genotype-phenotype correlation in pku szeged, december 12, 2011
TRANSCRIPT
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
N-terminal regulatory domain: AA 1–142Catalytic domain: AA 143–410C-terminal domain: AA 411–452→ tetramerization
PAH enzyme
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
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
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
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
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
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
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%
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
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
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
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
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