
~shield like chest
~No mental retardation
~No presence of Barr body
Turner Syndrome/Ulrich-Turner Syndrome/Gonadal dysgenesis (X0)
Turner Syndrome is named after
Henry Turner (1938)
Syndromes related to abnormal aberrations:
~Female aneuploidy
~XXX Karyotype
~Symptoms
~Tall stature
~Microcephaly
~Vertical skinfolds that may cover the inner corners of the eyes (epicanthal folds)
~Delayed development of certain motor skills, speech and language
~Learning disabilities such as dyslexia or weak muscle tone
Triple X/Trisomy X
Syndromes related to abnormal aberrations:
~Male aneuploidy
~XYY Karyotype
~Affected males are apparently normal
~Symptoms:
~Great height, acne, speech and reading problems
Jacob Syndrome
Some disorders arise from loss of just a piece of one chromosome:
~UBE3A gene
~ 50% of cases have a segment of the long arm of chromosome 15 missing, a deletion of the maternal genes, example of imprinting disorder
Symptoms:
~Severe mental retardation
~Hyperactivity
~Ataxia
~Paroxysms of laughter
~Almost-absent speech
Angelman Syndrome
Some disorders arise from loss of just a piece of one chromosome:
~SNRPN gene
~50% of cases have a segment of the long arm of chromosome 15 missing, a deletion of the paternal genes, example of imprinting disorder
Symptoms:
~Mild or moderate mental retardation
~Feeding problems
~Neonatal and infantile hypotonia
~Hyperphagia
~Obesity
~Behavioral problems
Paternal-Willi Syndrome
Some disorders arise from loss of just a piece of one chromosome:
~involves a deletion on the short arm of chromosome 5.
~written as 46, XX, 5p; the critical region for this syndrome is deletion of 15.2
~French term for cat-cry or call of the cat referring to the characteristic cat-like cry of affected children.
~First described by Jerome Lejeune in 1963
~Female individuals are mostly affected
Cri du chat
Some disorders arise from loss of just a piece of one chromosome:
~also known as monosomy 1p36
~is a congenital genetic disorder characterized by:
~moderate to severe intellectual disability
~delayed growth
~hypotonia
~seizures
~limited speech ability
~malformations
~hearing and vision impairment
~distinct facial features
~ONE OF THE MOST COMMON DELETION SYNDROMES
1p36 Deletion Syndrome
Chromosomal abnormalities in cancer cells:
~a translocation mutation commonly associated with chronic myelogenous leukemia and less often with acute lymphoblastic leukemia
Philadelphia chromosome
