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Flashcards in Genetic mechanisms in disease Deck (26):
1

Trisomy 21

Downs syndrome

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Trisomy

Extra chromosome. Possible in the smaller chromosomes with no critical genes but not seen in larger ones.

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Monosomy

Only 2 known examples: 1. Monosomy 21 and Monosomy 22

4

Klinefelter syndrome

XXY or XXYY

5

Turner syndrome

Missing a sex chromosome. XO genotype (not possible to be YO)

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Barr body

Inactive X chromosome

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Mosaicism in women

Some cells in the body have one X activated and some have the other

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Microdeletion

Small deletion spanning several genes which can't be seen in a chromosome test

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Microduplication

Small duplication which can't be seen in a chromosome test. Less problematic than deletions.

10

Balanced translocation

No missing, extra genetic material, often doesn't cause disease unless right through important gene

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Unbalanced translocation

Can see missing/extra piece. Like having a deletion or duplication. Can happen in children of parent with balanced translocation.

12

Contiguous gene syndrome

Microdeletion that spans 2 or more genes adjacent to each other

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Routine chromosome tests

Karyotyping or cytogenic analysis. Can detect 1. Monosomy 2. Trisomy 3. Big deletions 4. Duplications 5. Rearrangements

14

Fluorescent in situ hybridization (FISH)

Will detect microdeletions and duplications, but need to know what you are looking for.

15

Subtelomeric FISH

Detects microdeletions and subtle rearrangements that disrupt genes near ends of chromosomes which can cause mental retardation.

16

Microarray (CMA, CGH)

Also called genomic array. First line test used-multiple probes and don't need to know what you're looking for. Results can be known disease (diagnosis), "variant of unknown significance," parents have/don’t have (diagnosis) it, benign normal CNVs (copy normal variants). Used for detecting intellectual deficiencies with unknown cause, multiple congenital anomalies, seizures, microcephaly. Costs $2600

17

Pathogenic CNVs

Usually bigger, deletions/amplifications, genes in CNS

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Benign CNVs

Usually smaller, gene-poor, present in healthy relative, duplications better than deletions

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Risk CNVs

Inherited, variable penetrance but occur in disease state more often than normal, deletions/duplications, genes in CNS. Genetic counseling difficult.

20

Williams syndrome

Neurodevelopmental disorder form deletion in 26 genes on chromosome 7

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Dominant negative effect

When defective protein inhibits function of normal one in dimer/multimer

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Neurophakomatoses

Loss of functionn in tumor suppressor genes-second hit gives cancer

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X-linked lethal

Only females get this X-linked disease because males die before birth

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Exome sequencing (NextGen)

Looks for homozygous rare variants in affected individuals/families with patterns of dominant or recessive disease. Successful, but sometimes find other risk variants.

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Families with recurring recessive disease (inbred)

Homozygosity mapping followed by focused Sanger or focused/whole exome sequencing

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Families with recurring dominant disease

Linkage followed by Sanger sequence of candidate genes or focused/whole exome sequencing