Unit 2 - 11. Molecular Methods in the Diagnosis of Genetic Diseases Flashcards Preview

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Flashcards in Unit 2 - 11. Molecular Methods in the Diagnosis of Genetic Diseases Deck (16):

6 uses of genetic tests

1. Diagnostic testing
2. Predictive testing
3. Carrier testing
4. Prenatal testing
5. Preimplanatiation testing
6. Newborn screening


1. Diagnostic testing

- noninvasive way to confirm or rule out a diagnosis of a genetic disorder in a symptomatic individual (may not always be the best method of diagnosis)


2. Predictive testing

- offered to asymptomatic individuals with family history to predict whether eventual development of symptoms is certain or likely if present genetic mutation
- controversial - treatment may not be available


3. Carrier testing

- offered to individual with family history or have a higher risk (ethnic/race) to identify carriers of a gene in recessive disorder
- allows reproductive choices


4. Prenatal testing

- offered when there is increased risk of having a child with genetic disorder
- performed on fetal samples obtained by amniocentesis, chronic villus sampling (piece of placenta), and etc.


5. Preimplantation testing

- offered to couples with high chance of having a child with serious genetic disease
- performed on early embryos from in vitro fertilization
-only unaffected embryos are selected for implantation


6. Newborn Screening

- legally mandated (varies by state)
- performed routinely at birth to identify newborns with genetic disorders to begin treatment as early as possible
- ex: PKU


Direct Testing

- testing for specific gene mutation that is directly related to the disease
- used on monogenic disorders and requires that the mutated gene has been identified
- preferred over indirect testing


Indirect Testing

- tracing the inheritance of a mutated gene in a family along with known genetic markers which are located within (intragenic) or close to (extragenic) a target gene = Linkage analysis
- performed when direct testing is not possible because disease gene has not been identified or due to a number of mutations


Cyctic Fibrosis

= autosomal recessive

Mutation: at CFTR gene on long arm of chromosome 7 which codes for a protein that regulates chloride ions across plasma membrane
- most common mutation = delta F508 - deletion of 3-base codon for phenylalanine at 508

Detection: Direct testing using PCR and gel electrophoresis
- Diagnostic, carrier, and prenatal testing via fluorescence-based testing


Duchenne Muscular Dystrophy

= X-linked recessive

Mutation: mutation in gene that codes for the muscle protein, dystrophin
- can be a number of mutations but most are deletions

Detection: PCR amplifications


Huntington Disease

= autosomal dominant

Mutation: multiple CAG repeats in gene coding for Huntington protein

Detection: PCR


Fragile X Syndrome

= X-linked dominant

Mutation: multiple CGG repeats at FMR1 gene (>200)

Detection: Southern Blot



- restriction fragment length polymorphism
- DNA finger printing/profiling
- one type of marker
- genetic variations in length of DNA fragments resulting from restriction endonucleases
- mutations here may effect a restriction endonuclease site


Linkage Analysis

- used to determine whether a family member is likely to carry a disease gene based on pattern of markers inherited


Limitations to Linkage Analysis

1. Family members must be willing to participate
2. Family must be informative (carriers are heterozygous for mutant allele)
3. Recombination of extragenic markers can affect accuracy (the further the marker, the less accurate)