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Genotype-phenotype correlation In PKU Szeged, December 12, 2011.

Genotype-phenotype correlation In PKU

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Szeged, December 12, 2011. Genotype-phenotype correlation In PKU. Introduction. HPA – BH4-responsive – classic atypical (BH4-dependent) Severity depends partially on the mutation of PAH enzyme - PowerPoint PPT Presentation

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Page 1: Genotype-phenotype correlation  In PKU

Genotype-phenotype correlation In PKU

Szeged, December 12, 2011.

Page 2: Genotype-phenotype correlation  In PKU

Introduction

HPA – BH4-responsive – classic atypical (BH4-dependent)

Severity depends partially on the mutation of PAH enzyme

Genotype correlates with the metabolic phenotype in most of the cases – homozygous, severe null mutations

… or „mild” mutations

Most of the patients are compound heterozygous (or – in Hungary - R408W homozygous)

There are significant genotype-phenotype inconsistencies between identical PAH mutation bearing patients

So the PKU/HPA phenotype manifestation is more complex than it could be predictable based on the Mendelian inheritance of the mutated alleles

Page 3: Genotype-phenotype correlation  In PKU

N-terminal regulatory domain: AA 1–142Catalytic domain: AA 143–410C-terminal domain: AA 411–452→ tetramerization

PAH enzyme

Page 4: Genotype-phenotype correlation  In PKU

www.pahdb.mcgill.ca

12q22-q24.1, 13 exon

564 mutation

PAH gene mutations

0,5%

0,7%

3,2%

5,0%

5,7%

11%

13,5%

60,5%

Un

kno

wn

No

nse

nse

Sp

lice

Mis

sen

se

0 50 100 150 200 250 300 350 400

Page 5: Genotype-phenotype correlation  In PKU

PAH gene mutations

Metabolic phenotype BH4-responsiveness Mutation type

mild Mostly responsive (80%) mild/mild

moderate May be responsive, depending of the „mild” mutation type

mild/null

severe (classic) Non-responsive null/null

Page 6: Genotype-phenotype correlation  In PKU

BH4-responsive PAH mutations

~70 known mutation

Mostly point-mutation (never splice, insertion or deletion)

Mostly in the catalytic domain, but not in the cofactor-binding site

Page 7: Genotype-phenotype correlation  In PKU

BH4-responsive PAH mutations

Page 8: Genotype-phenotype correlation  In PKU

mutáció allél

R408W 45 null

A403V 5 may be responsive

IVS12+1G>A 5 splice, null

R261Q 5 may be responsive

L48S 4 responsive

IVS10-11G>A 3 splice, null

IVS3-22C>T 3 silent

R158Q 3

IVS7-4delT 3 unknown, splice?

c.15delCT 2

P281L 2 null

IVS11+1G>A 2 splice, null

c.39delC 2

IVS4+5G>T 2 splice

mutáció allél

E390G 1 responive

T380M 1 responive

Y414C 1 may be responsive

R252W 1 null

IVS4+47C>T 1

P225T 1

IVS10+94G>A 1 silent

IVS7+1G>A 1 splice

I174V 1

V177L 1

IVS4-5C>G 1 splice

S350Y 1

Q172X 1 null

G148D 1 unknown

M276T 1

I95F 1

R243X 1 null

V245A 1 HPA

F302V 1 unknown

Page 9: Genotype-phenotype correlation  In PKU

Our cases: null mutations

Since 2006 we could not have the patients' DNA sequenced

52 patients' DNA sequence and mutations are known

Classic PKU: null mutations

Allél 1 Allél 2 esetszám mutáció típus

R408W R408W 14 missense

IVS12+1G>A IVS11+1G>A 2 splice

R408W IVS10-11G>A 1 missense/splice

R408W IVS12+1G>A 1 missense/splice

Page 10: Genotype-phenotype correlation  In PKU

Mutation BH4-response (allele %)

In vitro residual enzyme activity (%)

L48S 83 39 Regulatory domain

A403V 100 32 Catalytic domain

E390G 100 72 Catalytic domain, enzyme surface

Y414C 93 36 Tetramerization

R261Q 86 38 Active site secondary structure, tetramerization

R158Q 56 10 Catalytic domain

Trefz et al. J Inherit Metab Dis (2009) 32:22–26

Non-null mutations

Page 11: Genotype-phenotype correlation  In PKU

BH4 loading with 20 mg/kg bw in 3 patients, all genotype Y414C/R408W.

Lindner M et al, Mol Genet Metab 2001; 73:104-106.

Y414C (mild)/R408W (null) → moderate PKU?Same genotype – different BH4-responsiveness

Y414C BH4-resp: 93% Residual enzyme activity: 36%

Page 12: Genotype-phenotype correlation  In PKU

HPA cases

Allele 1 Allele 2 Phe level (mol/l) BH4 loading test?

T380M wt 130 not performed

E390G A403V 180 not performedno diet

S350Y A403V 240 not performedon diet

Page 13: Genotype-phenotype correlation  In PKU

Interesting cases

Allele 1 Allele 2 Phe level Remark

KA R408W R261Q 600-1200 on diet

Matalon 2005 BH4-responsive

Desviat 2004 non-responzive

Erlandsen 2004 partially responsive

DG R252W ? 300-1200

Page 14: Genotype-phenotype correlation  In PKU

Tesztelt BH4-reszponzív esetek

Allél 1 Allél 2 Phe szint Megjegyzés

SZB & SZF IVS7-4delT A403V 360 BH4-reszponzív

NÁ R408W A403V 240 BH4-reszponzív

UIA V245A R158Q 240 BH4-reszponzív

Page 15: Genotype-phenotype correlation  In PKU

Pathogenic mutation phenotype 1

phenotype 2

Genetically determined factors:other intragenic differences, polymorphismsmodifying genes: aminoacid transport, competition, metabolism, excretion

Non-genetically determined factors

phenotype 3

Genotype-phenotype in PKU

Page 16: Genotype-phenotype correlation  In PKU

Confirming the genotype may help in the judgement and predicition of the severity of the disease

There are significant genotype-phenotype inconsistencies between similar PAH mutation bearing patients: mainly the regulatory domain mutations lead to unpredictable phenotype, in the cases of compound heterozygosy

BH4-loading test result may vary in a patient - intracellular environment, metabolic status influence the mutated enzyme activity

The standard(ized) Phe+BH4 loading test is the gold standard for planning the treatment!

Conclusion