PHOP Core Fall 2016 Intro to Genetics and Ocular Development · 2017-09-08 · Gross Anatomy of the...
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PHOP Core Fall 2016 Intro to Genetics and Ocular Development
D. C. Otteson PhD UHCO 1
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Gross Anatomy of the Eye
Graw, Eye Development. (2010) inCurrent Topics in Developmental Biology (Volume 90) p. 343. 2
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From the National Eye Institute http://www.nei.nih.gov/photo/
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Body Axis Terminology
Caudal(posterior)
Ventral
Dorsal
Medial
Lateral
Rostral(anterior)
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Eye-specific Axis Terminology
Dorsal / Superior
Ventral / Inferior
Posterior Anterior
Nasal
Temporal
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http://www.becomehealthynow.com/article/bodyembryo/789/1
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GastrulationInduction and cell migration forms three germ layers
Ectoderm
Mesoderm
Endoderm
Gastrulation initiates at posterior end
Figure from Developmental Biology by Scott Gilbert. Sinauer Associates, Inc.
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(From Martin, Neuroanatomy Text and Atlas, Elsevier press)
Neural Crest
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Neural tube segmentation: brain vesicles
(From Martin, Neuroanatomy Text and Atlas, Elsevier press)
Mouse: day 8 post fertilization day 10-11 post fertilizationHuman: week 4 week 5
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Growth of cranial nerves
Dekaban, A.S. and Sadowsky, D, Ann. Neurology, 4:345-356, 1978
3-vesiclestage 5-vesicle stage
Telencephalongrows
Cortical maturation and expansion
NOT TO SCALE !!!!
EYE
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Graw (2010) in Seminars in Developmental Biology 90: 343.
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Primary Eye Field in Anterior Neural PlateEyes develop from cells in anterior neural plate
Eye field contains cells competent to form eye structures
Not all cells will actually contribute to eye structures
Early genes important in specification of eye fields:
Pax6, Rax/Rx, Six3, Tbx3, Six6, Otx2, Lhx2, TllSpecies: Mouse E7 ~Human E17
http://www.med.unc.edu/embryo_images/ 12
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Neurulation: Folding of Neural Plate
Neural plate grows rapidly
Eye fields in rostral neural plate expand
Eye fields separate at midline
Secreted sonic hedgehog (SHH) from notocord specifies ventral midline
http://www.med.unc.edu/embryo_images/
Species: Mouse E8 ~ Human E21View: Frontal
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PAX2 specifies ventral optic cup and optic stalkMutations: loss of ventral diencephalon, optic chiasm, ventral optic nerve coloboma, kidney and ear defectsHomozygous: lethal: no chiasm, no uritogenital tract
SHH secreted from notocord early embryoinduces ventral and midline structures in neural platerequired for separation of eye fieldsMutations: holoprosencephaly, cyclopia, midline facial defects, microcephaly
PAX6 specifies dorsal and lateral structuresneural retina, RPE, lens, cornea (+ non-ocular structures)Mutations: heterozygous: aniridia, glaucomahomozygous: (lethal) anophthalmia, failure to form nasal passage, brain defects
Separation of Eye FieldsSHH represses PAX6, induces PAX2
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Cells in Eye Fields Invaginate Forming Optic Grooves (a.k.a. optic sulci, optic pits)
Mouse E8.5 ~ Human E24 Fronto-Lateral
Mouse E8 ~ Human E22 View: Frontal
http://www.med.unc.edu/embryo_images/ 15
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Neural tube, rat development showing optic vesicles
Zhang, Fu, Barnstable (2002) Molec. Neurobiol. 26:137-152.
Rat embryo, E11.
Rostral view of neural tubeHead ectoderm removed
Arrows show anterior neuropore
ov=optic vesicles
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Species: Mouse E8.5 to 9 (~Human E25)
http://www.med.unc.edu/embryo_images/
Optic vesicle/Lens induction
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Mouse E 9 (~Human E28) Mouse E10 (~ Human E29)
http://www.med.unc.edu/embryo_images/
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Species: Mouse E11 (~Human E36)View: Coronal
Lens placode invaginates to form lens vesicle
Invagination of optic vesicle forms bilayered optic cup
Lens vesicle pinches off surface ectoderm
Overlying ectoderm becomes cornea
http://www.med.unc.edu/embryo_images/
Lens Vesicle and Optic Cup
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Species: Mouse E 11 (~Human E36)View: Coronal Cut
http://www.med.unc.edu/embryo_images/
Retina/RPEPax6 (+Mitf in RPE)
Lens vesiclePax6, Sox2/3
Optic StalkPax2
Irido-pupillary MembraneFrom neural crest
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Lens DevelopmentPrimaryFiber elongation
SecondaryFiber elongation
Graw (2010) in Seminars in Developmental Biology 90: 343.
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A model of a genetic switch composed of SOX2/SOX3 and Pax6, which regulates initiation of lens development.
Kamachi Y et al. Genes Dev. 2001;15:1272-1286
©2001 by Cold Spring Harbor Laboratory Press 22
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Lens maturationProliferation of cells at the equator Elongation of cells at bowFiber cells
nuclei are gone in central lenscells remain connected by gap junctions
Species: Human 8 Weeks http://www.med.unc.edu/embryo_images/ 23
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Lens Fiber Cells
Song et al J Clin Invest. 2009;119(7):1837–1848
Scanning electron micrographs of bovine lens fiber cells
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induced by lens• outer epithelial layer forms from surface ectoderm • inner layers primarily from neural crest cells
Image of cornea from: T. Caceci (2001) Anatomy and Physiology of the Eye V2.0
http://www.med.unc.edu/embryo_images/
Cornea
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RPE: Outer pigmented layer becomes relatively thinnerSingle cell layer RPE cells express PAX6 and MITF. Expression of MITF helps
specify RPE identity and this transcription factor directly regulates genes that are responsible for pigment formation in RPE.
RETINA: Inner, neural portion thickensPseudostratefied epitheliumDifferentiation begins at ~E11.5
Mouse Day E14 (~ Human 7 weeks) http://www.med.unc.edu/embryo_images/
RPE
Ventricle/Sub-retinalSpace
Retina
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The tunica vasculosa lentis From human fetus (a) Hyaloid artery (b) Posterior ciliary artery
From Duanes Ophthalmology 2006 Chapter 15: Lens, Kleiman and Worgul
Vasculature
Mouse(Gerhardt et al., 2003)
Superficial Plexus
Deep Plexus
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Iris and Ciliary Body Formation
Human ~15 Weekshttp://www.med.unc.edu/embryo_images/
Human 8 Weeks
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Ittner et al. Journal of Biology 2005 4:11
Neural Crest Derivatives in Eye
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Neural Crest
Ittner et al. Journal of Biology 2005 4:11 30
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Human: 8 Weeks
Eyelids
•begin to form at end of embryonic period
•fuse at the start of 2nd trimester
•reopen at the beginning of the 3rd trimester
Human: 10 Weeks
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Loci for Inherited Retinal Disease
RetNet; Stephen P Daiger PhDThe University of Texas Health Science Center, Houston, Texas
http://www.sph.uth.tmc.edu/RetNet
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genetics
DNA Replication and Inheritance
The basis of perpetuation of life and transmission of traits/genes
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Inherited vs. Non-inherited Mutations
• Germ-line mutations lead to inherited mutations– Occurs in germ line tissue– If mutation passes into gametes (egg, sperm), it will be passed
on to next generation. • e.g. sickle cell anaemia• Retinitis pigmentosa,• Keratoconus
• Somatic mutations occur in somatic tissues – Population of identical cells derived from a single mutated
somatic cell is a clone– Often results in a patch of phenotypically mutant cells– Not inherited – Many tumours result from somatic mutation– Two-hit theory of cancer e.g. retinoblastoma
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Heritable Genetic Changes
Single gene mutation Change in allele of a gene• Protein not expressed or• Protein non-functional or• Protein acquires novel/harmful/beneficial functions• Contributes to evolution
Chromosome mutation: multiple genes Changes in segments of chromosome Deletion, duplication, inversion, translocationLoss/duplication of whole chromosome
Epigenetic Changes
DNA modifications that can permanently change gene expression
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Genes + Environment= Phenotype
genes environmentphenotype
Contributions from genotype/environment varies with disease
Some diseases have both genetic and environmental components
e.g. macular degeneration; cataract; heart disease
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Classifying Mutations : Phenotypic Aspects
• Morphological mutations– Visible/measurable change in phenotype– e.g. eye color; ocular coloboma
• Lethal mutations– Heterozygous: normal– Homozygotes: do not survive– e.g. Cystic Fibrosis= mutation in CFTR gene–
• Conditional mutations – Phenotype only presents under specific conditions – e.g. predisposition for developing disease: diabetes, heart
disease, cancer: can change life-style and reduce risk
• Biochemical mutations– Change in enzyme, biochemical pathway components– e.g. Albinism (inability to synthesize melanin) mutations in
Tyrosinase and other enzymes of melanin biosynthesis
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Mutations: Mechanistic Aspects
• Silent mutations/Polymorphisms• Change in DNA sequence:
• doesn’t change sequence of protein (synonymous) – or • occurs in non-critical region of gene – Used for:– DNA “fingerprinting” – paternity analysis– genetic mapping (linkage analysis)
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Consequences of point mutations
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Gametes get one copy of each chromosome Gene R is on a separate chromosome from A and B and segregates independently of A and B
All allelic combinations are found: AB +R AB + r ab + R ab + rTherefore, R is not linked to the A or B genes
Genes A and B are on the same chromosomeParental allelic combinations inherited together (AB or ab)A and B genes are linked
Independent assortment of chromosomes during meiosis
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Predicting Patterns of Inheritance: Punnett Square
Genotype:B/B B/b b/b 1 : 2 : 1
Phenotype:Black brown
3 : 1
diploid
diploid
haploid
Shown: two alleles of a single gene
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Mendelian Non-MendelianAutosomal EpigeneticSex-linked MitochondrialRecessive ImprintingDominant MultifactorialMonogenic
Other including complexSyndromicSemi-dominant/co-dominant Sporadic/spontaneousDigenic
Patterns of Inheritance
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• Autosomal inheritance
– Based on the variation of single genes on regular chromosomes (autosomes)
• Sex-linked inheritance
– Based on the variation of single genes on sex-determining chromosomes
• Cytoplasmic inheritance
– Based on the variation of single genes on organelle’schromosomes (e.g. Mitochondrial)
Patterns of Inheritance
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Patterns of Inheritance: Recessive
Appearance of macula in Usher syndrome
Fundus pigmentation in Usher syndrome
Usher Syndrome I (human) USHIB mutations in MYO7A (Myosin7A)• Heterozygous (-/+) normal• Homozygous (-/-)
• profound congenital hearing impairment
• unintelligible speech• early retinitis pigmentosa (<10 yrs• vestibular dysfunction• defects in cilia (photoreceptor
connecting cilium; hair cells)
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Patterns of Inheritance: Recessive
•How to detect this pattern in patients?
•Can you distinguish this from spontaneous mutation?
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Parents: heterozygous
(+/-)
normal
+CSNB
-
normal
+CSNB
-Genotypes: +/+ +/- -/-Ratios (genotype)PhenotypesRatios (phenotypes)
Patterns of Inheritance: Recessive
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Parents: heterozygous
(+/-)
normal
+CSNB
-
normal
++/+ -/+
CSNB
-+/- -/-
Genotypes: +/+ +/- -/-Ratios (genotype)PhenotypesRatios (phenotypes)
1 2 1Normal Normal mutant
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Patterns of Inheritance: Recessive
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Parents:Heterozyous (+/-)
Homozygous (+/+)+ -
+
+Genotypes: +/+ +/- -/-Ratios (genotype)PhenotypesRatios (phenotypes)
Patterns of Inheritance: Recessive
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Parents:Heterozyous (+/-)
Homozygous (+/+)+ -
+ +/+ -/+
+ +/+ -/+Genotypes: +/+ +/- -/-Ratios (genotype)PhenotypesRatios (phenotypes)
1 1 0Normal Normal
1 0
Patterns of Inheritance: Recessive
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• Recessive genes are not major contributors in human genetic disease unless:
• highly consanguineous group• frequency of mutant allele in general population is
high• Difficult to determine if this is inherited or
spontaneous if only one affected individual
Patterns of Inheritance: Recessive
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Patterns of Inheritance: Dominant
• Dominant: Mutant allele is fully expressed and masks the expression of the allele.
• With true dominant, individuals heterozygous and homozygous for the mutated allele show the same phenotype.
• Haplo-insufficient: Absence of one allele results in intermediary phenotype; often referred to as semi-dominant
• Co-dominant: both alleles are fully expressed• e.g. blood groups (A, AB, B, O)
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genetics53
Patterns of Inheritance: DominantRetinitis Pigmentosa
Phenotype: • Constriction of the visual fields• Night blindness• Fundus changes• “bone spicule” lumps of pigment• Photoreceptor Degeneration• Variable age of onset
Multiple patterns of inheritance• Autosomal dominant• Autosomal recessive• X-linked
More than 3100 distinct mutations in 56 genes in have been identified(Daiger et al 2013 Clinical Genetics 84:132.)
From: www.stlukeseye.com/
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genetics54
Male unaffected
Male affected
Female
unaffected
Female affected
Patterns of Inheritance: DominantRetinitis Pigmentosa
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genetics55
Genotypes: +/+ +/- -/-Ratios (genotype)PhenotypesRatios (phenotypes)
ParentsHeterozyous (+/-)
Homozygous (+/+) + +
+-
Patterns of Inheritance: DominantRetinitis Pigmentosa
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genetics56
Genotypes: +/+ +/- -/-Ratios (genotype)PhenotypesRatios (phenotypes)
1 1 0Normal Mutant Mutant
1 1 0
ParentsHeterozyous (+/-)
Homozygous (+/+) + +
+ +/+ +/+- +/- +/-
Patterns of Inheritance: DominantRetinitis Pigmentosa
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genetics57
Patterns of Inheritance: Semi-Dominant HaploinsufficientAniridia
• Mutations in transcription factor Pax6• Haploinsufficient• Homozygous lethal• Heterozygotes: anterior segment
malformations:• aniridia• corneal clouding with variable
iridolenticulocorneal adhesions • Peters anomaly (central corneal leukoma,
absence of the posterior corneal stroma and Descemet membrane, and a variable degree of iris and lenticular attachments to the central aspect of the posterior cornea)
• foveal hypoplasia • glaucoma• autosomal dominant keratitis
A normal eye is pictured above. Below is the eye of a child with aniridia, a congenital eye disorder. People born with the disease have no iris and are generally legally blind.CREDIT ANIRIDIA FOUNDATION
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genetics58
Genotypes: +/+ +/- -/-Ratios (genotype)PhenotypesRatios (phenotypes)
ParentsHeterozyous (+/-)
+ -
+-
Patterns of Inheritance: Semi-Dominant / Haploinsufficient
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genetics59
Genotypes: +/+ +/- -/-Ratios (genotype)PhenotypesRatios (phenotypes)
1 2 1Normal Mutant More severe
1 2 1
ParentsHeterozyous (+/-)
+ -
+ +/+ +/-- +/- -/-
Patterns of Inheritance: Semi-Dominant Haploinsufficient
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genetics60
• Mutation on X chromosome
• Females: XX
• Males: XY
• Mutation/disease phenotype manifests in males
• Females are carriers, typically normal– But may manifest mosaic defects
• Generation skipping pattern
Patterns of Inheritance: X-linked
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genetics61
Examples of X-linked Retinal Diseases
OA1 X-linked ocular albinism
RP23,RP6, X-linked Retinitis Pimentosa
RS1 Retinoschisis
OPA2 X-linked optic atrophy
NDP Norrie disease; familial exudative vitreoretinopathy
Colorblindness (mutations in red/green opsin genes):
OPN1SW protan (red deficient)
OPN1LW deutan (green deficient)
blue cone monochromacy (red & green deficient)
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X-linked Diseases: X-inactivation
X chromosomes:Males have 1Females have 2
How to maintain same level of transcription (RNA levels) from X chromosome genes?
Random X-inactivation(Lyonization) in females
after Mary Lyon
e.g. coat color in cats 62
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X-inactivation of B-gal transgene in retina
http://mentor.lscf.ucsb.edu/course/winter/mcdb101b/x-inactivation/xinactivation.h
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X-inactivation in the cornea
John Westhttp://www.cip.ed.ac.uk/gallery/index.htm
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Mutant phenotype present in males x* Y Carrier females may show mosaic defects Xx*Skips generations
carrier
XY Xx*
XX x*Y XY Xx* XY x*Y XX
XY Xx* Xx* Xx* Xx* XY x*Y XX XX x*Y Xx* Xx* XY
Patterns of Inheritance: X-linked
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genetics66
Genotypes: X*X XX X*Y XYRatios (genotype)PhenotypesRatios (phenotypes)
Normal*carrier
Normal Affected Normal
ParentsFather affected X* Y
X
X
Patterns of Inheritance: X-linked
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genetics67
Genotypes: X*X XX X*Y XYRatios (genotype)PhenotypesRatios (phenotypes)
0 1 0 1
Normal*carrier
Normal Affected Normal
1 0 0 1
ParentsFather affected X* Y
X X*X XY
X X*X XY
Patterns of Inheritance: X-linked
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genetics68
Genotypes: X*X XX X*Y XYRatios (genotype)PhenotypesRatios (phenotypes)
Normal*carrier
Normal Affected Normal
ParentsMother-carrier X Y
X*
X
Patterns of Inheritance: X-linked
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genetics69
Genotypes: X*X XX X*Y XYRatios (genotype)PhenotypesRatios (phenotypes)
1 1 1 1
Normal*carrier
Normal Affected Normal
1 1 1 1
ParentsMother-carrier X Y
X* X*X X*Y
X XX XY
Patterns of Inheritance: X-linked
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Mitochondrial diseases affecting the eye
8-70
Ophthalmic manifestations of mitochondrial diseases:cataract, retinopathy, optic atrophy, cortical visual loss, ptosis and ophthalmoplegia
• Leber’s Hereditary Optic Neuropathy (LHON)
• Kearns-Sayre Syndrome (KSS)
• Mitochondrial Encephalopathy, Lactic Acidosis Stroke (MELAS)
• Myoclonic Epilepsy and Ragged Red Fiber myopathy (MERRF)
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genetics71
Patterns of Inheritance: MitochondrialLeber Optic Atrophy
• Presents in mid-life as acute or sub acute central vision loss leading to central scotoma and blindness
• Associated with many missense mutations in the mtDNA
• Mutations can act autonomously or in association with other mt mutations
• Final visual acuity can range from 20/50 to no light perception, depending on severity of the mutations
Leber Optic Neuropathy with temporal optic nerve pallor in both eyes.
http://www.revoptom.com/continuing_education/tabviewtest/lessonid/108143/
Healthy optic disc
http://www.intechopen.com/books/the-mystery-of-glaucoma/
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8-72
http://www.usc.edu/dept/mda/180evolution/IMAGES/wmho.html
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8-73
Patterns of Inheritance: Mitochondrial
Mitochondrial mutations: •inherited ONLY from the mother
•NEVER from the father
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ROM1/ROM1; ROM1/ROM1; +/ROM1 ; +/ROM1;RDS/RDS +/RDS RDS/RDS +/RDS
ROM1/ROM1; ROM1/ROM1; +/ROM1; +/ROM1;RDS/+ +/+ RDS+ +/+
+/ROM1; ROM1/+; +/+; +/+;RDS/RDS +/RDS RDS/RDS +/RDS
ROM1/+; ROM1/+; +/+; +/+;+/RDS +/+ RDS/+ +/+
Mode of inheritance: multigenicROM1/+; RDS/+ x ROM1/+; RDS/+
ROM1; RDS ROM1; + +; RDS +; +
ROM1; RDS
ROM1; +
+; RDS
+;+
Genotypes 1:2:1:2:4:2:1:2:1Phenotypes: 1:3:2:1:9