Structural Abnormalities of Chromosomes Flashcards
Cri-DuChat Syndrome
Deletion of chromosome 5
Haploinsufficiency
Hypertelorism, epicanthal folds
Cat’s cry
DiGeorge Syndrome
Deletion of chromosome 22q11
Haploinsufficiency of TBX1 gene
CATCH-22: Cardiac abnormality, abnormal faces, thymic aplasia, cleft palate, hypocalcemia
Prader-Will Syndrome
Deletion regarding chromosome 15 - fathers
Angelman Syndrome
Deletion regarding chromosome 15 - mothers
Charcot-Marie-Tooth Disease
Duplication of chromosome 17p12
Leads to increased dosage of PMP22 (peripheral myelin 22)
Which causes demyelinating peripheral neuropathy
Can cause hereditary neuropathy with liability to pressure palsies (HNLPP)
What are inversions?
The result of 2 breaks on a chromosome
Paracentric inversion?
Doesn’t involve centromere (both breaks in one arm), hard to recognize
Pericentric inversion?
Involves centromere (breaks involve both arms), easier to recognize
May lead to unbalanced gametes with ether duplication or deletion of genetic material
What are ring chromosomes?
Deletion occurs at both tips of the chromosome, resulting new ends then u se to for a ring; often results in turner syndrome (45, X), females
Isochromosomes?
Chromosome divides along the axis perpendicularly to usual axis of division; arises from abnormal centromere division
Results in a chromosome with 2 copies of 1 arm and no copies of the other, seen in Turner Syndrome, denoted, in this isochrome case as: 46, X, i (Xq)
Insertions?
Rare type of translocation
Reciprocal translocation
1 in 600 newborns
breakage of NON-homologous chromosomes and reciprocal exchange of resulting segments
e.g. Philodelphia chromosome: reciprocal translocatio involving chr 9 and 22 to forming der 9 and der 22 (Associated to chronic myelogenous leukemia)
Robertsonian translocation
Confined to acrocentric chromosomes (13, 14, 15, 21, 22)
14 and 21, accounts for ~4% of Down syndrome
