Unit 2 Day 8 Flashcards
genetic testing definition
- analyzing an individual’s genetic material to determine predisposition to particular conditions or to confirm diagnosis
- risk or diagnosis*
- examine blood/fluid/tissue for markers (biochemical, chromosomal, genetic) that indicate presence/absence of disease
loose definition of genetic testing
tests informing risks/diagnosis of genetic disease
- genetic tests are not solely restricted to DNA basis*
- other tests can diagnose genetic conditions*
what is chromosomal analysis useful for?
- identifying aneuploidies (trisomy 21)
- identifying large chromosomal structural changes (duplication, deletion, rearrangements)
- 3-5 mb
WAGR syndrome
- high resolution chromosmal analysis
- wilims tumor, aniridia, genitourinary malformation, retardation
- on 11p13, must be 3-5 mb or larger
- find w/ PAX6 locus in FISH
Fish analysis
- specific, cost efficient if know/strongly suspect the diagnosis
- micro-dup/del syndromes
what test do you use when you don’t know the diagnosis?
a “genomic” test
CMA-chromosomal microarray analysis
- test and reference DNA sample targets
- labeled w/ diff colors and washed across array covered in probes
- abnormal ratios indicate deletions/duplications
microarray/aCGH
- array comparative genomic hybridization
- looks for deletions, shows them in same location
- can compare sizes of similar deletions to see which zone is the critical disease region
dna sequencing
- mutations in known genes, polymorphic variants, small (1-100nt) deletion/insertions
- looks at sequence of known disease gene
- DETECTS NOVEL MUTATIONS
- may miss larger deletions
diagnostic testing
- patient with signs/symptoms of disease
- positive genetic test result confirms diagnosis
predictive testing
- patient with no signs/symptoms of genetic disease
- positive genetic provides estimate of future disease risk
allelic heterogeneity
different mutations (alleles) at a single locus
genetic heterogeneity
different mutations (alleles) at different loci
- SC: 1 mutation, 1 gene
- CF: many mutations, 1 gene
- AD: many genes/mutations
informativity as a concept when genetic test is normal
- some negative results are truly negative
- other negative results are non-informative (do not exclude diagnosis/risk)
OTC Deficiency
- X linked disease
- Urea cycle defect
- designed for healthy OTC patients, Jessie Gelsinger enrolled for therapy
- adenoviral vector + otc gene used
- he died after large dose of intra-hepatic drugs (treatment may have tempered if they had looked at bloodwork)
chromosomal mutation challenges
- cannot remove, silence, regulate extra chromosomal material
- cannot insert missing material
single gene mutation challenges
- cannot remove, silence, or regulate single genes
- cannot insert single genes
complex (genes+environment) mutation challenges
- cannot remove, silence, or regulate multiple genes
- cannot insert multiple genes
- gene environment interactions not fully understood
genetic approach to human diseases
- general management
- primary disease specific therapies (if they exist)
- genetic counseling
- secondary prevention
- primary prevention
therapies for metabolic disorders
- usually due to enzyme deficiency
- some can do dietary/pharmacological intervention
- newborn screening, early diagnosis, treatment (less morbidity)
treatment strategies for metabolic disorders
- avoidance
- dietary restriction (PKU)
- replacement
- diversion
- inhibition
- depletion
protein replacement approaches
- Alpha-1 AT: autosomal recessive, deficient, elastases unchecked, treat w/ recombinant AT1 therapy
- Fabry: x linked, deficient in alpha-galactosidase a, treat with recombinant Alpha-gal
Fabry treatments
- glucose injections
- chaperone based therapies
- enzyme replacement therapy
- chaperone + enzyme
challenges to protein-based therapies?
production, delivery, targeting, imm. reactions, cost
gene therapy
- intro of dan into human cells to treat disease
- should cure/slow progression of disease
- done with non-viral (naked DNA and liposomes), adenoviral (dna viruses), and retroviral (rna viruses)
- includes in vivo and ex vivo strategies
x linked disorders
- mutations on x chromosomes
- mostly affects males
- no male to male transmission
x linked recessive inheritance
- phenotype expressed in all males who carry affected genotype
- phenotype in homozygous females only
- heterozygote females=carriers
x linked dominant inheritance
-expressed male hemizygotes and female heterozygotes
x linked dominant diseases
Hypophosphatemic Rickets Alports Fragile X Syndrome Charcot Marie Tooth Incontinentia Pigmenti Rett Syndrome Orofaciodigital Syndrome Focal Dermal Hypoplasia
hypophosphatemic rickets
- 1/20000
- short stature
- bone deformity
- mutation in PHEX regulates fibroblast growth factor
- kidneys unable to reabsorb phosphate
fragile X
-x linked, CGG repeats
-1/2500-4000 males; 1/7-8000 females
-most common cause inherited mental delay
-maternal transmission bias
-dysmorphic features, autistic, biting, aggression, etc.
-FMR1, FMRP, Xq27.3 mutation
-protein for normal cognitive development/female reproductive function
46-55 repeats is grey zone
56-200 is premutation
>200 full mutation
rett syndrome
- x linked dominant
- 1/10000 females
- 95% new mutation rate
- abnormal movement/coordination, loss communication, failure to thrive, seizures
- MECP2 mutation
- Methyl Cpg bp, impt nerve cells
x linked recessive disorders
Lesch-Nyhan Syndrome Dystrophinopathies Hunter’s Disease Menkes Disease Glucose 6 phosphate dehydrogenase deficiency Hemophilia A and B Wiscott Aldrich Syndrome Colorblindness
lesch-nyhan syndrome
- x linked recessive
- 1/ 380000
- neurological/behavioral abnormalities
- uric acid overproduction
- HPRT1 mutation (recycles purines)
dystrophinopathies
- x linked recessive
- spectrum muscle disease
- Duchenne and Becker Muscular Dystrophy
- DMD mutation, dystrophin
- Xp21-21.1 (largest human gene)
duchenne musc. dystrophy
- progressive muscular weakness
- calf weakness
- ck levels=10x
- dead in 30’s, absence dystrophin
Becker muscular dystrophy
- progressive muscular weakness
- ck levels=5x
- later onset, dead 40’s
- abnormal quantity/quality dystrophin
hemophilia A
- recessive
- 1/4000
- 10% female carriers affected
- F8 mutation
- Xq28
- 50% caused by 22A inversion
replicative segregation
- at cell division, multiple copies of tDNA replicate and sort randomly among newly synthesized mitochondria
- normal or mutated DNA
Kearns-sayre
- mitochondrial inheritance
- 1-3/100000
- somatic mutation
- affects eyes, cardiac conduction, ataxia, deafness, kidney issues
- deletion of mtDNA (removes 12 genes commonly)
MELAS
-Mitochondrial encephalomyopathy
-1 in 300,000
-Low new mutation rate
-muscle weakness, seizures, stroke-like episodes, lactic acidosis
80% caused by mutation in MT-TL1
MERRF
-mitochondrial
-Myoclonic epilepsy with ragged-red fibers
-1/400000
-low new mutation rate
-muscle symptoms, seizures, ataxia, dementia
mutations in MT-TK
leber hereditary optic neuropathy
- mitochondrial inheritance
- 1/30-50000 europeans
- vision loss
- mutations in MT-ND genes
achondroplasia
- major features: prenatal, rhizomelic short stature, spinal cord compression, brainstem compression
- 1/40000
- beteen 3-7% die unexpectedly in 1st year
- due to advanced paternal age
- autosomal dominant
- FGFR3 Gly380Arg substitution–>gain of function
- spinal cord compression (and apnea) most feared complication
nonsyndromic deafness
- congenital deafness is commonly recessive form
- progressive childhood deafness is the dominant form often
- 3/4 of genetic are non syndromic. GJB2 mutations are most common mutation.
syndromic deafness
- systems outside of ears involved
- different combinations can indicate different diseases/syndromes
GJB2 mutations
- recessive inheritance for severe congenital
- parents=carriers
- LOF mutations
- autosomal dominant progressive with childhood onset
- genetic, autosomal recessive, non syndromic deafness due to this mutation=most common category of congenital deafness*
FMR1 Gene
- fragile X syndrome
- haplotype effect, full triplet expansion
- premutation vs. mutation
- full mutations have absent/reduced FMRP protein
- premuations are not hypermethylated, have increased FMRP RNA
- fragile X triplet repeat is in 5’UTR region
