Genetic disorders Flashcards
What is an epigenetic trait?
A stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence (in vitro fertilisation)
Basis of epigenetics
Cells have identical DNA but diff terminal phenotypes
Non-genetic cellular memory - records developmental and environmental cues (stimulus may only occur once but is remembered for lifetime)
What could epigenetics explain?
Not always possible to identify genetic determinants which fully explain heritability of complex traits
Inability to pinpoint causative genetic effects in complex diseases
3 characteristics of epigenetics
Heritable
Self-perpetuating
Reversible
What can epigenetics affect?
DNA methylation
Histone modification
Nucleosome location
Non-coding RNA (miRNA)
Methylation epigenetics
Twin studies shown methylation can be affected by environment
Low levels of nutrients or toxins can affect enzymes that methylate DNA
Some genetic variants make people more susceptible to environmental factors that alter DNA methylation
Genes vs epigenetics
Genes are blueprint for creating proteins while epigenetics determines how genes are read
As well as passing on genes we pass on molecular switching & info about how genes should be expressed
Amy Cuddy expt
2 gps for 2 mins, either high power or low power position
- 86% HP opted to gamble, only 60% of LP
- testosterone: HP 8% increase, LP 10% decrease
- Stress hormone cortisol: HP 25% decrease, LP 15% increase
Most common trans epigenetic signal
Transcription factor
-activates its own transcription factor so epigenetic state is self-sustaining
Small RNAs can be trans signal
Epigenetic cis signals
Cis signals are physiclaly associated with DNA e.g. DNA methylation or changes in histones
DNA methylation and disease
- Methylation used to silence genes by blocking binding of other proteins thus interfering with transcription (e.g. transcription factors)
- Abnoraml methylation demonstrated in Fragile X syndrome, may play role in some autoimmune disorders e.g. lupus or neurophychiatric disorders e.g. autism
- Cancer cells have abnormally low levels of methylation i.e. genes activated inappropriately or if excessive methylation some genes may be switched off (control cell division)
Zebularine in Human Liver Cancer
An integrated genomic and pharmacoepigenomic approach predicts therapeutic response of Zebularine in human liver cancer
- Zebularine = DNA methylation inhibitor
- Pxs are responders or non-responders
Genes and tooth development
Teeth develop in highly controlled & coordinated way
-interaction between cells of different embryonic origins
Teeth develop diff shapes depending on exact position in mouth and combination of genes expressed in area
Genetic pathways control tooth initiation and patterning
Growth factors control expression of genes early in tooth development but at later stages this control may be reversed
-examples: diff animals diff teeth and ‘small white pearls’ (odontoma)
PAX9
Mutation of PAX9 associated with oligodontia
-oligodontia: rare genetic disorder in which more than 6 teeth are absent
GREMLIN2
GREM2 is strong BMP antagonist - regulates BMPs in embryogenesis and tissue development
- isolated tooth agenesis, microdontia, short tooth roots, taurodontism, sparse & slow growing hair, dry & itchy skin
- other tooth related genes not involved
MicroRNAs in tooth development
Discrete miRNA expressed in molars compared with incisors
Diff in those expressed in epithelium compared with mesenchyme
Why do mammals only have one row of teeth? What controls this?
Antagonistic actions of Msx1 and Osr2 pattern
This also plays a role in cleft palate development
Cleft susceptibility genes
BMP2 and BMP 4
MSX1
Number of genes found close together on chromosome 6
-if not expressed at right time there will be problem with development
AXIN2
Mutations in AXIN2 cause familial tooth agenesis and predispose to colorectoral cancer
Genes and disease
Riegers syndrome Wolf-Hirschhorn Williams Kabuki Ectodermal dysplasia Holopreosencephaly
Riegers syndrome
Hypodontia with malformation of anterior camber of eye, one form caused by mutations in homeobox transcription factor PITX2
Wolf-Hirschhorn syndrome
Short arm of chromosome 4, transcription factor MSX1
Williams syndrome
Mutation in elastin gene
Ectodermal dysplasia
150 clinically distinct hereditary syndromes, defects in morphogenesis of ectodermal structures e.g. teeth, nails, hair, skin
Holoprosencephaly
Abnormalities in forebrain cleavage and midface development
What is the most common chronic disease worldwide?
Dental caries
GWAS
Examine genome-wide set of genetic variants in diff individuals to see if any variant is associated with a trait
Genes and dental caries
Taste genes associated with dental caries
Amelogenesis Imperfecta
Group of developmental conditions which affect structure and clinical appearance of enamel
Can be isolated or as part of syndrome
AMELX
Alteration of conserved alternative splicing in AMELX causes enamel defects
-exon 4 is almost always spliced out but here a silent mutation in exon 4 means it is included in the mRNA transcript for amelogenin
Gene therapy saliva example
Salivary glands target sites for gene therapeutics
Overexpression of transgene product = ‘overflow’ exits via constitutive into bloodstream
Advanages of salivary glands
- well-encapsulated, limiting undesirable spread of vector
- luminal membranes of epithelial cells easy to access relatively non-invasively
- ductal access uses limited fluid volume not diluted following delivery (low vector doses)
- well differentiated & slowly dividing
- make > protein for export
- single SG not crucial for life and can be removed
Protein secretion pathways from salivary glands
Predominant leading to saliva (musocal; across apical membrane)
Constitutive leading mainly towards interstitium and bloodstream (serosal; across basolateral membrane)
Overexpression of transgene product = ‘overflow’ exits via constitutive into bloodstream
How many cases of oral cancer per year in USA
35-40,000
5 year survival rate oral cancer USA
53% 1975-1977 to 60% 1996-2004
Treatment for oral cancer
Radiation therapy, side-effects overcome by
- hyberbaric oxygen
- chemoprevention
- surgical gland transfer
- intensity-modulated RT
hAQP1
Human aquaporin-1 encodes water channel that facilitates rapid transmembrane water movement in response to osmotic gradient
hAQP1 to restore salivary flow
In absence of acinar cells due to RT NaCl is not reabsorbed in isotonic primary salivary fluid
Duct cells could generate osmotic gradient (lumen > insterstitium) that water could follow
Transfer of the hAQP-1 cDNA into surviving duct epithelial cells would provide this pathway
–> increased fluid secretion from irradiated gland
Treating renal anaemia in swine model
Delivery of human erythropoietin gene to parotid glands through Stensen’s duct
> hEPO conc in parotid saliva and serum
Kidney damage not completely reversed but gene transduction of hEPO via parotid is promising potetial alternative therapy for renal anaemia
Stem cells and teeth
Adult human gingival epithelial cell as source for whole-tooth bioengineering
- epithelial cells injected into mesenchyme tissue, cultured for 5 days, transplanted into kidney capsules of adult mice
- 6 weeks later kidneys removed and examined for ‘human’ tissue
What are exosomes
Durable, cell-specific lipid microvesicles
Can migrate through vasculature
Reside in biofluids e.g. urine, blood, breast milk, bronchial lavage fluid, CSF, saliva
True functions unknown, suggested could range from immune response regulators to tumour invasion promoters
Exosomes as salivary biomarkers
Tumour-derived exosomes could function as shuttle between distal tumour and oral cavity - discriminatory salivary biomarkers
