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Medical genetics in pediatrics
Kálmán Tory
Semmelweis University, Ist Department of Pediatrics
Key points
• The human genome
• Classification of the genetic disorders in the clinical practice
• How to identify the causal mutation in a monogenic disorder?
Key points
• The human genome
• Classification of the genetic disorders in the clinical practice
• How to identify the causal mutation in a monogenic disorder?
250M
2012 1203 1040 718 849 1002 866 659 785 745 1258 1003 318
200M 191M181M
171M159M
146M141M
48M 51M
601 562 805 1158 268 1399 533 278 522 905 96 13
155M
59M
0,017M
Number of bases per
chromosome:
Number of protein-
coding genes:
135M 135M 134M115M
107M102M
90M81M 78M
59M 63M
The 3.3 billion bases and the 20.000 genes of the nuclear genome
~3,5 Gb~23.000
~0,14 Gb~14.000
250M
2012 1203 1040 718 849 1002 866 659 785 745 1258 1003 318
200M 191M181M
171M159M
146M141M
48M 51M
601 562 805 1158 268 1399 533 278 522 905 96 13
155M
59M
0,017M
Number of bases per
chromosome:
Number of protein-
coding genes:
135M 135M 134M115M
107M102M
90M81M 78M
59M 63M
The 3.3 billion bases and the 20.000 genes of the nuclear genome
250M
2012 1203 1040 718 849 1002 866 659 785 745 1258 1003 318
200M 191M181M
171M159M
146M141M
48M 51M
601 562 805 1158 268 1399 533 278 522 905 96 13
155M
59M
0,017M
Number of bases per
chromosome:
Number of protein-
coding genes:
135M 135M 134M115M
107M102M
90M81M 78M
59M 63M
The mitochondrial genome is tiny as compared to the nuclear one
Which genome has a higher density of protein-coding genes?
1. the nuclear (100x).
2. the nuclear (10x).
3. the mitochondrial (10x).
4. the mitochondial (100x).
Which genome has a higher density of protein-coding genes?
1. the nuclear (100x).
2. the nuclear (10x).
3. the mitochondrial (10x).
4. the mitochondial (100x).
nuclear: 20 000 genes / 3 300 000 000 bases = 6 genes / Mb
mitochondrial: 13 genes / 17 000 bases = 760 genes / Mb
Key points
• The human genome
• Classification of the genetic disorders in the clinical practice
• How to identify the causal mutation in a monogenic disorder?
Types of genetic disorders
I. Nuclear genome (3G bases, 23 chromosomes, 20 thousand genes)
1. Chromosomal abnormalities
2. Monogenic disorders
3. Oligo- and polygenic diseases
II. Mitochondrial genome (17k bases, 37 genes)
Types of genetic disorders
I. Nuclear genome (3G bases, 23 chromosomes, 20 thousand genes)
1. Chromosomal abnormalities
2. Monogenic disorders
3. Oligo- and polygenic diseases
II. Mitochondrial genome (17k bases, 37 genes)
Different: patomechanism
methods of investigation
recurrence risk
Types of genetic disorders
I. Nuclear genome (3G bases, 23 chromosomes, 20 thousand genes)
1. Chromosomal abnormalities
2. Monogenic disorders
3. Oligo- and polygenic diseases
II. Mitochondrial genome (17k bases, 37 genes)
Chromosomal abnormalities= alterations of the copy number
Numerical Structural (Copy number variations)
Numerical chromosomal abnormalities
First genetic disorders with an identified origin (1958-1960)
1. Prevalence
– >50% of spontaneous miscarriages
– 0.6% in newborns
2. Method: karyogram
3. Pathomechanism
Miko, I. (2008) Mitosis, meiosis, and inheritance. Nature Education 1(1):206
http://cai.md.chula.ac.th/lesson/down_syndrome/contents/q08a.htm#Familial
3. Translocation with an elevated recurrence risk (≤10%)
The recurrence risk in numerical abnormalities
If the parents are not translocation carriers, the recurrence risk is:
2-4x higher than in the general population, but still <1-2%!
The typical pedigree in a chromosomal abnormality
= sporadic occurence
Numerical chromosomal abnormalitiesthat are compatible with extrauterine life
– Autosomal:
• Down (47,XX/XY, +21 )
• Edwards (47,XX/XY, +18)
• Patau (47,XX/XY, +13)
– Sex chromosomes
• Turner (45,X)
• Klinefelter (47,XXY)
• …
Down syndrome
• 47,XX/XY, +21
• often results in spontaneous miscarriage
• Incidence in newborns: 1:800
• life expectancy is ~50 years
• the region responsible for most of thephenotypic features is the 21q22 locus
Origin of trisomy 21
• meiotic non-dysjunction in 95%,
• translocation in 3%,
• mosaicism in 2% of cases
Typically has a maternal origin:
Rare autosomal trisomies
Patau syndrome
47,XX/XY, +13
cleft lip and palate
polydactyly
microphthalmia
Edwards syndrome
47,XX/XY, +18
overlapping fingers
microcephaly
prominent occiput
micrognathia
result from meiotic non-dysjunction in 90% of cases
leads to in utero death in 95% of cases
incidence at birth: ~1:5-10.000
life expectancy: few days – few weeks
cardiac abnormalities > 90%
severe developmental delay, renal disorder
Turner syndrome
• 45, X (mosaicism in 20%!)
• paternal origin in 80% (!)
• no relationship with maternal age
• causes in utero death in 98%
(15% of spontaneous miscarriages)
• incidence in newborns: 1:2.000
• short stature – haploinsufficiency of the SHOX gene
Turner syndrome
• 45, X (mosaicism in 20%!)
• paternal origin in 80% (!)
• no relationship with maternal age
• causes in utero death in 98%
(15% of spontaneous miscarriages)
• incidence in newborns: 1:2.000
• short stature – haploinsufficiency of the SHOX gene
Why X monosomy is pathogenic?
1. there are mutations on the single X chromosome
2. some genes cannot be transcribed from both chromosomes
3. the two X chromosomes cannot recombine
4. as the single X is inactivated in some cells, no X remains active
Why X monosomy is pathogenic?
1. there are mutations on the single X chromosome
2. some genes cannot be transcribed from both chromosomes
3. the two X chromosomes cannot recombine
4. as the single X is inactivated in some cells, no X remains active
Turner syndrome primarily results from the shortage of the
‘pseudoautosomal regions’ that are expressed from both sex chromosomes
Structural chromosome abnormalitiescopy number variations (CNV)
• CNVs: deletions, duplications (>1 kb)
• partly result from unequal recombinations during meiosis
1. copy number polymorphisms (CNP), small, typically <10kb
– 0.4% of the genome is different in CNPs between two individuals
(> single nucleotid polymorphisms!)
2. microdeletions and duplications (5MB - few 100kb)
– rare, a large CNV (>1 Mb) is found in only 1% of the population
– often pathogenic: enriched in patients with developmental delay, autism,
schizophrenia
• Rarely by karyogram (bad resolution)
(>4-10Mb!)
• Fluorescent in situ hybridization
(FISH, >200kb, better resolution, but targeted)
• Semiquantitave PCR-based methods
(high resolution, targeted)
• Comparative genomic hybridization
(CGH, >1kb), whole genome, high resolution
B (B )
QMP S F elektroferog ramja
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208 210 212 214 216 218 220 222 224
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negatív kontroll
vakvízA B
A Øheterozigótaság elvesztése
B (B )
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A Øheterozigótaság elvesztése
Q MP S F e le k tro fe ro g ra m ja
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vakvíz
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vakvíz
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vakvízA B
A Øheterozigótaság elvesztése
A B
A Øheterozigótaság elvesztése cycles fragment length
control
het del.
Detection of CNVs
typically dominant
recessive
Pathogenicity of a CNV
How to know whether a CNV is pathogenic or benign?
1. known CNP?
2. appeared de novo? (1/40 newborns carry a de novo CNV)
3. size? (>1 Mb is often pathogenic)
4. is there a known associated disease?
When to suggest a microdeletion syndrome?
Role of parental imprinting in the pathogenicity
Angelman syndrome
severe intellectual deficiency, inappropriate laughter, epilepsy
Prader-Willi syndrome
developmental delay, obesity, hypogonadism
deletion of 15q11-q13 (FISH)
Role of parental imprinting in the pathogenicity
Angelman syndrome
severe intellectual deficiency, inappropriate laughter, epilepsy
Prader-Willi syndrome
developmental delay, obesity, hypogonadism
deletion of 15q11-q13 (FISH)
Maternally inherited chr15 (UBE3A gene) Paternally inherited chr 15
Role of parental imprinting...
Liger (the largest big cat) Tigon
father: lion, mother: tiger father: tiger, mother: lion
Types of genetic disorders
I. Nuclear genome (3G bases, 23 chromosomes, 20 thousand genes)
1. Chromosomal abnormalities
2. Monogenic disorders
3. Oligo- and polygenic diseases
II. Mitochondrial genome (17k bases, 37 genes)
Typically result from single or
few nucleotide-alterations
1.5% of the genome is the coding region
normal sequence
A T G C G A T T A G A G T A C A T A A C G G G G
Met Arg Leu Glu Tyr Ile Thr Gly
silent polymorphism
A T G C G A T T G G A G T A C A T A A C G G G G
Met Arg Leu Glu Tyr Ile Thr Gly
non-silent polymorphism / missense variant
A T G C G A T T C G A G T A C A T A A C G G G G
Met Arg Phe Glu Tyr Ile Thr Gly
nonsense mutation (premature stop codon)
A T G C G A T T A G A G T A A
Met Arg Leu Glu STOP
Types of variants
normal sequence
A T G C G A T T A G A G T A C A T A A C G G G G
Met Arg Leu Glu Tyr Ile Thr Gly
in-frame deletion (involving 3 bases or its multiple)
A T G C G A T T A G A G T A C A T A A C G G G G
Met Arg Leu Glu Tyr Ile Thr Gly
A T G C G A T T A T A C A T A A C G G G G
Met Arg Leu Tyr Ile Thr Gly
Out of frame deletion (number of inserted nucleotides is not divisible by three)
A T G C G A T T A G A G T A C A T A A C G G G G
Met Arg Leu Glu Tyr Ile Thr Gly
A T G C G A T T A A G T A C A T A A C G G G G A
Met Arg Leu Ser Thr STOP
Types of variants
Typical differences in the coding sequencebetween an individual and the human reference genome
Mutation
• hundreds coding / individual
• appeared more recently in the human evolution
• might be pathogenic in monogenic disorders
SNP
• 20.000 coding / individual
• appeared >several 10k years ago in the human evolution
• undergone evolutionary selection
allele frequency = 1% <<
Mutations and polymorphisms
Methods
Sanger sequencing Next-generation sequencing largescale – even whole exome or genome
Diseases with an identified molecular basis
37 34 30 34 3660 60 51 47
84
56 49
8869 64
86
128122
93
130124146
195
160
335
246266
252242224
0
50
100
150
200
250
300
350
400
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
20
13
20
14
20
15
20
16
∑ > 5400 (2019.09.)
Human Genome Project
Exom-sequencing
Monogenic diseases
• result from defects in a single gene
• affect 1-2% of the general population
• responsible for 20% of infant mortality and 10% of pediatric inpatient care
• typically result from mutations (role of polymorphisms is exceptional)
• inherited in a Mendelian fashion:
– if one deleterious allele is enough to be pathogenic: dominant
– if both required: recessive transmission
recessive disease ≠ homozygous mutation
compound heterozygous
(the two mutations are different)
homozygous
(mutations of the two alleles are the same)
AR disorders may develop if the parents carry mutations in the same gene
Typical family pedigrees in autosomal recessive disorders
- the family history is often negative
- consanguinity (or inbred populations) are risk factors
compound heterozygous
(the two mutations are different)
homozygous
(mutations of the two alleles are the same)
AR disorders may develop if the parents carry mutations in the same gene
Typical family pedigrees in autosomal recessive disorders
Congenital nephrotic syndrome
• Two-weeks old newborn
• NPHS1:
– c.1048T>C , heterozygous p.S350P
– c.468C>G , heterozygous, p.Y156*
Autosomal recessive disorders
• >1700 disease / trait
• typical transmission in severe childhood disorders
• cystic fibrosis, enzymopathies / inborn errors of metabolism, storage
disorders, steroid-resistant nephrotic syndrome, nephronophthisis and the
vast majority of ciliopathies, congenital hepatic fibrosis…
Autosomal dominant transmission
• 4500 AD disease / trait
• How can a single deleterious allele be pathogenic?
– haploinsufficiency (~deletions of chromosomal regions)
– gain of function (Huntington, amyloidosis)
– dominant negative effect (osteogenesis imperfecta)
– second somatic mutation (ADPKD)
50% is not enough
somatic mutation of the
normal allele results in
clonal proliferation
the abnormal protein is
damaging for the cell
the abnormal
protein is damaging
for the polimer
Offspring of affected individuals have
a 50% risk of being affected
Autosomal dominant transmission
Is this pedigree compatible with an AD
inheritance?
De novo mutations
• All children inherit 50-100 de novo mutations (!)
• 1-2% of them are located in the coding regions
• thus, children in general carry ~1 de novo exonic mutation
• most of the de novo mutations have a paternal origin
– spermatogenesis necessitates 20-25 mitotic divisions per year
– oogenesis necessitates 20-30 mitotic divisons in total
• paternal age correlates with the number of de novo mutations
X-linked inheritance
• X-linked recessive • X-linked dominant
Males are more severely affected in both cases
Females and males are unequally affected
Duchenne, Alport,
haemophilia A, B
hypophosphatemic rickets
Types of genetic disorders
I. Nuclear genome (3G bases, 23 chromosomes, 20 thousand genes)
1. Chromosomal abnormalities
2. Monogenic disorders
3. Oligo- and polygenic diseases
II. Mitochondrial genome (17k bases, 37 genes)
Oligogenic inheritance
Bardet-Biedl syndrome
Katsanis et al.: Science,
2001;293:2256-9
Oligogenic inheritance
Mutation of a second gene explains the incomplete penetranceKatsanis et al.: Science,
2001;293:2256-9
Polygenic diseases
• often multifactorial disease, with genetic components, modified by the polymorphisms / mutations of several genes
• familiar clustering of these disorders is much less important than in monogenic diseases, often appear as sporadic cases
• congenital heart defect, non-syndromic cleft lip and palate, hypospadias, neural tubedefects
• neurodevelopmental deficiencies (autism, learning difficulties, schizophrenia) wereconsidered to polygenic – they have been found to result from de novo CNVs / pointmutations
Polygenic inheritance
recurrence risk in a first-degree
relative: 5-10%
UKNat Gen, 2009
n=2361
control = 4818
20q13
16q22
7q31
North-AmericaNat Gen, 2009
n=3426
control=11963
16p11
22q12
10q22
2q37
19q13
Polygenic diseases – ulcerative colitis, Crohn’s
Which loci are implicated in the pathogenesis?
JapanNat Gen, 2009
n=1384
control=3057
13q12
1q23
7q31
Types of genetic disorders
I. Nuclear genome (3G bases, 23 chromosomes, 20 thousand genes)
1. Chromosomal abnormalities
2. Monogenic disorders
3. Oligo- and polygenic diseases
II. Mitochondrial genome (17k bases, 37 genes)
Mitochondrial inheritance
There are ~1500 mitochondrial proteins. Most of them are encoded by the nuclear genome!
Mitochondrial DNA is inherited maternally.
Each cell contains thousands of copies of mitochondrial DNA. A mutation may affect only part of
the mitochondrial DNA (‘heteroplasmy’) or may affect all (‘homoplasmy’).
The difficulty of risk prediction: the mitochondrial genetic bottleneck
random shift of mtDNA mutational load between generationsTransfer of small number of mt DNA
Is it possible to be heterozygous for a mitochondrial mutation?
1. Yes, if one of the two mitochondrial DNA copies contains the
mutation.
2. No, all mitochondrial DNA copies are identical.
3. No. Though the sequence of the mitochondrial DNA copies can be
different, there are several copies, not only two, so it is not possible to
be heterozygous for a mitochondrial mutation.
4. Yes, if approximately half of the DNA copies contain the mutation.
Key points
• The human genome
• Classification of the genetic disorders in the clinical practice
• How to identify the causal mutation in a monogenic disorder?
Why is it important to know which gene
is responsible for a disorder?
• Identification of the mutation confirms the clinical diagnosis
• helps to determine the recurrence risk for the affected families
• allows studying the pathomechanism
• might already influence the therapy
• Autosomal recessive disorders • Numerical chromosome abnormalities
• De novo single nucleotide mutation • Deleterious copy number variations
In severe diseases, the family history is often negative
What is important in the family history?
• Potential consanguinity? Where are the parents from? Do theyoriginate from the same small population? (suggestive of homozygousmutations in recessive disorders)
• Maternal age? (numerical chromosome abnormalities)
• Paternal age? (de novo point mutations)
Phenotype
informative not informative
phenotype suggestive
of CNVs
malformation
CGH array
phenotype suggestive of
a monogenic disorder
exome sequencing
Filter: Ø
No characteristic phenotype, but a monogenic origin is
suggested, let us sequence the exome…
Filter: polymorphisms excluded (frequent variants are unexpected to cause rare diseases)
No characteristic phenotype, but a monogenic origin is
suggested, let us sequence the exome…
Filter: polymorphisms and previously found variants excluded
No characteristic phenotype, but a monogenic origin is
suggested, let us sequence the exome…
Turnpenny, Ellard: Emery's
Elements of Medical Genetics
Filter: polymorphisms, previously found variants, intronic, intergenic and silent variants excluded
No characteristic phenotype, but a monogenic origin is
suggested, let us sequence the exome…
• Allele frequency
• Evolutionary conservation
• Amino acid change
Rodriguez G et al. Circ Cardiovasc Genet. 2011;4:349-358
How to select the potentially pathogenic missense variants?
• Allele frequency
• Evolutionary conservation
• Amino acid change
How to select the potentially pathogenic missense variants?
Filter: keeping only mutations that are predicted to be pathogenic
No characteristic phenotype, but a monogenic origin is
suggested, let us sequence the exome…
Filter: as the parents are consanguineous, only HOMOZYGOUS mutations predicted to be pathogenic are kept
No characteristic phenotype, but a monogenic origin is
suggested, let us sequence the exome…
The causal mutations in a monogenic disorder are typically:
• rare in the general population (allele frequency < 0.1%)
• lead to truncation of the protein or affect evolutionary conserved amino acids
• segregate with the disease in the family wtǀQ2158Xwtǀwt
wtǀwtwtǀQ2158X
wtǀQ2158X
Despite all precautions, not every mutations,
published as causal, are pathogenic...
New Engl J Med, 2010Slide from Stanislas Lyonnet
SH3TC2
New Engl J Med, 2010
174 HGMD
159 „surely pathogenic”
21 monogenic disease
- 16 heterozygous
- 4 homozygous
- 1 hemizygous
ABCD1
Once we identified the causal mutation, it is easy to test unaffected family members, but it may raise ethical problems
Even parents are not allowed to ask for presymptomatic testing of
their offspring if no treatment is available for the disease
Identification of the
causal gene
animal
model
subcellular localization of the
encoded protein
protein-interactions
signaling pathways
organ-specific
expression
genotype-phenotype correlations
Identification of causal genes is a milestone in the understanding of the pathomechanism
Gallagher et al: Molecular Advances
in ADPKD, Chronic Kidney Disease,
Volume 17: 118-30
Cystic kidney disorders are secondary to mutations of genes encoding primary cilium proteins
The mitotic angles of renal tubular cells are altered in rats with polycystic kidney
Fischer et al.: Defective planar cell polarity in polycystic kidney disease. Nat Genet. 2006
normal lengthening of a
renal tubule is due to
mitotic divisions
the altered mitotic divisions
lead to cyst formation
Simons M, Walz G: Polycystic kidney disease: Cell division without a c(l)ue?
Kidney International 2006
The mitotic angles of renal tubular cells are altered in polycystic kidney disease
Summary
• The human genome currently does not really explain the differences
between humans and animals.
• The methods of investigation have undergone a revolutionary
development during the last two decades.
• If we cannot establish a clinical diagnosis, it can be still very difficult
to identify the genetic cause in monogenic diseases.
Recurrence risk in polygenic disorders
• Difficult to determine
• If several family members are affected, it may be mono- or oligogenic
• A rough estimation:
The risk in first-degree relatives is the square root of the prevalence in the general population
Szteroid-rezisztens nephrosis szindróma
Újszülöttkori diabetes mellitus(kezdet: <6 hó, 1:100.000-500.000)
Permanens
(50%)
Tranziens
(50%)
KCNJ11 (Kir6.2)
35-50%
ABCC8 (SUR1)
~7%
Brinkman et al. Nature Reviews Genetics 2006
ABCC8 (SUR1)
~15%
aktiváló, gain-of-function mutációk
Akut lymphoid leukemia
Jó prognózis
• t(1,19) (5%)
• t(12,21) (20-25%)
• hyperdiploid
Rossz prognózis
• t(9,22) (Ph+) (3-4%)
• t(4,11) (5%)
• hypodiploid
A leggyakoribb gyermekkori malignitás.
Ross et al. Blood 2003;102:2951-9
Nagyon magas rizikó
5 éves túlélés: 46%
Alacsony rizikó
5 éves túlélés: ~90%
Neuroblastoma
A 3. leggyakoribb gyermekkori malignitás.
Az N-myc gén 50-400x amplifikációja a
neuroblastomák 25-30%-ában található meg.
Rossz prognózissal társul:
Stage I vagy II neuroblastomában a teljes túlélés az
N-myc gén-amplfikáció függvényében: 72 vs. 90%
(n = 2660)
Mikor nem szabad genetikai vizsgálatot végezni?
1. Tünetmentes kiskorú genetikai vizsgálata nem engedélyezett (a szülők
kérésére sem), ha a gyermeknek nem származik előnye a diagnózis
ismeretéből.
2. Ki szeretné ismerni milyen mutációkat hordoz?
Az egy- és kétgyermekes szülők többsége nem tudja, hogy születhetett volna beteg gyermekük!
9/16 potenciálisan beteg gyermeket nemző kétgyermekes szülőpár nem tudja,
hogy a gyermeke beteg lehetett volna
Terápiás lehetőségek
Liu X L et al. JASN
2004;15:1731-1738
2004 by American
Society of Nephrology
wild type
nephrin
nephrin
actin HEK293
cells
Mutáció-specifikus kezelés az NPHS1 mutációt hordozó betegben
500mg Na 4-phenylbutyrate/day
Patomechanism
Összefoglalás - módszertan
Összefoglalás
• A vizsgáló módszerek fejlődésének köszönhetően egyre több betegség genetikai hátterét ismerjük meg.
• Ez döntő a betegségek patomechanizmusának megismerésében, oki terápia kifejlesztésében.
• A közeljövőben már nem a genetikai eltérés azonosítása lesz kihívás, hanem annak eldöntése, hogy mi patogén és mi nem.
• A genetikai vizsgálatok indikációját alaposan meg kell fontolni. Nem kell mindent tudjunk.
Van ~23.000 génünk, sok ezer betegség
Honnan lehet tudni, hogy egy betegségért melyik gén felelős?
Honnan lehet tudni, hogy egy betegségért melyik gén felelős?
Egy családban két beteg és két egészséges gyermek van.
A betegek tünetei megfelelnek az ARPKD tüneteinek, tudjuk
tehát, hogy recesszíven öröklődik.
De tegyük fel, hogy a génje nem.
Honnan lehet tudni, hogy egy betegségért melyik gén felelős?
Honnan lehet tudni, hogy egy betegségért melyik gén felelős?
Honnan lehet tudni, hogy egy betegségért melyik gén felelős?
Statisztikailag a genom ¼-e felel meg ennek az eloszlásnak.
Honnan lehet tudni, hogy egy betegségért melyik gén felelős?
Honnan lehet tudni, hogy egy betegségért melyik gén felelős?
Ennek a megoszlásnak – statisztikailag - a genom ¼ * ¾ * ¾ = 9/64-ed része felel meg.
3.000 Mb x 9/64 = 420 Mb (még mindig óriási terület)
Az ARPKD locusa: 6p21
Zerres K et al.: Mapping of the
gene for autosomal recessive
polycystic kidney disease
(ARPKD) to chromosome
6p21-cen.
Nat Genet. 1994 7:429-32
De: a lehetséges gének száma ~100
A PKHD1 identifikálásaWard CJ et al.: The gene mutated in autosomal recessive polycystic kidney disease encodes a large, receptor-like protein. Nat Genet. 2002, 30:259-69.
A PKHD1 által kódolt fehérje, a polyductin
Sok más cisztás
vesebetegségben mutáns
proteinhez, a polyductin is
csillófehérje
Szerkezete egy
receptoréra emlékeztet
Az MKS3 allélok és a fenotípus közötti kapcsolat
1. allél
2. allél0
1
vad típus
hypomorph
funkcióvesztett
MKS3 allél
De egy gén nem csak egy betegséget okozhat!
Ugyanazt a betegséget több gén mutációja is okozhatja (genetikai heterogenitás),és egy gén több betegséget is okozhat – monogénes betegségekben is!
PKD1
wtǀQ2158Xwtǀwt
wtǀQ2158XwtǀQ2158X
wtǀQ2158X
25 yrs: neg. US
Rossetti S et al., Kidney Int, 2009 Vujic M et al., JASN, 2010
PKD1
wtǀR220WR3277Cǀwt
R3277CǀR220W
Dg: In utero
Újszülött: Resp. insuff.
8 yrs: cisztás vese
R3277CǀR220W
Dg: In utero
Újszülött: Resp. insuff.
1 yr: cisztás vese
41 yrs: neg. US 34 yrs: neg. US
Ugyanazon gén különbözői mutációi eltérően öröklődhetnek... ADPKD recesszív öröklésmenettel?!
Domináns öröklésmenet Recesszív öröklésmenet
wtǀwt
Miért különbözünk egymástól?
Jelentős részben a Single Nucleotid Polimorfizmusoknak (SNP)
köszönhetően:
>18 millió SNP ismert (a
(a 3,3 milliárd bázisból)
minden 150-200. bázis egy SNP
1. ember
2. ember
3. ember
A cisztás vesebetegségeket csillófehérjéket kódoló gének mutációi okozzák
All offspring of a 21q21q translocation carrier are affected by Down syndrome
http://cai.md.chula.ac.th/lesson/down_syndrome/contents/q08a.htm#Familial
3. Translocation
Human Genom Project
• nuclear genome sequence in 9 individuals (8 men)
• human genome consists of 3,3 milliárd bázisból áll
• ~3 billion $
Frytillaria assyriaca
Miért nem szekvenálunk exomot mindenkinél?
• Ez a jövő...
• De: több ezer variánst, több tucat mutációt találunk mindenkinél
• Melyik a patogén?
• Lehet egyszerű a választás (a fenotípus ismeretében), de előfordulhat, hogy heteket kell tölteni az analízisével
A rendelkezésre álló módszerek
Domináns vagy recesszív betegség az ADPKD?
Miért lesz neonatalis az ADPKD? Negatív anamnézisű családban
neonatalis ADPKD?
PKD1
wtǀQ2158*wtǀwt
wtǀQ2158*wtǀQ2158*R3277Cǀwt
R3277C ǀ Q2158*
ESRD: 43 yrs
Dg.: 15 yrs
CRF: 44 yrs
25 yrs: neg. US
Dg.: in
utero
CRF: 17 yrs
Rossetti S et al., Kidney Int, 2009 Vujic M et al., JASN, 2010
PKD1
Dg: In utero
Neonate: Resp. insuff.
8 yrs: cystic kidney
Dg: In utero
Neonate: Resp. insuff.
1 yr: cystic kidney
41 yrs: neg. US 34 yrs: neg. US
Offspring of affected individuals have
a 50% risk of being affected
Is this pedigree compatible with an AD
inheritance?
Autosomal dominant transmission
AR transmission – risk calculation
~100%
probability of being carrier
probability of being affected50%
⅔ 2pq
⅔ x 2pq x 0,25 = 0,7% for the nephew to be affected
cystic fibrosis: prevalence: q2=1/2500, q=1/50=2%, p=98%,
frequency of carriers in the general population: 2pq ~ 4%