Transcript loss of function” polymorphisms of the p2rx7 gene and - dr

“LOSS OF FUNCTION” POLYMORPHISMS OF THE P2RX7 GENE AND PERIPROSTHETIC
OSTEOLYSIS AFTER TOTAL HIP ARTHROPLASTY: A PILOT STUDY.
Petřek M1, Mrázek F1 , Stahelová A1, Kriegová E1, Gallo J2
1 Laboratory
of Immunogenomics and Proteomics, Dept. of Immunology
2 Dept. of Orthopaedics
Palacky University and University Hospital Olomouc, Czech Republic
Background
Methods
Periprosthetic osteolysis
Periprosthetic osteolysis (OL) is dominant long-term
complication of the total hip arthroplasty (THA) which
can result in prosthetic failure and re-operation.
Pathogenesis of OL is complex – both biological and
mechanical factors play an important role.
Polyethylene wear particles liberated from the
prosthetic surfaces stimulate an inflammatory
response leading to osteolysis.
Substantial interindividual variability in the severity
of OL suggests implication of genetic factors.
P2XR7
Purinergic receptor P2X, ligand-gated ion channel, 7
(P2RX7) is activated by extracellular ATP.
P2RX7 is an important regulator of inflammation
and bone turnover, e.g. via effects on osteoclast
function and apoptosis.
Several variants of P2RX7 gene with critical effect on
P2XR7 expression / function have been described.
1. Subjects: 205 unrelated Czech patients with cementless type THA - stratified according to the
severity of OL (Table 1)
severe OL: N=116
mild/no OL: N=89
2. P2RX7 genotyping
- two selected loss-of-function polymorphisms (Table 2)
- Polymerase Chain Reaction with Sequence Specific Primers (PCR-SSP)
3. Statistics
- conformity of the distribution of genotypes to the Hardy-Weinberg equilibrium
- differences between allelic, genotype and phenotype („carriage rate“) frequencies:
Chi-square test
Mild OL
(Types I, II)
89
35/54
48 (27-58)
Patients, N
Gender (men/women)
Age at index surgery
Primary diagnosis:
Osteoarthritis
Dysplastic hip
Other diagnoses
Body weight (kg)
Body height (cm)
2
BMI (kg/m )
Linear wear rate
(mm/year.)
Severe OL
(Types III-V)
116
33/83
45 (24-68)
35
23
31
78 (54-118)
167 (153-195)
28.1 (20.3-35.7)
0.22 (0.04-0.92)
1) P2RX7 Glu496Ala (1513A/C, rs3751143)
Location: carboxyl terminus of the P2RX7
Functionality: abolished (ATP) induced ethidium up-take
2) P2RX7 Ile568Asn (1729T/A, rs1653624)
Location: trafficking motif within the P2RX7 carboxyl tail
Functionality: complete loss-of-function
13
62
41
73 (42-115)
164 (150-190)
27.2 (16.0-42.6)
0.34 (0.04-2.52)
PCR- SSP primers:
Severe (types III-V) and mild (I+II) osteolysis according to Saleh et al classification
J Bone Joint Surg Am, 83: 1040, 2001.
P 2R X 7 1 51 3 r ev A
5´ T
T
T
T
T
C
C
G
G
C
A G
C
A
C
A
G
C
T
P 2R X 7 1 51 3 r ev C
5´ T
T
T
T
T
C
C
G
G
C
A G
C
A
C
A
G
C
G
P 2R X 7 1 5 1 3 fw con st
5´ A
C
A
A
G
C
G
T
C
T
T
C
A
A
A
G
G
C
C
T
P 2R X 7 1 72 9 f w A
5´ G
A
C
A
T
G
G
C
T
G
A
C
T
T
T
G
C
C
A
A
P 2R X 7 1 72 9 f w T
5´ G
A
C
A
T
G
G
C
T
G
A
C
T
T
T
G
C
C
A
T
P 2R X 7 1 72 9 r ev con st
5´ G
T
A
C
A
G
A
C
A
G
G
A
T
T
T
C
G
C
C
T
Results
Hypothesis and Objective
The distribution of P2XR7 genotypes in THA patients corresponded to the H-W equilibrium and to the
frequencies observed in Czech and other Caucasian populations (Figure 1).
Wear Particles
By comparison with patients with no/mild osteolysis , the uncommon P2RX7 alleles (P2RX7 496Ala / 568Asn)
were overrepresented in the patients with severe osteolysis (p>0.05 Figure 2).
P2RX7 gene variants
Inflammation
Table 2: Investigated loss-of-function P2RX7 SNPs
variants and genotyping PCR-SSP primers
Table 1: Characteristics of subgroups of THA patients
stratified according to the secerity of osteolysis (OL)
P2RX7
Bone Turnover
Interestingly, rare P2RX7 568Asn allele was found only in patients with THA failure (carriage rate: 0.06) but
not in those with functional primary THA (0.00, p=0.09, Figure 3).
Figure 1: The frequencies of uncommon loss-of-function
P2RX7 alleles (P2XR7 496Ala, P2RX7 568Asn) in THA
patients and ethnically matched healthy subjects
Periprosthetic Osteolysis
Figure 2: Proportion of P2RX7 uncommon allele carriers
compared in patients with severe and mild/no OL
severe osteolysis
THA patients
Premature THA Failure
Healthy controls
0.25
0.2
0.189
allele carriage
Is there any association between the variants of
P2RX7 gene and susceptibility to periprosthetic OL/
premature failure after total hip arthroplasty?
allelic frequency
0.207
0.15
0.1
0.05
0.022
0.017
0
P2XR7 496Ala
mild/no osteolysis
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0.022
P2XR7 568Asn
Figure 3: Proportion of P2RX7 568Asn allele carriers compared
between THA patients with THA reoperation (failed THA) and
those with functional THA
P2RX7 568Asn allele carriers
The limitation of our pilot study is its suboptimal power to demonstrate an association of the
rare P2RX7 variant with OL and THA failure. Extension of our preliminary findings in larger
THA cohorts is, therefore, warranted. Studies of functionality of P2RX7 polymorphism in this
condition are desirable.
0.060
Allele carriage; severe versus mild/no osteolysis: p0.05
Allelic frequency; THA patients versus Controls: p0.05
Conclusions in patients with
In this pilot study, the rare P2RX7 568Asn allele tended to be overrepresented
THA failure by comparison with those with functional primary prosthesis.
0.337
P2XR7 496Ala
P2XR7 568Asn
Conclusion and Discussion
0.414
0.057
0.060
0.050
0.040
0.030
0.020
0.010
0.000
0.000
Failed THA
Functional THA
Allele carriage; Failed versus Functional THA: p=0.09
Supported by Czech Govt. Funding IGA MZ NR9490 and MSM 6198959205.