Transcript Mutations changes of genetic information

The Pathogenesis of Diseases from
Genetic and Genomic Point of View
Part 3 - Nonmendelian
Rácz and František Ništiar
Institute of Pathological Physiology
Medical School, Šafárik University
2015/2016
©Oliver
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NONMENDELIAN FORMS OF
INHERITANCE
Expansion of trinucleotide repetitions
(dynamic mutations)
 Imprinting
 Mitochondrial genes and genetics
 Errors in alternative splicing
 (This chapter is NOT about the inheritance
of complex diseases)
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Expansion of trinucleotide
repetitions (dynamic mutations)
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Increased number of triplets (not insertions) 
disease ???
Increase of repetition number from one generation
to the next (anticipation)
Does not fit into our concept of classical genetics,
molecular biology and mutations
More repetitions, more severe disease
Only in humans ???
Mostly in noncoding regions
Also in exons, but only CAG = Glu
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DIFFERENT POSSIBILITIES
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Expansion of trinucleotid
repetitions (dynamic mutations)
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sy. Martin & Bell, mental retardation, X - linked
(fragile X, FRAXA) men 1/1000; women 1/2500
– FRAXE, mental retardation (X) less severe
– Myotonic dystrophy (m. Steinert, AD)
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Huntington disease (AD) ataxia & dementia
– Spinal & bulbar muscular atrophy (AR),
spinocerebellar atrophy type 1, Haw River sy, Machado
- Joseph disease (all AD)
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Friedreich ataxia (AR)
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29  29  29  29  29  29  29  29
55  75  95  120  200  325  500
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sy. Martin & Bell,
mental retardation, X - linked
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The second most common cause of mild mental
retardation (IQ 60 – 20)
Specific signs – elongated face, big ears,
macrorchidism, mitral valve prolapsus
1/1550 m; 1/2500 f
A fragile region of the long arm of X (incubation
in special medium – without folic acid)
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sy. Martin & Bell
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Xq27, gene FMR-1,
chromosome breaks, hypermethylation
CGC repetitions in noncoding 5’ region
6 - 53 (mostly 29)
norm, stable
54 - 200
„premutation“ expansion
200 - 4000
full mutation,
methylation affects the promotor region (OFF)
Asymptomatic men pass the defect to their
daughters, increase of triplet number,
manifestation in the next generation
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sy. Martin & Bell
The coded protein is FMRP
 Functions of FMRP
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– High expression in brain and testes
– Binds to ribosomes and the complex is
transported through axons and dendrites near to
synapses
– Regulates the translation of specific proteins of
nervous system
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Decreased expression – mental retardation
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Zero generation
Man, premutation, healthy
First generation
All daughters carriers of permutation,
healthy
Sons healthy
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A daughter of first generation
Change to full mutation during
oogenesis
Why? How? Always?
SECOND AND FURTHER
GENERARIONS
Sons affected with 50% probability
They are fertile!!!
Daughters 50% mild signs
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Group of neurodegenerative
diseases - Huntington (+ 7 others)
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Only nervous tissue, death of a specific group of cells;
manifestation in early adulthood
In Hungtinton repetitions in exons - > 35 CAG = > 35
Glu in protein
Gain of function mutations
Lot of unanswered questions
– why in adulthood ?
– why a specific group of cells ?
the expression of a (mutated) gene depends on a
lot of other genes !!!gene15c
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Huntington
1872 George Huntigton in age
22 years „on chorea“
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Huntington
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Progressive ataxia (chorea) and decrease of cognitive and
mental functions. Broad scale of symptoms, big individual
differences
Beginning typically in age 35 – 44 years, sometimes earlier –
poor prognosis
Heredity is formally dominant
The faulty protein is prone to aggregation
The diagnosis of mutated gene is possible – and thereafter???
– Positive = fate, negative = „survivor guilt“
Therapy only symptomatic
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Epidemiology
5 – 10/100 000 (SK 300 – 400)
 Are they diagnosed ? (not only HD)
 Exceptions
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Lake Maracaibo, Venezuela 700/100,000 but
also Tasmania and some regions in EU
An example of „founder effect“ (big families)
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Friedreich ataxia
Rare AR disease (1/50 000)
 Multisystemic - beside symptoms of
nervous system cardiomyopathy and
disorders of glucose metabolism
 gene - frataxin
 repetitions GAA in the 1st intron
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– norm 7 - 22, disease 200 - 900 (splicing ???)
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Also classic mutations lead to disease
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Imprinting - absolutely against Mendel
Mendel: Homologous autosomes (mother =
father) are equivalent (globin a chains)
 Imprinting - different expression of genes on
homologous chromosomes (mother father)
 Oddity? Prader - Willi & Angelman sy.
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PWS: Muscle hypotony, mental retardation, bulimia eat everything what they find, also from garbage
AS: Mental & motor retardation, agressivity, do not
sleep („happy puppet syndrome“)
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PWS & AS are different diseases
Caused by deletions of the 15th ch.
 PWS - deletion on CH15 from father
 AS - deletion on CH15 from mother
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P
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P
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M
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And this is only the beginning!
Uniparental disomy
P
P
M
PWS !
AS !
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M
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Different expression of genes on paternal
and maternal chromosomes
A
B
C
D
E
P
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A
B
C
D
E
M
The same genes are present
on both chromosomes
For normal function we need
expression of one set ABCDE
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Different expression of genes on paternal
and maternal chromosomes
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A
B
C
D
E
A
B
C
D
E
P
M
For normal function we need
expression of one set ABCDE
This can be achieved by imprinting
(block) of some genes on paternal
and maternal chromosome
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Explanation
for normal development gene cooperation is
necessary
 some genes expressed only on maternal,
others on paternal chromosome
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Deletions of maternal on paternal chromosome
ABCDE
OK
AC
BDE missing
BDE
AC missing
Uniparental disomy
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Explanation
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for normal development gene cooperation is
necessary
some genes expressed only on maternal, others on
paternal chromosome
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AC m + BDE p = ABCDE (O.K.)
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Deletion „m“
Deletion „p“
two „p“
two „m“
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expression BDE not enough
expression AC not enough
expression BBDDEE not enough
expression AACC not enough
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Mechanism
methylation of regulatory regions of genes
 catch 22 - what is occuring in the next
generation ?
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AC
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AC
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We should something to do with it
&
&
OVUM AC & BDE
SPERMIUM AC & BDE
PROBLEM WITH THEIR COMBINATION
50 % children with PWS or AS
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We should something to do with it
&
&
OVUM AC & BDE
SPERMIUM AC & BDE
Removal of the old sign
introduction of new imprinting according to the sex
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We should something to do with it
&
&
OVUM
SPERMIUM
Removal of the old sign
introduction of new imprinting according to the sex
MOTHER
FATHER
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Parthenogenesis is not working
 The
development of zygotes 46 XX or
46 XY is normal only when the
chromosomes are from both parents
 Experiments on mice
 46 XX from mother - teratoma
 46 XY from father - mola hydatydosa
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Is it really so rare ?
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About mice and men
Growth, obesity, energetic metabolism
gene for IGF2 is active paternal CH7 in mouse
gene for IFG2 receptor is active on maternal CH17
Pathogenesis of Type 2 diabetes ???
The cooperation of paternal and maternal part of
genome is not so peaceful ???
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Mitochondrial genetics
In the cells there is one nucleus with two
sets of chromosomes (= Mendel’s laws)
 In the cells there is a great number of
mitochondria in each of them more copies of
circular two-chain DNA (16569 bp) HETEROPLASMIA
 Maternal genetics (Eve from Bible?)
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Functions and pathology of
mitochondria
Citrate cycle
 Steroid synthesis
 Terminal oxidation
 Damaged in hypoxia, repefusion damage
(release of free radicals)
 Mitochondria and aging
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The structure of mtDNA
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16959 bp
Heavy & Light chain and
D-loop (triple)
Both chains code genes
(without intrones)
13 proteins
2 rRNAs (!)
22 tRNAs
Small noncoding regions
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Characteristics of mtDNA
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Without histones
800 – 1000 copies (up to
10 000) in a cell
Maternal heredity
Higher mutations rate as
in nDNA (ROS, weak
reparation mechanisms
and also tissue specificity
Replicative segregation
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UGA = stop (Trp)
AUA = Ile (Met)
AGA/AGG = Arg (stop)
Ribosomes similar as in E.coli
(chloramfenicol sensitivity)
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Genes of terminal oxidation
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COMPLEX
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SUBUNBITS IN nDNA
and mtDNA
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I. NADH dehydrogenase
II. Succinate
dehydrogenase
III. Ubichinone:
cytochrome Coxidoreductase
IV. Cytochromoxidase
V. ATP synthase
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I.
35 – 7
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II.
4–0
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III.
IV.
V.
9–1
13 – 3
12 – 2
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Mitochondrial diseases
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Mutations of mtDNA - nonmendelian
– Sporadic („somatic“), deletions, duplications,
affecting protein coding genes or tRNAs
– Maternal („gametic“), point mutations or
microdeletions
– The combination of both (!)
Mutations in genes of nDNA coding
mitochondrial proteins – mendelian
 Defects of intergenomic signaling
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Mitochondrial diseases (mtDNA)
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Not very common with long names
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KSS – Kearns-Sayre sy
LHON – Leber hereditary optic neuropathy
MERFF – Myoclonic epilepsy, ragged red fibers
MELAS – Myopathy, encephalopathy, lactic acidosis, apoplexia
Mutations in the genes for tRNAs (?!)
Forget it – remember only that most of the symptomes
are consequences of altered energy production in tissues
with high energy demand – muscles, heart, brain, senses
Do not forget it – 22 y. old man with symptoms of
stroke, CT negative ??? MELAS !
Accumulation of mutations – explanation of aging?
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